Ebook Histology for pathologists (4/E): Part 2

Part 1 book “Histology for pathologists” has contents: Serous membranes, small intestine, vermi orm appendix, anal canal, gallbladder and extrahepatic biliary system, the lymph nodes, bone marrow, urinary bladder, ureter and renal pelvis, penis and distal urethra,… and other contents.

Serous Membranes Darryl Carter ■ La w re n ce Tru e ■ Ch ris to ph er N Otis

2 1

REACTIVE MESOTHELIUM 595 Reactive versus Neoplastic Mesothelium 596 Reactive Mesothelium versus Carcinoma 596 Endosalpingiosis and Endometriosis 597

Fibrous Pleurisy 598 Multilocular Peritoneal Inclusion Cyst 598 REFERENCES 599

ANATOMY 585 FUNCTIONAL ANATOMY 586 MESOTHELIAL CELLS 588 Morphology 588

Histochemistry 589 Immunohistochemistry 591 Ultrastructure 593

SUBMESOTHELIAL LAYER 593 Histochemistry 593

Immunohistochemistry 595 Interactions o Mesothelial and Submesothelial Cells 595

ANATOMY

The mesothelium lines the pleural, pericardial, and toneal cavities Mesothelial cells on the serous surfaces appear as a simple or cuboidal epithelium, although they are of mesodermal origin They are supported by a brous submesothelial layer, which becomes continuous with the outer layer of invested viscera The serous membranes show functional differentiation according to their derivation from visceral or parietal mesoderm

peri-Because of space limitations, description of the gross anatomy of the mesothelium must be somewhat trun-cated, but some areas have functional differentiation that

is re ected by their histologic features The pleura is a continuous membrane that covers the chest wall and the lungs The visceral pleura coats the entire pulmonary sur-face, including the major and minor ssures that divide the lungs into lobes, whereas the parietal pleura extends over the ribs, sternum, and supporting structures and is re ected over the mediastinal structures on both right and left Pos-teriorly in the mediastinum, the two layers of parietal pleura are separated by a thin band of brovascular connective tis-sue Superiorly, the cervical pleura is re ected into the ret-roclavicular area over the apex of the lung and is coated by a

thickened layer of brous tissue and skeletal muscle; orly, the diaphragmatic pleura represents its caudal extent

inferi-Anteriorly, the pleura is re ected over part of the dium The posterior visceral pleura becomes continuous with the diaphragmatic pleura over the pulmonary ligament

pericar-The heart and great vessels lie in the pericardium, which is lined by a continuous layer of mesothelium The visceral (epicardial) side is connected to the myocardium, and the parietal (pericardial) layer rests on a dense brous tissue layer containing branches of the internal mammary and musculophrenic vessels, descending aorta, and branches of the vagus, phrenic, and sympathetic nerves The thoracic surface of the pericardium is coated with parietal pleura

The peritoneum is a nearly continuous membrane ing the potential space between the intra-abdominal viscera and the abdominal wall In females, it is normally inter-rupted by the lumina of the fallopian tubes Anatomically, it

lin-is more complex than either the pleura or the pericardium

The parietal layer covers the abdominal wall, diaphragm, anterior surfaces of the retroperitoneal viscera, and the pelvis The visceral peritoneum invests the intestines and other intra-abdominal viscera The elongated structures in which the parietal and visceral layers come together are the mesentery, which contains blood vessels, lymphatics, lymph nodes, and nerves

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The greater omentum is a double sheet with four layers

of mesothelium between which there are numerous blood vessels and adipose tissue, which may be abundant; lym-phatics and lymph nodes are less prominent than in the mesentery The peritoneal cavity is grossly divided into the greater sac over the intestines, the retrogastric lesser sac, the right and left retrocolic areas, and the pelvis Several outpouchings of peritoneum are often seen in pathology laboratories Inguinal hernia sacs are pouches of parietal peritoneum, often invested with brous tissue and occa-sionally with skeletal muscle, which have been pushed through the abdominal musculature into the inguinal canal

Umbilical or ventral hernias are also outpouchings of toneum, but the specimens received by pathologists after surgery for their repair are usually preperitoneal broadi-pose tissue pushed ahead of the parietal peritoneum rather than mesothelium itself

peri-The scrotum acquires a lining of parietal mesothelium, the processus vaginalis, into which the testes descend during the seventh month of gestation A mesothelial layer forms the sur-face of the tunica vaginalis Distention of this mesothelial sac

on the tunica vaginalis results in a hydrocele— communicating with the peritoneal cavity when congenital but noncommu-nicating in acquired hydroceles The sac of an inguinal her-nia communicates with the peritoneal cavity and not with the mesothelium-lined space of the scrotum Both hernia and hydrocele sacs are capable of a wide range of reactive changes

FUNCTIONAL ANATOMY

The functional anatomy of the pleura was described by Sahn (1) and Pistolesi et al (2) The pleura is a continu-ous membrane surrounding a space that normally contains approximately 10 mL of clear colorless uid The surface

is lined by a single layer of mesothelial cells anchored to

a basement membrane that lies on layers of collagen and elastic tissues containing vascular and lymphatic vessels

The lining mesothelial cells are 16 to 40 µm in diameter, have rounded nuclei, usually displaying a nucleolus, and a relatively large amount of cytoplasm Although the visceral and parietal pleurae are opposing parts of the same con-tinuous membrane, there are major functional differences between them

The human visceral pleura is thick relative to that seen

in some other mammals (3) and is similar to that of horses, cattle, sheep, and pigs (4) It has an arterial blood supply from the bronchial arteries, with a venous return that passes rst into the pulmonary veins and then into the left atrium except for certain hilar regions that are drained by bron-chial veins into the right atrium The lymphatics that pass through the visceral pleura are the super cial layer of pul-monary lymphatics with extensive connections to the peri-bronchial, perivascular, and interlobular lymphatic spaces

and lymphoid tissue (5) Blood and lymphatic vessels are invested by two layers of collagen and elastic bers; an external elastic lamina supports the mesothelial cells and

an internal layer invests the vessels and becomes ous with the pulmonary interstitium (Figures 21.1, 21.2)

continu-Histologic identi cation of integrity of the visceral ral elastin is considered clinically important in determining pleural invasion by primary lung cancer, which is signi cant for staging (6) However, the elastin layer of the visceral pleura is also interrupted in non-neoplastic conditions of the lung that extend to the pleura In sheep, and probably

pleu-in humans, the thickness of the external layer pleu-increases

in both the craniocaudal and ventrodorsal directions, haps because of postural reasons (7) The visceral pleura is innervated by branches of the vagus nerves and sympathetic nerve trunks

per-The parietal pleura is anatomically, histologically, and functionally different Although the single layer of meso-thelial cells that lie on the surface of the parietal pleura are cytologically similar to those that form the continuous membrane over the visceral pleura, they are interrupted by stomata which range in size from 2 to 12 µm in diameter

Li (8) described the stomata on the human diaphragmatic pleura as usually penetrating deep through connective tis-sue with apparent communication between the pleural cav-ity and the underlying lymphatic lacunae In some areas, stomata were covered with great microvilli (longer and

FIGURE 21.1 Visceral pleura The mesothelial cells on the sur ace are

f attened and, when viewed in pro le, so thin as to be barely evident On the posterior sur ace o the le t lower lobe, the dense submesothelial layer is composed o collagen and elastin, and extends into adjacent pulmonary interstitium and around pulmonary vessels.

CHAP TER 2 1 : Se ro u s Mem bran es 587

with a denser network of laments) on the surfaces of the surrounding mesothelial cells The underlying lymphatics drain directly into intercostal lymphatics and then into the mediastinum, where they are particularly dense along the ret-rocardiac surface (9–16)

Fluid and particulate matter extravasated from the lung are collected in these lymphatics and passed into the mediastinum, where the mesothelium covers collections

of macrophages called Kampmeier foci (17) Boutin et al

(18) showed concentration of asbestos bers in these areas, which are also termed “black spots” when there is concen-tration of carbon in individuals who have inhaled coal dust

Miserocchi et al (19) discussed asbestos ber tion in “black spots” corresponding to the stomata

accumula-The arterial and venous blood supply to the parietal pleura is from the intercostal vessels The thickness of the broelastic layer investing the parietal pleural lymphatics is relatively constant and considerably less than that of most

of the visceral pleura, suggesting that it serves as a brane across which uid may diffuse The parietal pleura is innervated by branches of the intercostal nerves, which are responsible for the pain associated with pleurisy

mem-Wassilev et al (20) described stomata on the neum of the abdominal wall, omentum, mesentery, ovaries and pelvis as well as on the underside of the diaphragm

perito-They found variation in the structure of the stomata ing to location The parietal stomata were clustered, oval in shape and delimited by attened mesothelial cells, whereas the hepatic stomata were deeper gaps in adjacent cuboidal

accord-mesothelial cells and were covered or occluded by the microvilli on the surface of mesothelial cells Li and Yu (21) found that the diaphragmatic stomata were approximately

10 µm2 in size, among cuboidal but not attened lial cells, and opened into submesothelial connective tissue

mesothe-in which there was a rich plexus of lymphatics, which they suggested carried away peritoneal uid and particles

The serous membranes serve as a selective barrier for uid and cells A small volume of uid is required for capil-lary action to facilitate adherence of visceral and parietal pleurae as the lungs and chest wall expand and contract

Elements of the serous membranes regulate uid change to keep this uid at a minimal level to prevent com-promise of the lung volumes Control appears to be at the capillary level because uid is freely diffusible through vis-ceral mesothelium and is collected in parietal lymphatics via stomata in the parietal mesothelium The bushy, elongated microvilli, which are the diagnostic hallmark of mesothelial cells, are sometimes enlarged where associated with sto-mata Another level of control results from the relatively low protein content (1.0 to 1.5 g/dL) of pleural uid The point

inter-of protein regulation is unknown, although there is tion that it occurs at the level of mesothelial microvilli (21)

specula-In the thoracic cavity, the direction of ow appears to be via diffusion from capillaries of both visceral and parietal pleurae, with resorption primarily through parietal pleural capillaries Turnover is estimated at 0.7 mL/hr (21) (Figure 21.3) Small molecules (less than 4 nm in diameter) dif-fuse through the intercellular spaces and junctions between mesothelial cells Loss of control results in serous effusions such as those seen in congestive heart failure

FIGURE 21.2 Visceral pleura Capillaries are prominent, the ics are dilated, deeply placed and entirely invested by the submesothe- lial layer.

lymphat-FIGURE 21.3 Model o the dynamics o pleural f uid ormation A sudate rom capillaries in visceral and parietal pleurae is partly reab- sorbed by those capillaries and the rest di uses into the pleural space, where it is resorbed via stomata into parietal pleural lymphatics.

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Larger molecules, up to 50 nm in diameter, are ferred across the mesothelium by pinocytotic uptake and transcellular transport Larger structures, such as cells

trans-in bloody effusions, are transported via the stomata and

“crevices.” Loss of control of these mechanisms results in accumulation of exudative pleural uid Mesothelial cells express the secretory component of IgA, which is other-wise limited to surfaces with direct environmental con-tact (22,23) The glycoprotein-rich pleural uid acts as a lubricant to minimize friction between visceral and parietal pleurae The site of synthesis and mechanisms of control

of the carbohydrate-rich fractions of the pleural uid are unknown The submesothelial connective tissue distributes mechanical forces from the pleura uniformly throughout the lungs Such a redistribution of forces is not required of the abdominal serosa Both mesothelial cells and broblasts contribute to collagen synthesis

MESOTHELIAL CELLS

Morphology

Normal mesothelial cells are rarely seen in histologic tions but may be evident in cytologic preparations of peri-toneal washes taken during a laparotomy (Figure 21.4)

sec-When thus visualized, they have abundant clear cytoplasm with crisply de ned cell borders, small and centrally placed nuclei with a homogeneous chromatin pattern, and usually without a nucleolus (Figure 21.5)

In a variety of reactive processes, the mesothelial cells undergo markedly proliferative and hyperplastic changes A relatively abundant cytoplasm is maintained, but the cell borders are less sharply de ned The nuclei are larger, both absolutely and relatively, the chromatin pattern is more hyperchromatic, and nucleoli are often present and promi-nent (Figures 21.6–21.9)

FIGURE 21.5 At higher magni cation, a sheet o relatively normal thelial cells with abundant, clear cytoplasm and crisply de ned cell borders

meso-The centrally placed nuclei are small and have a homogenous chromatin.

