Ebook Atlas of anatomic pathology Part 2

Part 2 book Atlas of anatomic pathology presentation of content: Neurogenic tumors, soft tissue tumors of the mediastinum, germ cell tumors, lymphoproliferative disorders. Invite you to consult Part 2 book Atlas of anatomic pathology presentation of content: Neurogenic tumors, soft tissue tumors of the mediastinum, germ cell tumors, lymphoproliferative disorders. Invite you to consult

S Suster (ed.), Atlas of Mediastinal Pathology, Atlas of Anatomic Pathology,

DOI 10.1007/978-1-4939-2674-9_4, © Springer Science+Business Media, LLC 2015

Neurogenic tumors of the mediastinum are relatively rare

and are most often encountered in the pediatric-age

popula-tion They most commonly arise from structures in the

pos-terior mediastinum, although they can originate from all

three mediastinal compartments Neurogenic tumors are, in

fact, the most common tumors of the posterior mediastinum

in both children and adults Neurogenic tumors can be of

neuroblastic origin or may arise from peripheral nerve sheath

elements (Table 4.1 ).

4.1 Neuroblastic Neoplasms

Neuroblastic neoplasms (Figs 4.1 , 4.2 , 4.3 , 4.4 , 4.5 , 4.6 , 4.7 , 4.8 , 4.9 , 4.10 , 4.11 , 4.12 , 4.13 , 4.14 , 4.15 , 4.16 , 4.17 , 4.18 , 4.19 , 4.20 , 4.21 , 4.22 , 4.23 , 4.24 , 4.25 , 4.26 , 4.27 , 4.28 , 4.29 , 4.30 , 4.31 , and 4.32 ) arise from primitive precursor cells of the sympathetic nervous system They are the most common solid tumors in children under 1 year of age, although they can also occur in older children and in adults Some cases can be associated with neurofi bromatosis (NF1) They show

a histologic spectrum that ranges from very well- differentiated and mature neuronal elements to tumors com- posed of primitive and poorly differentiated cells, mimicking the entire spectrum of neuroblastic maturation

Malignant peripheral nerve sheath tumor

Fig 4.1 Neuroblastic tumors are most often large and solid, well

cir-cumscribed, and surrounded by a fi brous capsule They usually show a smooth outer surface This image is an example of a ganglioneuroma, the most common benign tumor originating from the thoracic sympa-thetic nerves

Fig 4.2 Ganglioneuromas are benign neurogenic tumors composed of

mature neural elements admixed in varying proportions They are often

paucicellular and show a variously collagenized stroma on scanning

magnifi cation

Fig 4.3 On higher magnifi cation, ganglioneuromas are composed

mainly of loose, fi brocollagenous stroma admixed with bland- appearing

fi broblastic or schwannian spindle cells The stroma may vary from

loose and edematous to densely collagenized Based on the extent of the

schwannian component, they have been classifi ed into schwannian

stroma dominant (“mature” ganglioneuroma) and schwannian stroma

poor (“maturing” ganglioneuroma)

( center ) containing large ganglion cells with abundant cytoplasm and

round nuclei that are intimately admixed in various proportions with the spindle cells and collagenous stroma

of large ganglion cells with abundant granular eosinophilic cytoplasm and large, round nuclei

4 Neurogenic Tumors

Fig 4.6 Schwannian stroma-rich mediastinal ganglioneuroma shows

clusters of large ganglion cells with small, round nuclei surrounded by

abundant granular eosinophilic cytoplasm embedded in a dense

collag-enous stroma containing abundant schwannian spindle cells

Fig 4.7 Higher magnifi cation of schwannian stroma-rich

ganglioneu-roma showing large ganglion cells with eccentric nuclei

Fig 4.8 Higher magnifi cation of ganglion cells in ganglioneuroma

showing characteristic small nuclei surrounded by abundant pink ular cytoplasm The number of ganglion cells in these tumors may vary;

gran-if they are very sparse, proper identgran-ifi cation may require a diligent search