FIGURE 21.4 In this peritoneal wash specimen, a sheet o normal mesothelial cells has been detached.

FIGURE 21.6 This detached ragment o reactive mesothelium shows

an intact mesothelial layer with cells in two phases o the reactive cess shown in Figures 21.7, 21.8.

pro-FIGURE 21.7 The reactive mesothelial cells rom the le t side o Figure 21.6 have abundant cytoplasm, and the nuclei are larger with a more vesicular chromatin pattern Nucleoli are present but not prominent.

CHAP TER 2 1 : Se ro u s Mem bran es 589

stances is diminished by preincubating the tissue sections

in hyaluronidase is evidence that at least some of the minal hexose groups of the mucosubstances are either hyaluronic acid or chondroitin sulfate Furthermore, the fact that histochemical mucin is decreased, but not abol-ished, by incubating cells in neuraminidase before histo-chemical staining is evidence that some of the terminal carbohydrate groups are sialated (24) MacDougall et al

ter-(25) have documented that neoplastic mesothelial cells may stain with mucicarmine Negativity for the periodic acid-Schiff (PAS) reaction after sialase digestion is evi-dence that mesothelial cells lack signi cant quantities of neutral mucoproteins

FIGURE 21.8 The more reactive mesothelial cells rom the right side

o Figure 21.6 have less cytoplasm, larger nuclei with a more vesicular chromatin pattern, and more prominent nucleoli.

FIGURE 21.9 In this sheet o reactive mesothelial cells, the cytoplasm

is smaller and the nuclei are relatively larger and have a more irregular chromatin pattern.

As the hyperplastic changes in the reactive thelial cells progress, cell groups become smaller, and individual cells predominate When clustered, reactive mesothelial cells present an irregular outside border The nucleus, and especially the nucleolus, may enlarge dra-matically, but the nuclei are similar in size, shape, and pattern from cell to cell Normal mitotic gures may be seen The cytoplasm may become multivacuolated as the cells degenerate and imbibe uid (Figures 21.10–21.18)

meso-Histochemistry

Mesothelial positivity for histochemical stains that detect negative groups, such as the positively charged dye Alcian blue, is evidence of their content of acid mucoproteins

That the intensity of staining reactions for acid

mucosub-FIGURE 21.10 This individual reactive mesothelial cell has a limited amount o cytoplasm and a relatively large nucleus with a nucleo- lus The cell border is highly irregular and uzzy, consistent with the presence o the numerous elongated microvilli, which are evident on electron microscopy (see Figure 21.24) The cytoplasm is divided into

an outer less dense layer and an inner denser layer, which, turally, corresponds to the presence o intermediate laments with the characteristics o keratin (see Figure 21.25).

ultrastruc-FIGURE 21.11 Mesothelial reaction is requently associated with inf ammatory cells These reactive mesothelial cells, which are several times the size o either neutrophils or lymphocytes, are joined as a pair.

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FIGURE 21.12 These reactive mesothelial cells are loosely joined together The uppermost cell has a vacuole in the cytoplasm, which could be either a vesicle or an intracytoplasmic lumen.

FIGURE 21.13 When reactive mesothelial cells are in groups, an ular or “knobby” outside border is ormed, whereas acini orm a smooth outer border Note the “ uzzy” border on the mesothelial cell.

irreg-FIGURE 21.14 Occasionally, very reactive mesothelial cells may show cellular interactions similar to those o a keratin pearl.

FIGURE 21.16 The nucleoli o reactive mesothelial cells may be prominent.

FIGURE 21.15 Normal mitotic gures may be seen in the proli erating cells o reactive mesothelium.

FIGURE 21.17 Reactive mesothelial cells may degenerate and swell.

These three cells have abundant multivacuolated cytoplasm and large nuclei with prominent nucleoli.

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The types of terminal carbohydrate groups of brane proteins and lipids can also be characterized with lectins, which have speci c and discrete ranges of sugar group af nities Concanavalin A mesothelial cell reactivity indicates the presence of terminal groups that are either mannose or glucose

mem-Immunohistochemistry

Immunohistochemical studies of serous membranes have shown that mesothelium expresses a complex and varied phenotype with overlap of other normal tissues and many malignancies The great majority of benign mesothelial pro-liferations express several keratins, especially AE1/AE3, CK8/18 (Cam5.2), CK19, CK5/6 and CK7 that can be detected with monoclonal antibodies immunoreactive with the small, acidic, type I keratins (26) (Figure 21.19) (42)

Mesothelium does not express CK20 (27) Ovarian lial tumors express a spectrum of keratins similar to that of mesothelium (28)

epithe-Mesothelial cells frequently and preferentially express calretinin, podoplanin, HBME-1 and thrombomodulin, as well as WT-1 Vimentin and desmin are also expressed by reactive mesothelium, especially when in spindle form

Calretinin, a calcium-binding protein of 29 kDa lar to S-100 protein, is found not only in both the nucleus and the cytoplasm of reactive and neoplastic mesothelia but also in some adenocarcinomas (29–32) (Figure 21.20)

simi-Cytokeratin 5/6 is found in the cytoplasm of most thelial cells and squamous cell carcinomas, but few adeno-carcinomas (33) WT-1, a product of Wilms’ tumor gene, is found in the nucleus of reactive and neoplastic mesothelia and in ovarian surface epithelium and tumors derived there-from (34) (Figure 21.21) D2-40, an antigen characteristic

meso-of lymphatic endothelium, is also expressed by mesothelial

FIGURE 21.18 When markedly reactive mesothelial cells orm lar groups and combine with degenerating orms, they may mimic the appearance o a mucin-producing adenocarcinoma.

irregu-FIGURE 21.19 Keratin expression in mesothelium and detached thelial cells, stained with a cocktail o monoclonal antibodies (AE1/AE3).

meso-FIGURE 21.20 Calretinin Immunohistochemical staining o both nucleus and cytoplasm in benign mesothelial cells.

FIGURE 21.21 WT-1 immunoreactivity in benign mesothelium is nuclear (original magni cation 40×).

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cells with a high sensitivity (Figure 21.22), but it also marks ovarian serous carcinoma (35)

Thrombomodulin, a transmembrane glycoprotein, gives

a membranous stain in not only about half the liomas but also in some adenocarcinomas Mesothelium less frequently and less reliably expresses other antigens, including mesothelin, N-cadherin, E-cadherin, epithelial membrane antigen (EMA), Her2/Neu and EGFR (36)

mesothe-Mesothelial cells usually lack the glycoproteins detected

by antibodies to CEA, MOC-31 and BER-EP4 and the determinant detected by Leu-M1 (CD15) (37–40) Latza

et al (41) and Sheibani et al (42) reported that BER-EP4 was used to distinguish malignant epithelium (adenocarcinoma) from malignant mesothelioma, but Gaffey et al (43) and Otis (44) reported BER-EP4 immunoreactivity in high proportions

of both benign and malignant mesothelial tumors, as well as adenocarcinomas The tissue speci c nuclear transcription protein TTF-1 is important in the embryogenesis of thyroid and lungs and is found in nuclei of pneumocytes and many adenocarcinomas of the lung, but not in mesothelium (45)

Overlap between reactive and neoplastic mesothelia in the expression of even a panel of antibodies leaves only the demonstration of invasion of parietes or organs to con rm the diagnosis of malignant mesothelioma in most cases The diagnosis of mesothelioma in situ requires demonstration of invasive mesothelioma elsewhere in the same specimen or

in a subsequent specimen

The plasticity of the immunophenotype of lial cells is demonstrable in abnormal states Although mesothelium normally lacks sex steroid receptors, reactive mesothelium adjacent to endometriosis expresses focal immunoreactivity for estrogen and progesterone receptors (46) Furthermore, reactive mesothelial cells can express

mesothe-the muscle cell cytoskeleton proteins, desmin and speci c actin (47) There is experimental evidence that the pattern of intermediate lament expression by mesothe-lial cells is dependent on shape and cell–cell interaction

muscle-Induction of spindle morphology inhibits keratin synthesis

In contrast, induction of an epithelioid morphology (eg, with retinoids) stimulates keratin synthesis and inhibits vimentin synthesis; the ability of cells to respond in this manner also depends on the presence of cell–cell interac-tions (48) (Figures 21.23–21.26)

FIGURE 21.22 D2-40 immunoreactivity in benign mesothelium is dominantly membranous.

pre-FIGURE 21.23 Keratin (AE1/AE3) immunoreactivity o proli erating mesothelial spindle cells.

sub-FIGURE 21.24 A patient with severe rheumatoid arthritis and ral e usion with f orid reactive mesothelial hyperplasia o the pleura, which may be di cult to distinguish rom neoplastic proli eration The proli erating mesothelial cells may become entrapped in the brous tis- sue o organization and may mimic invasion.

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FIGURE 21.25 The reactive mesothelium in this photomicrograph is rom a hernia sac o an 18-month-old boy It is composed o proli erat- ing epithelioid cells on the sur ace and subjacent spindle-shaped cells that give the impression o proli erating broblasts.

FIGURE 21.26 The reactive peritoneum shown in Figure 21.25 is shown at higher magni cation in H&E on the le t On the right, immunohistochemical stain or keratin (AE1/AE3) illustrates that both the epithelioid and spindle cells are keratin positive, indicative o their mesothelial di erentiation.

pleura and in the visceral pleura The other organelles found

in mesothelial cells are not speci c for them Junctions of all types are found—tight junctions that serve as a barrier

to certain molecules, gap junctions for cell–cell transport, and desmosomes for cell–cell adherence Intermediate la-ments are somewhat prominent; although they do not aggre-gate into bundles, they are often arranged in a perinuclear, circumferential distribution (Figures 21.29, 21.30)

SUBMESOTHELIAL LAYER

Much of the submesothelial layer is composed of gen, elastin, and other extracellular proteins Normally, the submesothelial layer contains few cells, and most of these are broblasts, but during reactive processes, the submeso-thelial layer may become much more prominent as myo bro-blasts, in ammatory cells, and capillaries proliferate there

colla-Histochemistry

The main constituents of the submesothelial tissue are cosylated proteins, including glycosaminoglycans Since the majority of carbohydrate groups are negatively charged (as a result of an abundance of hyaluronic acid and other acidic groups), this extracellular matrix stains in a manner charac-teristic of acidic mucoproteins; that is, it is Alcian blue posi-tive That staining intensity can be diminished by treating the section with hyaluronidase before histochemical stain-ing is evidence that hyaluronic acid groups are responsible,

gly-in large part, for the gly-intensity of stagly-ingly-ing (21)

Ultrastructure

Numerous long microvilli (Figures 21.27, 21.28), ing up to 3 µm in length and 0.1 µm in diameter, are present and are more numerous in caudal portions of the parietal

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FIGURE 21.27 Mesothelial cells with their elongated microvilli, cover the sur ace o the serosa The subjacent stroma is composed o col- lagen and broblasts.

FIGURE 21.28 EM o a cluster o detached mesothelial cells within a pleural e usion Cytoplasmic lipid droplets impart a vacuolated appear- ance to some cells Note the numerous long microvilli, which impart the

“ uzzy” appearance to these cells at the light microscopic level.