Fig 4.9 Ganglioneuroblastoma is a tumor characterized by an

admix-ture in various proportions of both maadmix-ture schwannian and ganglionic elements, as well as primitive neuroblastic elements that form discrete nests or islands of tumor cells The tumors are grossly well circum-scribed, with a fl eshy, tan-white cut surface with focal areas of cystic degeneration and foci of calcifi cation

4.1 Neuroblastic Neoplasms

bland-appearing schwannian spindle cells ( left ) percolating between

small nests of small neuroblastic cells ( right )

paucicellular, collagenous stroma merging imperceptibly with islands and nests of primitive, small neuroblastic cells admixed with larger gan-glionic cells

Fig 4.10 Histologically, ganglioneuroblastoma shows areas that are

indistinguishable from ganglioneuroma in association with foci of

neu-roblastic elements The neuneu-roblastic elements are arranged in discrete,

small nests of primitive neuroblastic cells ( lower right ) that merge with

the schwannian-rich stroma ( left )

Fig 4.13 Higher magnifi cation of schwannian stroma-poor

ganglio-neuroblastoma shows a mixed cell population composed of small, itive neuroblastic cells admixed with larger ganglionic cells

prim-4 Neurogenic Tumors

small nests containing neuroblastic elements surrounded by a

schwannian- rich spindle-cell stroma

Fig 4.15 Higher magnifi cation of ganglioneuroblastoma showing a

mixed population of neuroblastic small cells admixed with larger

gan-glionic cells with abundant eosinophilic cytoplasm

cations Neuroblastoma elements occasionally undergo dystrophic calcifi cation that replaces the tumor cells The presence of these foci of calcifi cation is an indication of a neuroblastic component in the tumor and should prompt search of additional sections

Fig 4.17 Neuroblastoma is the most common malignant neoplasm of

the posterior mediastinum in children, particularly under the age of 1 year Grossly, the tumors are well circumscribed and encapsulated, with

a multinodular outer surface 4.1 Neuroblastic Neoplasms

Fig 4.18 Cut surface of a neuroblastoma shows grayish white, soft

tissue with areas of hemorrhage and necrosis and foci of calcifi cation

Fig 4.19 Histologically, neuroblastoma is composed of a

prolifera-tion of small, round blue cells showing various degrees of organizaprolifera-tion

Neuroblastomas have been classifi ed into differentiating, poorly

differ-entiated, and undifferdiffer-entiated, depending on their degree of maturation

and organization The well-differentiated tumors (differentiating

neuro-blastoma) overlap with ganglioneuroblastoma but show a

predomi-nance of neuroblastic elements over ganglionic cells and may also

contain a minor schwannian component The poorly differentiated

vari-ants show no evidence of ganglionic or schwannian differentiation and

grow as sheets of small tumor cells that often present a nested

appear-ance, as in this example

islands or nests of tumor cells separated by a vascular stroma

Fig 4.21 Higher magnifi cation showing well-defi ned nests of tumor

cells with abundant fi brillary eosinophilic material (neuropil) in the background The fi brillary material (neuropil) is a distinctive feature of neuroblastic neoplasms and helps in the differential diagnosis with other small, round cell tumors

4 Neurogenic Tumors

Fig 4.22 Another area in the same tumor shows a peculiar linear,

single-fi le arrangement of neuroblastic cells embedded in abundant

fi brillary matrix, a feature often observed in these tumors

Fig 4.23 Extensive stromal calcifi cation is a common feature in

neu-roblastoma The calcifying process can be so extensive as to obscure the

underlying neoplastic proliferation; recognition of the tumor cells may

then require extensive sampling

Fig 4.24 Higher magnifi cation in calcifying neuroblastoma shows

irregular deposits of calcifi c material surrounded by proliferation of primitive, small, round blue cells