FIGURE 21.29 Ultrastructure o a mesothelial cell Intermediate ments are arranged in a perinuclear distribution.

la-FIGURE 21.30 High magni cation o the luminal aspect o two thelial cells Note the small tight junction, subjacent desmosome, and the cytoskeletal laments within the microvilli.

meso-CHAP TER 2 1 : Se ro u s Mem bran es 595

Immunohistochemistry

The antigens of the submesothelial layer can be categorized into matrix constituents and antigens of the mesenchy-mal cells The extracellular matrix materials are those typi-cal of most connective tissues Types I and III collagen and bronectin are abundant Elastin bers are plentiful and basement membrane proteins, including type IV collagen and laminin, are found at the mesothelial cell–stromal interface

Proteoglycans are plentiful The pattern of intermediate lament expression by the submesothelial stromal cells var-ies with their state of excitation; quiescent cells express only vimentin, but stromal cells in regions of injury or in amma-tion also synthesize keratin detectable with antibodies to type I keratins (48)

Interactions of Mesothelial and Submesothelial Cells

The submesothelial mesenchymal cell population serves

as the anchoring substratum for the mesothelium Both mesothelial and submesothelial cells contribute to the extracellular proteins that comprise the matrix Up to 3%

of the total protein synthesized by mesothelial cells are lagens and laminin

col-Whether submesothelial cells serve as a source of mesothelial cell renewal, either in normal development, or

in conditions of rapid mesothelial cell turnover, is a troversial topic Earlier ultrastructural and kinetics studies, using thymidine incorporation, suggested that stromal cells contribute to the repopulation of denuded mesothelium (49,50) This scheme is consistent with the observation that submesothelial cells, when stimulated to proliferate, synthesize keratin and assume a more epithelioid morphol-ogy However, later studies have demonstrated that healing

con-of injured serosa is usually accomplished by multiplication and migration of surface mesothelial cells at the edges of the wounded area (51)

REACTIVE MESOTHELIUM

The capacity for mesothelial and submesothelial cellular elements of serous membranes to react and proliferate to produce morphologic patterns mimicking neoplasia is well known and is frequently a source of diagnostic confusion with malignancy The process may be diffuse or localized (Figure 21.28) Mesothelial hyperplasia in herniorrhaphy or hydro-coele specimens is well described (52) and may be nodular, demonstrate nuclear atypia and frequent mitotic gures, and

be accompanied by spindle cell elements Amin (53) recently reviewed the differential diagnosis of paratesticular mesothe-lial hyperplasia, adenomatoid tumors and other histologically similar lesions Bolen, Hammar, and McNutt (54) showed that normal surface mesothelium expressed high- and low-molecular weight cytokeratins and scattered submesothelial cells expressed vimentin, but not keratin However, reac-

tive, non-neoplastic submesothelial cells co-expressed low- molecular weight cytokeratin and vimentin

Reactive mesothelial cells have also been reported in mediastinal lymph nodes by Brooks et al (55), Parkash

et al (56), and Argani and Rosai (57), but the mechanisms

by which they enter lymphatics and survive in the sinuses

of nodes are not known This rare event may produce a dif cult differential diagnosis Clear demonstration of the mesothelial phenotype of these cells excludes metastatic carcinoma, but Sussman and Rosai (58) showed that meso-thelioma may present as a lymph node metastasis There-fore, follow-up may be the only way to make the distinction between reactive benign mesothelial cells and metastatic malignant ones (Figures 21.31, 21.32)

An uncommon manifestation of mesothelial tion is the psammoma body—a laminated calci ed structure that most likely arises through concentric calci cation fol-lowing cell death Psammoma bodies are usually nonspeci c because they may be observed in in ammatory processes

prolifera-FIGURE 21.31 Internal mammary lymph node with large epithelioid cells in the sinuses ound during coronary artery bypass gra t surgery

in a 61-year-old man No pleural lesion was present.

FIGURE 21.32 Immunohistochemical stain or keratin (AE1/AE3) onstrates the epithelioid cells singly and in groups They were negative

or CEA, Leu-M1, BER-EP4, and B72.3 and hence were considered tive mesothelial cells.

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TABLE 21.1

Reactive versus Neoplastic Mesothelium

Reactive Neoplastic Proli eration Zonal Di use Capillaries “Sunburst” Random Stromal expansion Flat Nodular

meso-Reactive versus Neoplastic Mesothelium

Serous membranes are covered by mesothelial cells, which may show a broad range of reactive changes overlapping those of malignant mesotheliomas, which are usually rela-tively low grade, well-differentiated malignancies In 2000, Churg et al (59) described the characteristics which distin-guish reactive mesothelium from neoplastic mesothelium

as zonation with the most cellular and atypical proliferation adjacent to the surface and the proliferation of capillaries perpendicular to the pleural surface in a “sunburst” pattern

in reactions Reactive mesothelium also lacked nodular expansion of the stroma, tumor necrosis, sarcomatous foci and, most signi cantly, invasion of stroma, see Table 21.1

At that time, there was no reliable immunohistochemical discriminant between reactive and neoplastic mesothelia, and they concluded that invasion was the most reliable fea-ture to diagnose mesothelioma

Nevertheless, a need for distinguishing the two entities persists, especially on cytologic or small biopsy samples, where invasion is not evident Numerous reports of immu-nostains, singly and in combination, have been used Among

them, Wu et al (60) described the use of antibodies to XIAP, X-linked inhibitor of apoptosis protein, a member of the caspase family of apoptosis inhibitors, on mesothelium

They reported no staining on normal mesothelium, staining

on 8% of reactive mesothelium and on 80% of mas, but staining was also observed on other malignancies, especially ovarian carcinomas in which 100% staining was observed Sato et al (61), used two antibodies to CD146,

mesothelio-a cell mesothelio-adhesion molecule, on effusions mesothelio-and found nocytochemical staining on all 23 mesotheliomas with one

immu-or the other antibody, but no staining on reactive cases

Hasteh et al (62) reported that immunocytochemical ing with a panel of antibodies staining positively for EMA, p53, and GLUT-1 and negatively for desmin was associated with mesothelioma and the reverse was true for reactive mesothelium Kato et al (63) used immunohistochemistry for the identi cation of GLUT-1, a protein from a family of glucose transporters, which facilitates the entry of glucose into cells; in all 40 malignant mesotheliomas, the plasma membranes were immunostained in a linear pattern, and none of the reactive mesothelial cases were immunos-tained However, Monaco et al (64) compared GLUT-1 immunostaining with uorescence in situ hybridization (FISH) testing for the p16 deletion and found the latter to

stain-be more sensitive and speci c

The p16 gene, which encodes the cyclin-dependent kinase 4 inhibitor, CDKN2A, is deleted in most mesothelio-mas The use of FISH to detect this deletion in mesothelio-mas has been exploited in pleural uid and formalin- xed, paraf n-embedded tissues to distinguish normal, benign and/or reactive mesothelium, in which p16 deletion is not observed from mesotheliomas Illei et al (65) reported dele-tions in 12 of 13 mesothelioma-containing pleural uids, but none of the benign uids Chiosea et al (66) reported dele-tions in paraf n-embedded cases in 67% of pleural meso-theliomas but only 25% of peritoneal mesotheliomas and none in reactive mesothelium They also immunostained for p16 product expression and found a lack of correlation between deletion and expression Takeda et al (67) reported deletions in 35 of 40 mesotheliomas and none in adenoma-toid tumors, benign cystic mesotheliomas or reactive meso-theliomas, and Chung et al (68) detected p16 deletions in 60% of malignant pleural mesotheliomas but not in reactive mesothelium It should be noted that p16 deletions occur

in other types of malignancies and are not mesothelioma speci c, see Table 21.2 This area of investigation shows great promise, but currently, the demonstration of invasion

of stroma remains the gold standard for the distinction of reactive mesothelium from malignant mesothelium

Reactive Mesothelium versus Carcinoma

The distinction of metastatic carcinoma from reactive mesothelium is more readily accomplished by immuno-histochemistry because the antigenic makeup of meso-thelial and epithelial cells is fundamentally different

The antibodies chosen for the diagnostic pro le relate to

FIGURE 21.33 Psammoma bodies in the le t pelvic peritoneum o a 58-year-old emale.

CHAP TER 2 1 : Se ro u s Mem bran es 597

p16 deletion Absent Present

the metastatic malignancy considered in the differential diagnosis Differentiation from adenocarcinoma of the lungs is based on its characteristic expression of TTF-1, CEA, Napsin-A, MOC-31, BER-EP4, or B72.3 and their absence in reactive mesothelium Combinations of two or more mesothelial and two or more epithelial markers are often used (69–71) PAX 8 has been found useful in dis-tinguishing ovarian lesions from mesothelial lesions (72)

Endosalpingiosis and Endometriosis

Epithelial elements may be observed in glandular ments throughout the peritoneum, omentum, and within lymph nodes Such glandular structures were recognized in the early 1900s and misinterpreted by some as metastatic carcinoma, a mistake that is unfortunately still committed today Endometriosis and endosalpingiosis were expounded upon by Sampson (73–75) earlier in this century, with refer-ence to mechanisms of pathogenesis that are still debatable

arrange-Endosalpingiosis refers to glandular spaces lined by thelium similar to uterine tube epithelium, with three cell types (ciliated, secretory, and intercalated cells) (76) (Figure 21.34) On occasion, psammoma bodies are present Peri-glandular stroma containing chronic in ammatory cells is separated from epithelium by PAS-positive basement mem-brane Endosalpingiosis may be differentiated from endo-metriosis by the lack of endometrial stroma or evidence of stromal hemorrhage associated with endometriosis (77–79)

epi-This condition is seen exclusively in women and has been reported in 12.5% of omenta removed during surgery in

females A large proportion of these women have coexisting benign disease of the uterine tube The origin of the glandular inclusions is debated but is most likely either related to the

in uence of müllerian development on the peritoneal thelium (coelomic lining) or is a sequela of disease within the uterine tube resulting in extratubal growth of displaced tubal epithelium Although de nitive evidence of neoplasia arising

meso-in endosalpmeso-ingiosis has not been documented, considerable dif culty may be encountered when differentiating extra-ovarian tumor implants removed in the setting of common epithelial ovarian tumors from endosalpingiosis with cellular atypia Evaluation of the severity of epithelial atypia, mitotic activity, the presence of ciliated cells, and the presence of invasive characteristics may aid in establishing malignancy

in this setting Metaplasia in endosalpingiosis may also be a source of diagnostic dif culty—particularly mucinous meta-plasia, which may be mistaken for metastatic mucinous adenocarcinoma (Figures 21.35, 21.36)

Endometriosis may be de ned by the presence of glands lined by endometrial-type epithelium surrounded by endo-metrial stroma, outside the uterine endometrial mucosa and myometrium (80) The condition occurs most frequently

in women of childbearing age It may occur in a variety

of body sites, ranging from the pelvic peritoneum to tant organs such as lungs, kidney, and skin, but the most

dis-FIGURE 21.34 Endosalpingiosis involving the serosa o the uterus o a 56-year-old woman Serous, intercalated, and occasional ciliated cells are present, but endometrial stroma is not.

FIGURE 21.35 Endosalpingiosis involving the omentum contains cystic glands lined by mucinous epithelium with basally oriented nuclei and apical cytoplasm Periglandular stroma contains mononuclear inf am- matory cells.

FIGURE 21.36 Mucicarmine stain o mucinous change in giosis demonstrates intracytoplasmic mucin in apical cytoplasm.

598 S ECTIO N VI: Tho ra x an d Se ro u s Me m b ra n es

frequent site is the peritoneal lining of the pelvic organs (Figure 21.37) Although the histogenesis of endometrio-sis remains unclear, two general theories have been pro-posed The ectopic growth of endometrial elements may result from displacement of endometrial tissue, through local means (such as entry of endometrium into the pelvis through the uterine tubes) or via vascular routes to distant organs (73,74) Another possibility includes metaplastic change of the pelvic peritoneum along müllerian lines of differentiation (81,82) Each mechanism may play a role in the histogenesis of endometriosis

Endometriosis may appear as brown–maroon foci on the peritoneal surfaces and may be accompanied by bro-sis or adhesions Microscopically, endometrial stroma sur-rounding endometrial epithelium is present (59) Response

to hormonal in uences is often seen and may be nous with intrauterine endometrium Metaplasia occurs in both epithelial and stromal elements, similar to metaplasias encountered in the endometrium of the uterus The pres-ence of hemosiderin-laden macrophages and brosis may

synchro-be the only evidence that endometriosis had once synchro-been present However, a de nitive diagnosis of endometriosis may not be rendered unless both endometrial glands and stroma are seen

Another common type of metaplasia, more frequently observed in pregnant than in non-pregnant women, is decidual change Although usually encountered in the submesothelial layer of pelvic peritoneal surfaces, decidual change may be seen in distant sites including the serosal surfaces of the liver, spleen, diaphragm, and within lymph nodes In these locations, decidual change may be mis-taken for metastatic carcinoma or malignant mesothelioma (Figure 21.38) (82)

Multilocular Peritoneal Inclusion Cyst

Multilocular peritoneal inclusion cyst (MPIC) is a mesothelial- lined multilocular lesion that occurs almost exclusively in women The lesion usually involves the pelvis, although it

FIGURE 21.37 Endometriosis involving the peritoneum with sion into the so t tissue o the anterior abdominal wall o a 23-year-old woman Endometrial glands and stroma are present.

exten-FIGURE 21.38 Decidual change in the pelvis during pregnancy is seen

in subserosal tissue Loosely cohesive cells with abundant eosinophilic cytoplasm are present.