Fig 4.25 Higher magnifi cation shows small nests of tumor cells

admixed with calcifi c stromal deposits The tumor cells show a tive appearance with small, round nuclei with tiny nucleoli and no dis-cernible cytoplasm

primi-4.1 Neuroblastic Neoplasms

Fig 4.26 Another example of differentiating neuroblastoma on

scan-ning magnifi cation shows a lobular growth pattern separated by well-

vascularized stroma and foci of stromal calcifi cations

Fig 4.27 Higher magnifi cation shows a lobule of tumor cells with

abundant background neuropil and a mixed cell population, including

ganglionic-type large cells and scattered smaller neuroblastic cells

Fig 4.28 High power shows a scant amount of tumor cells displaying

various degrees of maturation, fl oating in abundant eosinophilic fi lary matrix (neuropil)

almost solid sheets of small, round, primitive cells with only a vague hint of nesting

4 Neurogenic Tumors

a primitive population of small, round, blue cells growing as sheets with

scattered mitoses The tumor cells have small, irregular nuclei with

scant nuclear detail and small nucleoli

Fig 4.31 Higher magnifi cation shows the presence of Flexner-type

rosettes, another distinctive feature sometimes seen in poorly

differenti-ated neuroblastoma

Fig 4.32 Immunohistochemistry can aid in the differential diagnosis

of neuroblastoma, particularly the poorly differentiated and

undifferen-tiated forms Neuron-specifi c enolase ( pictured ) and other neuronal

markers (synaptophysin, chromogranin, neurofi lament protein, etc.) are generally positive in the tumor cells, to the exclusion of other specifi c markers of differentiation (keratins, desmin, actin, S-100 protein, etc.) Molecular genetics also plays a role, as alterations such as overexpres-

sion of MYCN and chromosome 1p deletion have been associated with

more aggressive behavior and can serve as markers for the more poorly differentiated tumors

4.1 Neuroblastic Neoplasms

4.2 Peripheral Nerve Sheath Tumors

Peripheral nerve sheath tumors (PNSTs) are the most

com-monly encountered tumors in the posterior mediastinum

These can also show a wide spectrum of differentiation

rang-ing from benign, fully differentiated neural tumors

(schwan-noma, Figs 4.33 , 4.34 , 4.35 , 4.36 , 4.37 , 4.38 , 4.39 , 4.40 ,

4.41 , 4.42 , 4.43 , 4.44 , 4.45 , 4.46 , 4.47 , 4.48 , 4.49 , 4.50 , 4.51 ,

4.52 , 4.53 , 4.54 , 4.55 , 4.56 , 4.57 , 4.58 , and 4.59 ) to tumors showing a prominent fi broblastic component (neurofi broma, Figs 4.60 , 4.61 , 4.62 , and 4.63 ) to poorly differentiated malignant neural neoplasms (malignant PNSTs, Figs 4.64 , 4.65 , 4.66 , 4.67 , 4.68 , 4.69 , 4.70 , 4.71 , 4.72 , 4.73 , 4.74 , 4.75 , and 4.76 ) The tumors most often affect young to middle- aged adults and are commonly seen in a paravertebral loca- tion Some tumors may adopt a dumbbell confi guration and penetrate into the spinal canal

Fig 4.33 Schwannoma is the most common type of peripheral nerve

sheath tumor (PNST) of the mediastinum Although nearly all are seen

in the posterior mediastinum, they can also present as anterior

medias-tinal masses Grossly, the tumors are encapsulated and well

circum-scribed The cut surface is characterized by tan, homogenous, somewhat

lobulated tissue with areas of cystic degeneration

spindle- cell proliferation that is completely surrounded by a fi brous

capsule

Fig 4.35 The spindle cells in schwannoma form fascicles that can

intersect at right angles Two growth patterns are recognized: (1) Antoni

type A ( illustrated ), characterized by closely packed tumor cells, and

(2) Antoni type B, characterized by loosely arranged spindle cells rated by abundant myxoid or edematous stroma