FIGURE 21.39 The histologic appearance o brous pleurisy ref ects its inf ammatory nature, with granulation tissue, brin, and a zonal pat- tern ranging rom active inf ammation to quiescent dense brosis.

CHAP TER 2 1 : Se ro u s Mem bran es 599

may occur in other abdominal locations, including the tum and mesentery Usually MPIC is mass forming and may attain diameters up to 20 cm Grossly, it is composed of multiple cysts, some of which may be thin walled and trans-lucent (Figure 21.40) Histologically, the septa range from thin and delicate to thickened and in amed The mesothe-lial lining ranges from single attened cells to hobnail-type cells Squamous metaplasia of the lining mesothelium may

omen-be present Some regions may resemble the cellular pattern

of an adenomatoid tumor (Figures 21.41, 21.42) (84)

The true nature of MPIC remains somewhat sial, with some authors maintaining that it is a neoplasm while others assert it is a reactive lesion that develops in response to injury or even endometriosis The original des-ignation of multicystic mesothelioma re ects the notion that the lesion is neoplastic Recurrences are frequent, although MPIC-related deaths probably do not occur (85)

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Alimentar y Tract

VII

S E C T IO N

Esophagus Hala El-Zim a ity ■ Rob e rt H Rid de ll

2 2

ARTERIAL SUPPLY 621 VENOUS DRAINAGE 621 LYMPHATIC DRAINAGE 621 INNERVATION (NERVES AND INTERSTITIAL CELLS OF CAJAL) 621

DIAGNOSTIC CONSIDERATIONS 622 Barrett’s Esophagus 622

Gastroesophageal Re lux Disease 624 Lymphocytic Esophagitis 626

Ex oliative (Sloughing) Esophagitis (Esophagitis Dissecans Super icialis) 626

Acute Necrotizing Esophagitis 626 Adenocarcinomas o the Gastroesophageal Region 626 ACKNOWLEDGMENT 627

REFERENCES 627

EMBRYOLOGY 605 Esophageal Atresia 606 Esophageal Duplication 606 Lower Esophageal Rings and Webs 607 TOPOGRAPHY AND RELATIONS 607

MACROSCOPIC/ENDOSCOPIC FEATURES 609 Glycogenic Acanthosis 609

Heterotopias 609 Esophageal Musculature 610 Lower Esophageal Sphincter 612 Gastroesophageal J unction 612 HISTOLOGY 614

Mucosa 614 Submucosa 617 Muscularis Propria 620 Serosa 620

The esophagus is initially lined by a thin layer of strati ed columnar epithelium, which proliferates to almost occlude the lumen (2) New vacuoles appear in the luminal cells of the foregut and coalesce to form a single esophageal lumen with

a super cial layer of ciliated epithelial cells (2) (Figure 22.2)

As early as 8 weeks’ gestation, and beginning in the middle third of the esophagus, ciliated cells appear These extend cephalad and caudally to almost cover the entire strati ed columnar epithelium (2–4) At approximately 10 weeks,

a single layer of columnar cells populates the proximal

and distal ends of the esophagus (2) At approximately

4 months’ gestation, the esophageal cardiac-type glands form as a result of the downward growth of these colum-nar cells into the lamina propria with subsequent prolif-eration and differentiation (3,5) They go distally as far as the oxyntic mucosa, so that similar glands can be found in the cardia Some have used this to argue that the cardia is therefore intrinsically part of the esophagus (6), although it could just as easily be interpreted that they are just present

in all mucosae proximal to oxyntic mucosa

At approximately 5 months’ gestation, strati ed mous epithelium initially appears in the middle one-third of the esophagus and extends cephalad and caudally, replac-ing the ciliated epithelium (3,4) The upper esophagus is the last area to be replaced by squamous epithelium; and,

squa-if this process of squamous replacement is not completed

at birth, there may be persistence of ciliated cells in the upper esophagus (2,4) This may progress to gastric differ-entiation resulting in the so-called “inlet patch” (discussed subsequently) (Figure 22.3)

606 S ECTIO N VII: Alim en tary Tract

These residual cells are usually short lived, being replaced

by squamous epithelium within 2 to 3 days postpartum (4,7)

However, in some patients they either persist into adult life

or there is metaplasia back to ciliated cells (8) The single layer of columnar cells is also replaced by squamous epi-thelium, although some cells may persist at birth, usually located over the esophageal cardiac glands The submuco-sal glands develop after the appearance of the squamous epithelium and are likely derived from this squamous epi-thelial layer (4,7)

Development of the gastrointestinal neuromuscular system begins at 4 weeks with neural crest cells entering the foregut and migrating rostrocaudally The myenteric plexus develops rst, followed by formation of the submu-cosal plexus 2 to 3 weeks later At about 6 weeks’ gestation, the circular muscle layer develops, followed by the devel-opment of the longitudinal layer at approximately 9 weeks’

gestation Initially, the muscularis propria consists entirely

of smooth muscles, after which striated muscles gradually develop in the upper esophagus so that by 5 months, the normal ratio and arrangement of both muscle types are established (4) Interstitial cells of Cajal appear at week 9 and become closely associated with the myenteric plexus (9) By week 14, the fetal gut has a mature appearance (9)

Developmental defects of the esophagus can be

attributed to errors in this morphogenetic sequence This includes esophageal atresia with or without tracheoesoph-ageal stula, congenital esophageal stenosis, congenital esophageal duplication and duplication cyst, congenital esophageal rings, and congenital esophageal webs

Esophageal Atresia

Esophageal atresia with or without tracheoesophageal stula

is the most common signi cant esophageal malformation, with an incidence of approximately 1 in 3500 live births

This anomaly is caused by a failure of the primitive gut to recanalize in week 8 (10) Likewise, congenital esophageal stenosis results from incomplete esophageal recanalization during the eighth week of human embryologic development (10) Congenital esophageal stenosis can be located at any level of the esophagus, but is more frequent in the distal third It appears either as a web (membranous diaphragm)

or a long segment of esophagus with a thread-like lumen ( bromuscular stenosis) As there are often inclusions of cartilage or respiratory glands embedded in the wall of the esophagus in the region of the stricture, this anomaly may also represent an incomplete separation of the respiratory bud in some cases (10) The incidence of esophageal ste-nosis is low, occurring once in every 25,000 live births (11)

Esophageal Duplication

The notochord can induce the formation of the neural tube, gastrointestinal tract, and other organ systems It has been shown experimentally that a split notochord can result in the duplication of any region of the gastrointestinal tract (1), which may include duplications of the esophagus ranging

FIGURE 22.1 Fetal esophagus (late f rst trimester) Transverse section overview o the esophagus demonstrating inner mucosal layer, middle submucosal layer, and thin outer muscle layer Note the vagus nerves lying over the esophagus.

FIGURE 22.2 Fetal esophagus (late f rst trimester) The epithelial layer

is composed o stratif ed columnar epithelium Note the lack o laris mucosae.

muscu-FIGURE 22.3 Fetal esophagus (third trimester) The epithelial layer at this stage consists o stratif ed squamous epithelium with occasional ciliated cells on the sur ace Note the individual smooth muscle cells o developing muscularis mucosae.

Lower Esophageal Rings and Webs

Congenital esophageal rings and esophageal webs are thought to result from incomplete vacuolization of the esophageal columnar epithelium during early embryonic life The congenital esophageal ring is a concentric exten-sion of the normal esophageal tissue, usually consisting of different anatomic layers including mucosa, submucosa, and sometimes muscles The location is variable, but most are found in the distal esophagus (16)

Esophageal rings may originate from incomplete olization of the esophageal columnar epithelium during early embryonic life However, they are also associated with in ammatory conditions such as scleroderma (17), and gastroesophageal re ux (18) Schatzki’s ring is the most common esophageal ring and is found in 6 to 14%

vacu-of subjects undergoing an upper gastrointestinal series

Schatzki’s ring is a mucosal ring located at the columnar junction Since it is dif cult to exactly localize the squamocolumnar junction and the lower esophageal sphincter (LES), the exact anatomic relationship between Schatzki’s ring and the squamocolumnar junction remains controversial Typically, it is associated with the proximal margin of a hiatal hernia It consists of two layers, mucosa and submucosa, having squamous epithelium on its upper surface and columnar epithelium on its lower surface (19)

squamo-The core of the ring consists of connective tissue plus bers of the muscularis mucosae without contribution from the muscularis propria

The lower muscular ring is the most proximal and is situated slightly more proximal than Schatzki’s ring, often

by a centimeter or two Some have equated the lower cular ring with the LES (20,21) Microscopically, this ring is composed of a thickened circular smooth muscle with over-lying squamous mucosa The congenital esophageal web is

mus-a thin, usumus-ally eccentric, trmus-ansverse membrmus-ane covered by normal squamous epithelium (16) These rings are usually asymptomatic but may be associated with intermittent dys-phagia, sometimes becoming progressive or associated with attacks of sudden dysphagia (22)

TOPOGRAPHY AND RELATIONS

The adult human esophagus has cervical, thoracic, and abdominal parts The esophagus begins in the neck at the cricoid cartilage, passes through the thorax within the pos-terior mediastinum, and extends for several centimeters past the diaphragm to its junction with the stomach The overall length varies with trunk length, but in adults, the average length is approximately 23 to 25 cm In practice, endoscopic distances are measured from the incisor teeth;

and, in the average male, the junction of the esophagus and stomach is generally considered to be approximately 40 cm from the incisors This length may vary from approximately

38 to 43 cm Although convenient and commonly used in practice, the use of this distance is a crude and unreliable measurement for locating the gastroesophageal junction It has been found that the esophageal length correlates with height in children (23)

The International Classi cation of Diseases (ICD) recognized three anatomic compartments traversed by the esophagus: cervical, thoracic and abdominal (Table 22.1)

ICD also arbitrarily divides the esophagus into equal thirds:

TABLE 22.1

Regions of the Esophagus, Their Boundaries and Approximate Distances From the Incisors

Anatomic Name

Esophageal Name Anatomic Boundaries

Typical Esophagectomy (Variation ++)

Cervical Upper Hypopharynx to sternal notch 15 to <20 cm Thoracic Upper

Middle Lower

Sternal notch to azygos vein Lower border o azygos vein to in erior pulmonary vein

Lower border o in erior pulmonary vein to esophagogastric junction

608 S ECTIO N VII: Alim en tary Tract

upper, middle and lower, and this has formed the basis of the UICC/AJCC and CAP schemas (Figure 22.4) (24)

Using the anatomic boundaries is far more logical than

“typical esophagectomy” which depend on the length of the esophagus, which depends largely on the patients’ height

Where we are in the esophagus at 35cms is likely very ferent in Danny DeVito and Shaquille O’Neil!

dif-Along its course, the normal esophagus has several points of constriction (Figure 22.5) These occur at the cricoid origin of the esophagus, along the left side of the esophagus at the aortic arch, at the crossing of the left main bronchus and left atrium, and where the esophagus passes through the diaphragm These constrictions may become clinically signi cant if food or pills become lodged at these sites of luminal narrowing, with the possibility of contact mucosal injury The most common sites for lodgment are at the level of the aortic arch and left atrium, where, especially

in patients with left atrial enlargement, compression may become signi cant (25–27)

Knowledge of the relationships of the esophagus with other anatomic structures is important because these rela-tionships may be directly affected by esophageal diseases such as carcinoma or diverticula Disease of adjacent struc-tures may cause local compression of the esophagus, result-ing in dysphagia or lodgement of food or pills

The cervical portion of the esophagus is in relation,

in front, with the trachea; and at the common carotid artery (especially the left, as it inclines to that side), and parts

of the lobes of the thyroid gland; the recurrent laryngeal nerves ascend between it and the trachea; to its left side is the thoracic duct

In the thoracic segment, the esophagus continues

pos-terior to the trachea to the level of bifurcation, a site for the formation of the rare midesophageal diverticula secondary to traction from in amed mediastinal lymph nodes (28) The esophagus courses posterior to the left atrium The azygos veins ascend on either side of the thoracic segment Initially, the right and left vagus nerves run lateral to the esophagus, giving branches that form plexi on the posterior and anterior

FIGURE 22.5 Relationship o the esophagus with normal esopha- geal constrictions Barium swallow

o the normal esophagus (right) demonstrates narrowing o the lumen at the sites o constriction.