Fig 4.36 Higher magnifi cation from Antoni type A area of

schwan-noma shows tightly packed spindle cells forming fascicles that appear

to cross at right angles

4 Neurogenic Tumors

Fig 4.37 Higher magnifi cation from Antoni type A area of

schwan-noma shows small spindle cells with dispersed chromatin and tapered

nuclei surrounded by dense collagenous stroma The cells tend to adopt

a “wavy” appearance as they weave through the surrounding collagen

fi bers

schwannoma shows a well-circumscribed and encapsulated tumor with

strikingly edematous stroma

Fig 4.39 Higher magnifi cation from an Antoni type B area in

medias-tinal schwannoma shows areas of stromal collagenization alternating with areas displaying prominent stromal edema

Fig 4.40 Higher magnifi cation from an Antoni type B area in

medias-tinal schwannoma shows a sparse spindle-cell proliferation separated

by abundant edematous and myxoid stroma 4.2 Peripheral Nerve Sheath Tumors

spin-dle to stellate cells devoid of cytologic atypia fl oating in a lightly

myx-oid stroma

Fig 4.42 Schwannomas can contain admixtures of Antoni type A and

Antoni type B areas within the same tumor

Fig 4.43 Another striking feature of Antoni type A schwannomas is

the focal presence of so-called Verocay bodies, composed of a striking palisading of the spindle-cell nuclei around areas of densely eosino-philic basement membrane deposition

Fig 4.44 Foci of Antoni type A with Verocay bodies can also be

ran-domly scattered within otherwise typical Antoni type B areas in schwannomas

4 Neurogenic Tumors

Verocay bodies in a small focus of Antoni type A schwannoma

Fig 4.46 Another important feature of schwannoma is perivascular

cuffi ng of hyalinized collagen around the vessels, which can be

observed in both Antoni type A and type B areas

Antoni type B areas of schwannoma, where it can affect groups of sels adopting a plexiform appearance

of a vessel surrounded by a cuff of dense, fi brinous eosinophilic material

4.2 Peripheral Nerve Sheath Tumors

Fig 4.49 Another striking feature of schwannoma is cystic

degenera-tion of the tumor, resulting in a multilocular cystic appearance This

appearance is more frequently seen in Antoni type B areas, but it also

may affect Antoni type A tumors

Fig 4.50 Higher magnifi cation of a cystic area in mediastinal

schwan-noma shows cystically dilated space containing bland spindle cells in

its walls

lipidized stroma Numerous large, foamy macrophages are seen spersed with the spindle cells in the stroma

abun-dant foamy macrophages (xanthoma cells) scattered between the dle cells

spin-4 Neurogenic Tumors

Fig 4.53 A common feature in schwannomas is the occasional

pres-ence of degenerating, atypical cells with enlarged, hyperchromatic, and

sometimes multilobulated nuclei that can harbor intranuclear

inclu-sions Such cells are the result of a degenerative process (so-called

“ancient” schwannoma) and should not be construed as evidence of

malignancy

Fig 4.54 Schwannomas can also show striking cellularity, with mild

to moderate cytologic atypia raising the suspicion for malignancy Such

tumors have been designated “cellular” schwannoma and may be very

diffi cult to separate from a low-grade malignant schwannoma A

help-ful clue to the diagnosis is the good circumscription and complete

encapsulation of the tumor; malignant neoplasms are almost always

infi ltrative and will not show a complete, well-formed capsule

sur-rounding the lesion This example shows a thick, fi brous capsule

com-pletely surrounding a fl eshy, hemorrhagic tumor

Fig 4.55 Scanning magnifi cation of a cellular schwannoma shows

dense spindle-cell proliferation surrounded by a thick, fi brous capsule

Fig 4.56 Higher magnifi cation of cellular schwannoma shows

densely packed, hyperchromatic spindle cells with scattered mitoses

( center ) Mitotic activity of up to 4 mitoses per 10 high-power fi elds can

be seen in these tumors A diagnosis of cellular schwannoma requires the absence of tumor cell necrosis and capsular invasion