15 cm

Ce rvica l s e gme nt (3 cm)

18 cm Uppe r Thora cic S e gme nt (6 cm)

24 cm Mid Thora cic S e gme nt (8 cm)

32 cm Lowe r Thora cic S e gme nt (8 cm)

40 cm

FIGURE 22.4 Esophageal segments with approximate lengths and tances rom the incisors.

dis-CHAP TER 2 2 : Es op h a g us 609

esophageal surfaces At variable sites in the lower thoracic segment, the left and right nerves course onto the anterior and posterior surfaces of the esophagus, respectively, divide

to form the anterior and posterior plexuses, and then reunite

to form the anterior and posterior vagal trunks that course down to the stomach An awareness that variations of this pattern exist is most important for the surgeon performing the now rare operation of vagotomy

The abdominal portion of the esophagus lies in the

esophageal groove on the posterior surface of the left lobe

of the liver It is short and only measures about 1.25 cm in length, and only its front and left aspects are covered by peritoneum The esophagus enters the abdomen by passing through the esophageal hiatus, which is formed by muscles

of the diaphragm and contains the phrenoesophageal ment In most cases, the muscle sling encircling the esoph-agus is formed entirely from the right diaphragmatic crus (20,22), although variations of this pattern do occur The phrenoesophageal ligament arises from the fascia of the abdominal diaphragm and divides into an ascending and a descending leaf The former passes up through the hiatus

liga-to insert approximately 2 liga-to 3 cm above the hiatus, whereas the descending leaf has a variable insertion at or below the gastroesophageal junction or even into the gastric fundus (29) The liver forms an impression on the anterior aspect

of the esophagus On the right side the junction with the stomach is smooth, whereas on the left the junction forms a sharp angle known as the incisura or angle of His

The proposed functions of the phrenoesophageal ligament include (a) assisting in maintaining the pressure differential between the thorax and the abdomen, (b) providing xation mechanisms with maintenance of the gastroesophageal junc-tion within the abdomen during episodes of increased intraab-dominal pressure, and (c) contributing to the competence

of the LES, thus representing a possible mechanism for the absence of re ux in some patients with hiatal hernias (29–31)

MACROSCOPIC/ENDOSCOPIC FEATURES

In the empty state, the esophagus has an irregular outline

as a result of the mucosa and the submucosa being thrown into longitudinal folds During endoscopy, insuf ation causes distension so that these folds may not be appreci-ated, and the mucosa is seen to be a uniform white-pink

Glycogenic Acanthosis

Glycogenic acanthosis can be seen in up to 25% of the population with the combined use of endoscopy and even barium studies (32–34) Macroscopically, glycogenic acan-thosis interrupts the uniformity of the mucosa and presents

as white nodules or small plaques on the mucosal folds, primarily in the distal one-third of the esophagus These lesions vary in size, may be up to 1 cm in diameter, and, if extensive, may coalesce to larger plaques Microscopically,

glycogenic acanthosis consists of hyperplasia of the cells of the prickle layer containing abundant glycogen Glycogenic acanthosis may resemble, and thus may be confused macro-scopically with, monilial plaques or leukoplakia Glycogenic acanthosis should be considered a variant of normal with

as yet no de ned relationship to infection or malignancy

However, there is an association with Cowden’s syndrome

Heterotopias

Heterotopias are de ned as normal tissue occurring in sites not expected for that tissue In the literature, structures accepted as esophageal heterotopias are inconsistently

de ned Esophageal cardiac-type glands and ciliated thelium have been considered as heterotopias (7,8,35,36)

epi-or as embryologic remnants (4) by some investigatepi-ors The categorization of melanocytes, Merkel cells, and endocrine cells presents a similar problem because these cells have not been regularly found in the esophagus (37,38) Melano-sis has also been described (39–41)

Gastric-type mucosa occurring in the upper one-third

of the esophagus within 3 cm of the upper esophageal sphincter is designated the “inlet patch” (4,7,35) (Figure 22.6) Macroscopically, the inlet patch typically has a deep pink, velvety appearance (35), and presents either as a sin-gle patch or, less commonly, as multiple patches of gastric mucosa situated just below the upper esophageal sphincter

Microscopically, the patch can be lined with either type glands or gastric oxyntic mucosa Helicobacter with a variable chronic in ammatory cell in ltrate is common in infected patients and re ux may facilitate their coloniza-tion (42) (Figure 22.7) Inlet patches have been found in approximately 2 to 4% of esophagi (some gures are even higher), and can be found at all ages (43,44) Nonetheless, they are often overlooked at endoscopy as they are typically small, and looking for them is often not a high priority Most

cardiac-FIGURE 22.6 Proximal esophagus Gastric body heterotopia situated slightly distal rom the esophageal origin.

610 S ECTIO N VII: Alim en tary Tra ct

patients have no symptoms referable to the inlet patch, but, the patch can be quite large and, if parietal cells are pres-ent, can become the site of small peptic erosions, ulcers, stenosis, stula, intestinal metaplasia (45), high grade dys-plasia (46,47) and adenocarcinoma (48,49)

Theories for the origin of these heterotopias include

a metaplastic change in preexisting cardiac-type glands, cell arrest where cells destined to become body mucosa remain in the esophagus rather than descend to the site of the future stomach, persistence of embryological columnar mucosa with gastric differentiation, similar to that occur-ring distally, or otherwise unexplained heterotopia (4,35)

Sebaceous glands are occasionally found in the gus (Figure 22.8) and are accepted as heterotopias (50,51)

esopha-Thyroid tissue also has been described as heterotopic tissue

in the esophagus (52) Pancreatic metaplasia is probably the most common form of metaplasia in the cardia, usually close

to the Z line, although it may also be found in Barrett’s agus and in an inlet patch (53–55) (Figure 22.9) While it has no known signi cance, if it secretes activated pancreatic juice, then it may well potentiate Barrett’s esophagus, as it

esoph-is a normal constituent of duodenal juice, the regurgitation

of which into the esophagus is involved in its pathogenesis

Endocrine tissue can be observed in pancreatic metaplasia (personal observation) but is vanishingly rare

com-FIGURE 22.8 Sebaceous glands that in this case ormed a nodule that was examined via biopsy.

CHAP TER 2 2 : Es op h a g us 611

pharyngeal constrictor muscles, both of which contribute muscle bers to the esophageal musculature (30,31) Horizontal bers from both these muscles form the upper esophageal sphincter, which manometrically is a localized zone of increased pressure measuring 2 to 4.5 cm in length (20,22,56) Together, these muscle groups act in tandem to initiate and control swallowing

The longitudinal layer originates as two bands from its origin at the cricoid cartilage The muscles sweep dor-sally where they incompletely interdigitate, leaving a bare V-shaped area (area of Laimer) exposing the underlying circular layer This area represents an area of potential weakness where a posterior pulsion diverticulum (Zenker’s

in this case.

612 S ECTIO N VII: Alim en tary Tract

diverticulum) may form Theories regarding Zenker’s ticulum center upon a structural or physiologic abnormality

diver-of the cricopharyngeus muscle (57) The circular layer diver-of the esophagus is slightly thinner than the longitudinal layer,

a pattern that is reversed from the remainder of the trointestinal tract (30,31) In the upper third, the external longitudinal layer consists of striated muscle that is readily visible on both H&E stain, and/or a variety of histochemical

gas-or immunohistochemical stains but their number ishes and nally disappear around the junction of the upper and middle thirds (31)

dimin-At the gastroesophageal junction, the esophageal tudinal layer is continuous with the outer longitudinal layer

longi-of the stomach The circular layer continues over the ach, dividing in the region of the cardia to form the middle circular and inner oblique muscle layers of the stomach

stom-The bers of the inner oblique layer pass in a sling-like manner at the incisura and cross at right angles with the more horizontally oriented bers of the middle layer, form-ing a muscular ring to which a possible sphincter function has been ascribed (30,31)

Lower Esophageal Sphincter

The LES is best de ned manometrically, where it presents

as a 2- to 4-cm zone of pressure that is higher than tric or intraesophageal pressure The distal end of the LES

intragas-de nes the muscular component of the gastroesophageal junction (56) At rest, the sphincter maintains an average pressure of 20 mm Hg (range: 10–26) (22) The function

of the LES is to keep the lumen closed during rest, thus preventing re ux, and to relax during swallowing, thereby allowing food to pass through Physiologically, a competent sphincter exists, and various changes in the musculature of the distal esophagus thought to represent such a sphincter have been described (20,58–60)

Gastroesophageal J unction

The gastroesophageal junction can be de ned ologically, anatomically, microscopically, or endoscopically (depending on one’s viewpoint), and can be considered as being either muscular or mucosal in nature The muscular gastroesophageal junction is most accurately de ned physi-ologically by manometric studies in which the distal seg-ment of the LES de nes the junction (56) Unfortunately,

physi-in disease states such as severe gastroesophageal re ux ease (GERD) or Barrett’s esophagus, the pressure may be so low as to not allow for localization by these means

dis-Anatomical landmarks that can be used to de ne the gastroesophageal junction include the peritoneal re ection from the stomach onto the diaphragm or the incisura (angle

of His) (30,31); however, their use is limited to those ing out dissections or resected surgical specimens

carry-The upper margin of the diaphragmatic indentation has been used as a guide to de ne the gastroesophageal junc-tion; however, in the presence of hiatal hernia, this demon-strates variable movement (30,31)

The mucosal gastroesophageal junction does not respond to the muscular gastroesophageal junction as

cor-de ned above; and, particularly if the mucosa is red and

in amed, it may not even be visible, but may also be the site

of Schatzki’s ring However there has been a shift in de tions The mucosal junction was considered to lie normally within the LES and at one point used to be considered to

ni-be within 2 cm of the muscular junction as de ned by the proximal edge of the gastric folds (61); thus, it was consid-ered that the distal 2 cm of the tubular esophagus could

be lined by gastric cardia-type mucosa, and it was this that led to Barrett’s esophagus originally being de ned as 3 cm

or more of glandular mucosa within the tubular esophagus,

as it ensured that at least 1 cm of mucosa should be rett’s mucosa Indeed, some of these tongues of Barrett’s esophagus fail to reveal goblet cells on initial sampling, but

Bar-in one study, 23% of these patients had goblet cells Bar-in these tongues when rebiopsied (62)

Practically, while the endoscopic de nition of the troesophageal junction differs worldwide, and all have advantages and disadvantages, (63) the most important

gas-de nition is that in which the gastroesophageal junction

is de ned as the upper limit of the proximal gastric folds This is used almost everywhere with the exception of Japan, but is affected by respiration, gut motor activity, and the degree of distension of the esophagus and stomach, all

of which can vary with the moment

The proximal margin of the gastric folds has been shown

to closely approximate the muscular gastroesophageal tion and thus may provide a xed and reasonably reproduc-ible anatomic landmark for the muscular gastroesophageal junction (61) The squamocolumnar junction should, there-fore, approximate these when the esophagus is partially dis-tended by gas The mucosal squamocolumnar junction is seen macroscopically and endoscopically as a serrated line

junc-of contrast known as the Z line or ora serrata (Figure 22.10)

The Z line consists of small projections of red gastric lium, up to 5 mm long and 3 mm wide, extending upward into the squamous epithelium Sometimes the Z line is accompanied by a ring (Schatzki’s ring) (Figure 22.11) that has squamous mucosa above and glandular mucosa distally (64,65), which is sometimes associated with dysphagia

epithe-Although extension of this gastric mucosa may be ferentially symmetric, it is often asymmetric The mucosal gastroesophageal junction may be straight rather than ser-rated, this occurring most often in the presence of a lower mucosal (Schatzki’s) ring

circum-In Japan and parts of Asia, the gastroesophageal tion is de ned by the distal end of esophageal palisade ves-sels (66,67) However, this is an approximation, as the end

junc-of these vessels can be present above, at and even below the Z line in normal individuals, and can also be obscured

by in ammation The two most commonly used landmarks are, therefore, both dubious scienti cally

In the lower esophagus, the submucosal vessels of the distal esophagus are connected to the gastric submucosal

CHAP TER 2 2 : Es op h a g us 613

vessels at the rst gastric folds by a series of vessels referred

to as longitudinal (vertical) vessels These vessels, present

in the lamina propria, are about 2 to 4 cm in length and can

be often seen through the squamous or columnar mucosa (66,68) Their lower visible limit is also supposed to mark the original site of the gastroesophageal junction so that

“shifts” in this caudally should be apparent However, in some patients, these are quite dif cult to visualize, while in others they clearly extend into the gastric rugae They may, therefore, be a less sensitive or speci c marker of Barrett’s esophagus than originally thought, so that, based on a study

of resections for esophageal squamous cell carcinoma, a minimum of 5 mm of palisaded vessels is usually required for a diagnosis of Barrett’s esophagus (69) Note that there

is no mention of intestinal metaplasia in this de nition

While this suggests that great care should be taken in ing an endoscopic diagnosis of Barrett’s esophagus without

mak-the usual biopsy con rmation, mak-there have (to date) been no studies relating this minimum criteria for Barrett’s esopha-gus with biopsies It is, therefore, unclear if one biopsied patients with minimum criteria, how many of these would have goblet cells, but almost certainly the great minority

Even in the studies cited, the endoscopic diagnosis was not con rmed histologically so that the sensitivity and other characteristics of this technique are still unclear

Microscopically, the gastroesophageal junction is the squamocolumnar junction, but it is also clear that with-out the endoscopic correlation, there is no way of knowing whether any biopsy that contains both squamous and glan-dular mucosa, the latter with or without goblet cells in the glandular mucosa, is normal or pathological

The most distal esophagus immediately below the mous mucosa is normally lined by cardiac-type mucosa that varies from a millimeter to about a centimeter The old view that this extended for 2 to 3 cm is clearly wrong, but in some patients, there is a direct transition from squamous

squa-to oxyntic mucosa The view that the length of the cardiac mucosa may be dependent on the degree of re ux is not unreasonable Some studies have demonstrated that the length of cardiac or oxyntocardiac mucosa correlates with the severity of acid re ux suggesting that this metaplastic epithelium results from acid re ux (re ux carditis) (70,71)

Because re ux is physiological, the issue of where ogy stops and pathology starts is the issue While one can use de nitions such as time the lower esophagus remains

physiol-at pH4 or less, it may be relphysiol-ative changes within the same patient that are critical

In both autopsy- and endoscopy-based studies (35, 54,70,72,73) that included pediatric patients, columnar/

cardiac mucosa was either not identi ed in up to 65% of cases, present as a short segment of less than 1.0 cm., com-bined with oxyntic or oxyntocardiac mucosa, or demon-strated considerable circumferential variation within indi-viduals The authors suggest either that (a) cardiac mucosa

of the gastroesophageal junction is not normal (but rather acquired) and that only squamous (esophageal) and oxyntic (stomach) mucosa are normal for this region or (b) it is a

614 S ECTIO N VII: Alim en tary Tract

physiologic response to gastroesophageal re ux; but, either way it develops in response to a stimulus that includes some degree of acid re ux So again it becomes a matter

of semantics as to whether one regards re ux as pathologic

or physiologic One could also argue that the normal ologic position of the anal sphincter is to be closed, but it would cause all sorts of problems if it remained that way permanently! Conversely, it is dif cult to see what useful function permitting gastroesophageal re ux serves except that other sphincters (eg, pylorus) also re ux with some degree of frequency, which may have a physiologic bene-

t in aiding digestion (as well as predisposing to Barrett’s esophagus)

HISTOLOGY

The wall of the esophagus consists of four layers: mucosa, submucosa, muscularis propria, and adventitia Unlike other areas of the gastrointestinal tract, the esophagus does not have a distinct serosal covering This allows esophageal tumors to spread more easily and make them harder to treat surgically (74) The missing serosal layer also makes lumi-nal disruptions more challenging to repair

Mucosa

The mucosa consists of a nonkeratinizing, strati ed mous epithelium, lamina propria, and muscularis mucosae (Figure 22.12)

squa-Epithelium

The squamous epithelium can be divided into basal, prickle, and super cial cell layers The basal layer occupies approxi-mately 5 to 15% of the epithelium, being one to three cells thick; however, in the distal 3 cm, approximately 60% of normal individuals without objective or subjective evidence

of gastroesophageal re ux may show basal cell sia of greater than 15% (75,76) The upper extent of the basal zone has been arbitrarily de ned as the level where the nuclei are separated by a distance equal to their diam-eter (77) Periodic acid-Schiff (PAS) stain may be used to demonstrate the upper extent of the glycogen-poor basal cells (Figure 22.13) Above the basal cell layer, the prickle and super cial cell layers consist of glycogen-rich cells that become progressively atter toward the surface The glandular mucosa of the distal esophagus is typical cardiac mucosa with variable numbers of specialized gastric cells and cardiac glands

hyperpla-Within the squamous mucosa a variety of other cell types exist These include:

Melanocytes, likely originally reported as argentaf n or argyrophil cells, have been reported in between 3 and 8% of esophagi (39,78,79) Clinically these can form aggregates and be visible as “melanosis esophagi” (80) The presence of melanocytes, referred to as melanosis (39,40,81), accounts for the occurrence of primary melanoma of the esophagus (82,83) and one possible blue nevus (78)

Merkel cells have not only both endocrine markers (chromogranin A, synaptophysin, etc) but also immunoreac-tivity with CK20 and Cam5.2 However, the evidence that these cells exist at all is very limited CK20 immunoreactive cells were not found in the developing esophagus in one study (84) while in one small systematic study they were found to be most concentrated in the midesophagus; CK20 immunoreactive cells were also found in 2/6 small cell car-cinomas, perhaps not surprisingly (37) Argyrophilic positive endocrine cells are almost certainly melanocytes or Merkel cells (37,38), although the rare occurrence of pure small cell carcinoma may arise from these cells (85)

Endocrine cells Cells that were originally described to

be endocrine because of their argyrophilia, were almost certainly melanocytes, while those with endocrine mark-ers immunohistochemically were likely Merkel cells (v.s.)

FIGURE 22.12 Midesophagus The esophageal mucosa consists o a sur ace epithelial layer, middle lamina propria, and lower muscularis mucosae, which consists o longitudinally oriented smooth muscle bundles.

FIGURE 22.13 Midesophagus The basal cell layer o the esophageal epithelium shows lack o glycogen, allowing or ready distinction rom the overlying glycogen-rich cells (PAS).

in the epithelium close to the lamina propria and in the ina propria (86) Intraepithelial antigen-presenting cells can

lam-be demonstrated using S-100 or MHC2 IELs are CD8+ and are normal, but it is virtually impossible to distinguish IELs and APCs in routine sections, and they are therefore collec-tively perhaps best called intraepithelial mononuclear cells

Occasional lymphocytes are a normal nding in the epithelium and are usually located in a suprabasal loca-tion (87–89) As they interdigitate between the epithelial cells, their nuclei become convoluted and may be confused with the nuclei of neutrophils The term squiggle cell, or intraepithelial cells with irregular nuclear contours, is used

to describe this appearance (Figure 22.14) As in the rest of the gastrointestinal tract, IELs are CD3+/CD8+, indicating suppressor/cytotoxic function Langerhans cells, which are S-100+, CD6+, and CDla+, also are located in a suprabasal location (Figure 22.15); they function as antigen-presenting cells, similar to Langerhans cells of the skin (87,88)

Cytology specimens of the esophagus have strati ed squamous epithelium, gastric-type epithelium representing the distal 1 to 2 cm, and contaminants from the oropharynx, respiratory tract, and foreign materials such as food particles

Squamous epithelium in cytologic material consists dominantly of super cial and intermediate squamous cells, with the deeper parabasal cells or squamous “pearls” occa-sionally observed Gastric-type epithelium from the lower

pre-1 to 2 cm of the esophagus is brushed as cohesive fragments

of uniform cells displaying a honeycomb arrangement The peripheral cells of the cluster are attened The nuclei are

regular and paracentrally situated and contain a few ules of chromatin and occasionally a small nucleolus

gran-The electron microscopic appearance of the epithelial layer demonstrates similarities to nonkeratinizing squamous epithelium elsewhere (Figure 22.16) The cuboidal basal cells are attached to the basement membrane by hemi-desmosomes Progressing super cially, the epithelial cells become more attened and the nuclei more pyknotic (87)

FIGURE 22.14 A Numerous lymphocytes within the esophageal epithelium, some o which have a “squiggle”

appearance (arrows) In addition, the intercellular spaces are dilated causing very prominent prickles, while some o these have ormed small “bubbles” primarily at the junction between epithelial cells (best seen in the upper right quadrant) Care needs to be taken not to include perinuclear vacuolization/cytoplasmic retraction

or paranuclear vacuoles as dilated intercellular spaces B Intraepithelial lymphocytes are o T-cell origin, as demonstrated using T-cell markers, and are primarily suppressor (CD3+ CD8+) cells.

FIGURE 22.15 Langerhans cell (arrow) in a suprabasal position (S-100).

616 S ECTIO N VII: Alim en tary Tract

Cell processes and desmosomes are most extensive in the prickle cell layer, becoming fewer and more simpli ed super- cially (90) Membrane-bound, acid phosphatase–contain-ing structures measuring 200 to 300 nm in diameter are identi ed within the epithelial cells and are postulated to have a lysosomal function, possibly involved in the digestion

of cell junctions necessary for epithelial sloughing (90,91)

Cell kinetics of the human esophagus have not been studied extensively The basal cells are responsible for epi-

thelial regeneration; and, although data on human geal mucosal renewal are not available, epithelial turnover

esopha-in the esophagus is slower than that esopha-in the small bowel (92)

In mice, basal cell proliferation has been shown to have

a circadian rhythm (93), and the epithelial turnover time

in the normal rat esophagus is approximately 7 days (94)

In patients with GERD, there is an increased proliferative activity of the basal cells, resulting in basal cell hyperplasia (95)

Stem cells in the esophagus consist of a single basal layer of cells attached to the basement membrane that lie between the papillae (interpapillary basal cells) and have a low proliferative activity, being almost entirely Ki-67 nega-tive (Figure 22.17) In animal models, when these cells divide, one remains attached to the basement membrane, while the other migrates and differentiates They, therefore, have a high proliferative capacity, divide relatively infre-quently in vivo, and are phenotypically “primitive.” Under experimental conditions, such stem cells “home” to dam-aged esophagus, while it can also be shown that bone mar-row–derived cells can also home to the esophagus and dif-ferentiate into esophageal stem cells, including squamous epithelium (96) As such, basally situated stem cells do not show differentiation characteristics, possessing a different immunophenotype from the more differentiated cells in being CK13 immunoreactive; CK13 is expressed at high levels in the cells of both the papillary basal layer (PBL)

FIGURE 22.16 Scanning electron micrograph o the sur ace geal mucosa in which intercellular junctions are readily appreciated.

esopha-A

B

FIGURE 22.17 Basal layer o esophagus immunostained with MIB-1 A The basal cell layer is relatively thin and unstimulated, consisting o only about three cell layers Many o the cells in the basal layer are completely unstained, there ore, representing likely stem cells, while the proli erating cells with black nuclei are in the cell layer immediately above B In this biopsy, the basal layer is much thicker and, there ore, more proli erative, and there are ewer noncycling stem cells in the basal layer.

CHAP TER 2 2 : Es op h a g us 617

and epibasal layers but is absent from the keratinocytes of the interpapillary basal layer (IBL) In addition, CK14 and CK15 are patchy in the IBL, which contrasts with the high levels of expression in the PBL and epibasal layers Also, mRNA for the differentiation marker CK4 is detectable in the papillary region from the second epibasal layer onward but does not appear in the interpapillary region until the third epibasal layer (97,98) Therefore, IBL cells appear to

be the least differentiated cell type in the tissue (98) basal integrin expression is a consistent nding at the tips

Supra-of the esophageal papillae, so PBL cells probably migrate

to this site (99) This concept is illustrated in Figure 22.18

Lamina Propria

The lamina propria is the nonepithelial portion of the mucosa above the muscularis mucosae; it consists of areolar con-nective tissue and contains vascular structures, scattered

in ammatory cells, and mucus-secreting glands In adults, the presence of scattered in ammatory cells, including lym-phocytes and plasma cells, is considered a normal nding and does not correlate with acid re ux (77) Lymphocytes identi ed in the lamina propria are both CD4+ and CD8+, with the T4 population predominating (87) Immunoglobu-lin (Ig)A-producing B-cells (plasma cells) predominate with

a smaller population of IgG- and IgM-producing B-cells (plasma cells) (87) Finger-like extensions of lamina propria, termed papillae, extend into the epithelium, with the maxi-mum depth of extension allowable in the normal esophagus

varying from 50 (100) to 75% (100,101) Practically, it is easy to use the “rule of thirds” when examining biopsies, in which papillae should not extend into the upper one-third, and basal cells should not get higher than half way up the basal one-third [adapted from: Ismail-Beigi et al (76)] In the distal 3 cm of the esophagus, up to 60% of individu-als without objective evidence of re ux demonstrate papil-lary lengths that may exceed these values (75) Conversely, increasing basal cell hyperplasia and papillary height does correlate with increasing severity of re ux (102)

Esophageal cardiac-type glands are diffusely scattered

in the lamina propria through all levels of the esophagus, predominating in the distal and proximal regions (4,35)

While they have been variably considered as heterotopias (7,35), normal constituents, or embryologic remnants, there is little doubt that they perform a lubricating function and are physiologically necessary to facilitate bolus passage

However, their number is highly variable, and they are not always identi ed in the esophagus, having been found in 1 to 16% of esophagi in various studies (7,35,79) Histologically, these glands are located within the lamina propria, resem-ble the cardiac glands of the stomach, and are composed of cells secreting neutral mucins (Figure 22.19) They resem-ble pyloric glands, even to the extent that they are MUC6 immunoreactive, and may contain variable numbers of both parietal and chief cells and Paneth-like lysozyme-producing granules Their ducts are lined by simple mucus-producing cells, in contrast to the submucosal gland ducts, which are frequently squamous lined These duct-lining cells may also extend onto the surface for a variable distance, even producing small islands of simple mucus-producing islands with an abrupt junction with squamous mucosa (H Wata-nabe, personal communication)

Muscularis Mucosae

The muscularis mucosae is composed of smooth muscle bundles oriented longitudinally (56), rather than having both a circular and a longitudinal arrangement as in the stomach and intestines The muscularis mucosae begin

at the cricoid cartilage of the pharynx and become thicker distally At the gastroesophageal junction, the esophageal muscularis mucosae is thicker than that of the stomach and may be so thick as to be mistaken for muscularis propria

on biopsy (Figure 22.20) This thicker appearance, along with the longitudinal arrangement, is used sometimes to indicate an esophageal origin for the biopsy, and the dif-ferences between the muscularis mucosae of the stomach and esophagus can be used to identify the muscular gastro-esophageal junction Following ulceration of the mucosa, the epithelium and muscularis mucosae both regenerate forming a double muscularis mucosae that is so character-istic of Barrett’s esophagus

li erative and intermediate in behavior between IBL and epibasal cells (see text) Di erentiated squamous cells are shown in orange (Modif ed with permission rom Seery JP, Watt FM Asymmetric stem-cell divisions def ne the architecture o human oesophageal epithelium Curr Biol 2000;10:1447–1450.)

618 S ECTIO N VII: Alim en tary Tra ct

lymphatics, and submucosal glands (Figure 22.21) The submucosal glands are considered to be a continuation of the minor salivary glands of the oropharynx and are scat-tered throughout the entire esophagus, but they are more concentrated in the upper and lower regions (4)

Submucosal glands consist of mucous cells, with or out a minor serous component, and produce acid mucins (Figure 22.22) as well as bicarbonate, which may have a local protective effect The glands are drained by ducts, ini-tially lined by a single layer of cuboidal epithelium, becoming

FIGURE 22.19 Midesophagus A Esophageal cardiac-type glands are located within the lamina propria The ducts are lined by gastric oveolar–like cells B The duct-lining cells may extend over the stratif ed squamous epithelium or variable distances (PAS-D) C, D The glands stained PAS-D positive and Alcian blue at pH 2.5 negative, characteristic o neutral mucins.

CHAP TER 2 2 : Es op h a g us 619

strati ed squamous in type, which penetrate the laris mucosae and epithelium to open into the esophageal lumen This duct epithelium has been immunohistochemi-cally shown to be CK14+/CK19+/CK7+/CK8/18+/variable CK20+ (103) This pro le is similar to normal esophageal squamous epithelium and multilayered epithelium (ME), the latter representing a possible intermediate or early stage of Barrett’s esophagus (103) Microscopic periductal aggre-

muscu-gates of chronic in ammatory cells and duct dilatation are not uncommon ndings in the normal esophagus (104) The presence of submucosal glands is indicative of an esophageal origin because these glands are not present in the stomach;

unfortunately, submucosal glands are almost never present in mucosal biopsy specimens However, the ducts of the glands may be seen in the lamina propria of mucosal biopsies but are still only demonstrable in up to 14% of biopsies from the lower

FIGURE 22.20 Distal esophagus The mucosal layer at the esophageal junction is characterized by muscularis mucosae that is thicker than the muscularis mucosae o the more proximal esophagus (compare with Figure 22.12) Note the esophageal cardiac-type gland situated above the muscularis mucosae.

gastro-FIGURE 22.21 Midesophagus Submucosal glands o the esophagus are located within the submucosa just beneath the muscularis mucosae Peri- ductal and periglandular chronic in ammation can be a normal f nding

Note that in contrast to the columnar-lined glands o the lamina propria, the ducts o the submucosal glands are lined by squamous epithelium.

A

C

D B

FIGURE 22.22 Midesophagus A The submucosal glands are composed predominantly o mucus-secreting cells with a variable serous component B and C The submucosal glands stained positive with PAS-D and Alcian blue at pH 2.5, a characteristic o acid mucins D Submucosal glands may demonstrate oncocytic metaplasia.

620 S ECTIO N VII: Alim en tary Tract

esophagus (105,106) Esophageal intramucosal ticulosis is said to arise from postin ammatory obstruction of the ducts with subsequent duct dilatation (104,107)

pseudodiver-Muscularis Propria

It is generally stated that as much as the upper quarter to upper one-third of the proximal muscularis propria is com-posed of striated muscles (30,31); however, only a short length (approximately 5%) of the proximal muscularis pro-pria is composed only of striated muscle (108) Immediately distal to this, smooth and striated muscles intermix, with smooth muscles predominating, whereas slightly more than 50% of the distal muscularis propria is composed solely of

smooth muscles (108) (Figure 22.23) Despite the ence of these two different muscle types, they can function

pres-as a unit Auerbach’s plexus with its pres-associated interstitial cells of Cajal is found between the two muscle layers, while the interstital cells are also present in the muscularis pro-pria Disease processes may preferentially involve only one

of the muscular layers, as in scleroderma (in which atrophy predominantly involves the circular layer) or in achalasia (in which the circular layer may become hypertrophied) (4)

pro-CHAP TER 2 2 : Es op h a g us 621

peritoneum, respectively (4) The majority of the gus is surrounded by fascia, which condenses around the esophagus, forming a sheath-like structure In the upper mediastinum, the esophagus is given support as this fascial tissue extends out to surround and form a similar sheath-like arrangement around adjacent structures (30,31)

esopha-ARTERIAL SUPPLY

The cervical portion of the esophagus is supplied by branches of the inferior thyroid artery with contribution from various intercostal arteries Branches of the bronchial arteries, intercostal arteries, and aorta supply the thoracic segment, whereas the abdominal segment is supplied

by branches of the left gastric and inferior phrenic artery (4,30,31,109) Branches from these arteries run within the muscular layer, giving rise to branches that course within the submucosa Anastomoses are extensive, explaining the rarity of esophageal infarction (4,109)

VENOUS DRAINAGE

The venous return from the upper two-thirds of the agus drains into the inferior thyroid vein and azygos sys-tem, eventually reaching the superior vena cava The lower esophageal segment drains into the systemic system through branches of the azygos vein and left inferior phrenic vein

esoph-The lower esophageal segment also drains into the portal system from branches of the left gastric vein and through the short gastric veins that empty into the splenic vein (4,30,31,109)

The anatomy of the lower esophageal system has been shown to consist of four layers (110) Radially arranged intraepithelial channels drain into the super cial venous plexus, which is found in the upper submucosa This super- cial venous plexus, consisting of three to ve main trunks located in the lower submucosa, communicates with the deep intrinsic veins Perforating veins connect this layer with the adventitial layer of veins located on the esophageal surface The venous system appears to be mainly distrib-uted within the esophageal mucosal folds (67)

The portal and caval systems communicate through the esophageal and gastric submucosal veins; and, with increased blood ow, as occurs in portal hypertension, all the venous channels of the normal esophagus dilate and are referred to as varices In portal hypertension, varices are complicated by ulceration and rupture with hemorrhage It has been suggested that a major variceal hemorrhage occurs

as a result of rupture of a varix of the deep intrinsic veins, whereas minor variceal hemorrhages occur as a result of rupture of a varix in the super cial venous plexus or even from the intraepithelial channels (110)

LYMPHATIC DRAINAGE

A rich network of lymphatics in the lamina propria and submucosa connects with lymphatics in the muscular and adventitial layers Lymphatics in the muscular layer are pre-dominantly oriented in a longitudinal direction (4) In view

of this longitudinal arrangement, extensive intramucosal and submucosal spread beyond a grossly visible tumor is not uncommon This becomes an important consideration when assessing resection margins at frozen section

In general, the cervical esophagus drains into the nal jugular and upper tracheal lymph node groups The thoracic esophagus drains into the superior, the middle, and the lower mediastinal lymph node groups, whereas the abdominal segment drains into superior gastric, celiac axis, common hepatic artery, and splenic artery lymph nodes (111) Despite this drainage pattern, in practice the exten-sive communication of lymphatics results in a varied and unpredictable metastatic pattern (111)

inter-INNERVATION (NERVES AND INTERSTITIAL CELLS OF CAJAL)

The esophagus receives both parasympathetic and thetic nerve supplies containing afferent and efferent bers that innervate glands, blood vessels, and muscles of the esophagus The vagus nerve carries both parasympathetic and some sympathetic bers Sympathetic bers originat-ing in cervical and paravertebral chains run with vascular structures and end at the esophagus

sympa-As in the rest of the gastrointestinal tract, the esophagus has an intrinsic innervation system This consists of ganglion cells in the submucosa (Meissner’s plexus) and between the circular and longitudinal muscle layers (Auerbach’s plexus)

These plexuses are less well developed in the esophagus when compared with the remainder of the gastrointestinal tract, and the density of neurons increases as one proceeds toward the stomach (30,31) The submucosal plexus is less well developed than the myenteric nerve plexus

The plexuses of the esophagus receive input from ganglionic sympathetic and preganglionic and postgangli-onic parasympathetic bers, as well as from other intrinsic ganglion cells (22) Three cell types are described in the plexuses (108) Type I neurons are multipolar and con ned

post-to Auerbach’s plexus, and their axons establish synapses with type II cells Type II neurons are more numerous, are multipolar, and are found in both Auerbach’s and Meiss-ner’s plexuses These cells supply the muscularis propria and muscularis mucosae and stimulate secretory activity

Interstitial cells of Cajal (ICC) are widely distributed within the submucosal, intramuscular, and intermuscular layers associated with the terminal networks of sympa-thetic nerves In the few studies that have examined the

622 S ECTIO N VII: Alim en tary Tract

distribution of ICCs in the esophagus, they have been identi ed in the distal one-third of the esophagus in close association with smooth muscles, as well as in the mid-dle one-third associated with both smooth and striated muscles (112) Gastrointestinal stromal tumors (GISTs), including those of esophageal origin, originate from these ICCs Peculiar to the esophagus, when compared to the rest of the gastrointestinal tract, is that tumors of stromal origin are more frequently benign leiomyomas rather than GISTs (113), although they have a readily identi able component of ICCs so are more likely hamartomas

Regulatory peptides identi ed within nerve bers and around smooth muscle bundles include vasoactive intesti-nal peptide (VIP), substance P, enkephalin, and neuropep-tide Y (NPY) (114,115) Nerve bers containing VIP and NPY are the most abundant types present in the esophagus, and the pattern of innervation by these peptide-containing neurons differs from that in the stomach and small intestine (116) Cholecystokinin (CCK) receptors are found in both the mucosa and nerves of the cardia (117)

DIAGNOSTIC CONSIDERATIONS

Commonly received biopsy specimens from the esophagus are for the diagnosis of re ux esophagitis or Barrett’s esoph-agus The problems of interpretation present in these cases involve the mucosal changes occurring primarily within the con nes of the LES

Barrett’s Esophagus

In North America, and much of the rest of the world, the diagnosis of Barrett’s requires two components

(a) an endoscopic demonstration of a proximal shift in the

Z line (ie, an abnormal endoscopic appearance)(b) the presence of glandular mucosa either with goblet cells (intestinal metaplasia) on biopsy in much of the world, including North America(63) and parts of Europe, or irrespective of the presence of goblet cells (UK), the lat-ter primarily on the assumption that all Barrett’s have goblet cells at some point, and are, therefore, all likely

measurement) and the most proximal limit, the maximum

“M” measurement So a patient with a total of 5 cm Barrett’s esophagus of which the lower 3 cm is circumferential is a C3M5 Barrett’s (119) Barrett’s esophagus demonstrates a red velvety mucosa corresponding to the columnar epithelium, with an apparent focal or diffuse cephalad migration of the Z

junction (Figure 22.24) Barrett’s mucosa merges tibly with the gastric mucosa distally The junction with the esophageal squamous epithelium may appear as a symmetric

impercep-or asymmetric Z line (as at the nimpercep-ormal gastroesophageal tion) or as islands of columnar mucosa alternating with the squamous epithelium (“island pattern”) Foci of squamous epithelium are occasionally identi ed within Barrett’s mucosa

junc-In amed squamous mucosa may be indistinguishable from Barrett’s mucosa endoscopically, and, therefore, also from the squamo-Barrett junction, when both are present

However, while historically Barrett’s esophagus is divided into long (>3 cm) and short segments (up to 3 cm), some also use ultrashort (<1 cm) While Barrett’s esopha-gus has to have a whole spectrum of endoscopic length and can be circumferential or have tongues, or both, where

sub-an irregular Z line stops sub-and Barrett’s esophagus starts is a major issue In one study it was clear that while endosco-pists looking at videos had good interobserver variability for

BE overall, that when the length of BE was less than 1 cm, there was little agreement.(119) This is a major issue, for the endoscopist should not be asking “is this Barrett’s?” but,

“there is an endoscopic appearance here that is Barrett’s esophagus unless the biopsies are squamous, what sort of glandular mucosa is present and is there any evidence of dysplasia?” However, if it is unclear whether the endoscopic appearances are those of Barrett’s esophagus or not, while the question is still relevant, the interpretation is problem-atic Dysplasia cannot be ignored, but intestinal metaplasia could just as easily represent metaplasia in the cardia as part of gastric disease, which may or may not be grounds for follow-up Practically therefore, while ultrashort Barrett’s esophagus has to exist, it is almost impossible to diagnose due to lack of reproducibility of the endoscopic criteria

Histological Appearances and Integration with Endoscopic Appearance

Multiple de nitions have been used for what de nes

Bar-FIGURE 22.24 Gastroesophageal region Barrett’s esophagus, onstrating proximal extension o columnar-lined mucosa well into the tubular esophagus This columnar-lined mucosa extends more than 2

dem-cm rom the proximal gastric olds (arrows).

CHAP TER 2 2 : Es op h a g us 623

in USA as “the condition in which any extent of metaplastic columnar epithelium that predisposes to cancer develop-ment replaces the strati ed squamous epithelium that nor-mally lines the distal esophagus”; presently this requires the presence of intestinal metaplasia (63) (Figure 22.25) This does not parallel the de nition in UK (118) that removes the need for goblet cells to diagnose Barrett’s esophagus In

UK, the presence of columnar metaplasia alone in the distal esophagus of a patient with the typical endoscopic abnormal-ity de nes Barrett’s esophagus, the assumption being that all columnar mucosa have goblet cells somewhere (118)

In UK, it is called Barrett’s esophagus or columnar-lined esophagus, and one states whether goblet cells are present

or not (118) With both de nitions, the diagnosis of Barrett’s esophagus is, therefore, primarily endoscopic, biopsy being used to con rm the diagnosis and to ensure as far as possible that dysplasia or carcinoma is not already present Indeed,

in many countries, including much of North America and Europe, clinicians and pathologists are uncomfortable with the UK de nition (120), but are much more con dent in making the diagnosis if goblet cells are present

In North America, intestinal metaplasia is (currently) perceived as the only type of columnar epithelium that clearly predisposes to malignancy, and although others might, the evidence is less strong, and also “the inclusion

of patients with cardia-type epithelium under the rubric of

“Barrett’s esophagus” would substantially increase the ber of patients with that disorder, which would substan-tially increase treatment costs” (63), an interesting reason for justifying a de nition The de nition also suggests that while non-intestinalized mucosa cannot be called Barrett’s

num-esophagus, it offers no alternative, so that “columnar-lined esophagus” may be the best alternative

The important implication of this de nition is that patients with apparent non-goblet cell Barrett’s esopha-gus are likely also at increased risk of adenocarcinoma, so should not be lost to surveillance or follow-up (8,121–124)

The rst (diagnostic) endoscopy is, in practice, the rst veillance endoscopy, so appropriate biopsies are required

sur-The presence and extent of columnar-lined epithelium in biopsies should, therefore, be stated, if only for complete-ness The presence or absence of goblet cells in biopsies should also be stated

This de nition poses problems because patients from the rst decade of life on may not show goblet cells with overt endoscopic Barrett’s esophagus In these patients as well as those with overt tongues of Barrett’s mucosa, there

is no name to give them The issue is whether patients out goblet cells are at risk of developing carcinoma, and if

with-so what that risk is The data suggest that a strong case can be made for viewing patients without goblet cells as being at similar risk of those with goblet cells (122) How-ever, although this view was not embraced in the US 2011

de nition, the important thing is that patients with Barrett’s mucosa without goblet cells are not lost to follow-up

In some biopsies, esophageal columnar–lined epithelium cannot easily be distinguished from mucosa arising from the

“normal” gastric cardiac mucosa The distinction between esophageal columnar-lined epithelium as well as Barrett’s intestinal metaplasia from the gastric cardia with and with-out intestinal metaplasia can be suggested on morphological grounds (125–129) Biopsies taken from the esophagus are

A

B

FIGURE 22.25 Barrett’s esophagus A Intestinal metaplasia is nized by the presence o goblet cells Incomplete intestinal metapla- sia (lower hal o gland) is characterized by goblet cells associated with gastric oveolar–like columnar cells, whereas complete intes- tinal metaplasia (upper hal o the gland) is characterized by goblet cells associated with small intestinal, absorptive-like columnar cells

recog-B Goblet cells in intestinal metaplasia stain positive with Alcian blue

at pH 2.5 It is not recommended to do this either routinely or or nostic purposes.

624 S ECTIO N VII: Alim en tary Tract

more likely to show crypt atrophy and disarray (125,127), and can be compared with a typical biopsy of the architectural distortion seen in typical ulcerative colitis Cardiac mucosa tends to exist in regular islands rather than diffuse atrophy

The lamina propria in esophageal (Barrett’s) epithelium either have larger spaces between glands, or have more atro-phy and in ammation than that encountered in the cardia (127) The best clue for the mucosa coming from Barrett’s mucosa is the presence of submucosal esophageal glands

or their ducts, as generally they are not present in the dia (129) Also, the muscularis mucosae is much thicker in the esophagus and is separated from the basal epithelium in the esophagus by an epithelium-free layer of lamina propria (129) Intestinal metaplasia in Barrett’s is usually extensive with a villiform surface, a pattern rarely seen in the cardia (129) Barrett’s epithelium with intestinal metaplasia is usu-ally characterized by an absence of enterochromaf n cells although pancreatic metaplasia may be seen (129)

car-Multilayered epithelium (MLE) is a distinctive type of epithelium histologically characterized by multiple layers of basaloid cells with an overlying layer of columnar epithe-lium (Figure 22.26) This epithelium has been shown to have mucin and immunohistochemical qualities similar to normal squamous epithelium, duct gland epithelium, and Barrett’s epithelium (103); and it is associated with re ux-induced injury (130) and intestinal metaplasia in patients with Barrett’s disease (131) As such, it is postulated that multilayered epithelium may represent an early/transi-tional phase of columnar metaplasia in Barrett’s esophagus, although some believe that this is ciliated ultrastructurally and, therefore, represents simple metaplasia or persistent fetal epithelium (36,132)

Gastroesophageal Reflux Disease

The problems encountered in GERD are related to mous epithelial changes in the distal 3 cm of the esophagus and to the signi cance of intraepithelial in ammatory cells

squa-Reactive Squamous Changes

Re ux-associated squamous hyperplasia (RASH) consists of basal cell hyperplasia of greater than 15% and extension of the papillae into the upper one-third of the epithelium (76) (Figure 22.27) Practically, in well-oriented biopsy samples, the esophageal mucosa can be divided into thirds; the papil-lae should not be seen extending into the upper one-third, and the basal cell layer should not extend more than half way into the lower one-third This is operatively a simple and rapid technique for assessing the degree of RASH However, similar changes have been described in the distal 3 cm of the esophagus in approximately 60% of patients without objec-tive or subjective evidence of acid re ux (75); thus, if pres-ent in biopsy samples originating from this zone, such hyper-plastic changes should be considered normal, despite the fact that these changes are much more likely to be found in patients with GERD and NERD (nonerosive re ux disease) (102) Changes of RASH are much more likely to be a more speci c indicator of re ux if the biopsy samples are taken above the distal 3 cm of the esophagus (75,77) It should

be remembered that squamous hyperplasia is a reaction to any form of esophageal injury and needs to be interpreted in light of the clinical context

Dilated Intercellular Spaces

Apart from squamous hyperplasia, dilatation of the cellular spaces of the squamous epithelium as a result of gastroesophageal re ux has been demonstrated at both the electron and the light microscopic level (133–135) (Fig-ure 22.14) This early epithelial damage is morphologically characterized by irregular dilatation of the intercellular spaces of the basal and prickle cell layers in both erosive and

inter-FIGURE 22.26 Multilayered epithelium, in which there is apical mucin production at the luminal sur ace (top), but the remainder o the epithe- lium appears squamous with intercellular bridges.

FIGURE 22.27 Re ux esophagitis Basal cell hyperplasia and ening o the papillae are present The papillae have extended almost to the sur ace o the mucosa (arrows).