4.2 Peripheral Nerve Sheath Tumors

Fig 4.57 Schwannomas in the mediastinum can also be associated

with heavy pigment deposition (“melanotic schwannomas”) An

unusual form of melanotic schwannoma associated with the familial

complex of cardiac myxomas and Cushing’s syndrome has been

desig-nated as “psammomatous melanotic schwannoma.” The tumors are

characterized by a schwannian spindle-cell proliferation with heavy

cytoplasmic melanin pigment deposition, scattered psammoma bodies

and scattered mature adipocytes

mediastinum in a patient with Carney’s complex shows large,

concen-tric foci of stromal calcifi cations It is important to identify patients

with this condition, as melanotic schwannomas are associated with

malignant behavior in approximately 10 % of patients with this

syndrome

Fig 4.59 Typical schwannomas are usually straightforward and easy

to diagnose Unusual cases may require immunohistochemistry The schwannoma in this image shows nuclear and cytoplasmic positivity with S-100 protein and is negative for most other differentiation anti-gens, such as desmin, smooth muscle antigen (SMA), cytokeratins, and glial fi brillary acidic protein (GFAP) S-100 protein positivity is lost with progressive loss of differentiation, so strong positivity for this marker strongly suggests a tumor is benign, even if it is highly cellular

or has marked cytologic atypia

Fig 4.60 Neurofi bromas in the posterior mediastinum are usually

associated with nerve trunks and can cause a fusiform expansion of the involved nerves Unlike schwannomas, they may not always have a cap-sule but usually present as well-circumscribed lesions Multiple or plexiform, multinodular lesions are associated with neurofi bromatosis (NF1) and have a high potential for malignant transformation The cut surface is a homogeneous tan-white color with a striking plexiform or multinodular appearance

4 Neurogenic Tumors

Fig 4.61 Histologically, neurofi bromas are composed of an

admix-ture of Schwann cells and fi broblastic cells embedded in a collagenous

matrix The scanning magnifi cation in this example shows a striking

plexiform pattern The stroma can show prominent myxoid changes,

but perivascular hyalinization, cystic degeneration, and palisading of

nuclei are not features seen in these tumors

Fig 4.62 Higher magnifi cation of mediastinal neurofi broma The

tumor cells show oval to spindled nuclei with dispersed chromatin and

absence of nucleoli or mitotic activity The stroma characteristically

displays scattered, short bundles of collagen fi bers that resemble

shred-ded carrots

Fig 4.63 Neurofi bromas can show prominent myxoid stromal changes

characterized by deposition of abundant light-staining mucosubstances

in the interstitium Staining of the tumor cells for S-100 protein can be helpful in distinguishing these tumors from other spindle-cell neo-plasms with prominent myxoid changes

Fig 4.64 Malignant peripheral nerve sheath tumors (PNSTs) are the

malignant counterparts of schwannoma and neurofi broma (“malignant schwannoma” and “neurogenic sarcoma” of the old literature) Grossly, they are characterized by large, bulky, and infi ltrative tumors that may

or may not retain remnants of a preexisting capsule On the cut surface, the tumors are hemorrhagic, with areas of necrosis and cystic degeneration

4.2 Peripheral Nerve Sheath Tumors

Fig 4.65 Histologically malignant PNSTs are characterized by a

fas-cicular spindle-cell proliferation that shows a “marbled” appearance:

fascicles composed of tightly packed spindle cells ( dark areas )

alter-nate with fascicles containing a more sparse spindle-cell population

( light areas )

Fig 4.66 On higher magnifi cation, malignant PNSTs show an

atypi-cal spindle-cell population characterized by enlarged, dark nuclei with

a condensed chromatin pattern and scattered mitotic fi gures ( center )

Nuclear pleomorphism can vary widely, from minimal to striking with

pleomorphic and anaplastic tumor cells

because S-100 protein will stain only scattered, isolated tumor cells, as

in this image In fact, strong and diffuse positivity for S-100 protein in

a spindle-cell sarcoma must be regarded as suspect when trying to establish a diagnosis of malignant PNST; it may indicate a cellular schwannoma

Fig 4.68 Another distinctive feature of malignant PNSTs is a well-

developed herringbone pattern of growth, characterized by thin, gated fascicles of tumor cells from which shorter branches of spindle cells emanate at 45° angles

elon-4 Neurogenic Tumors

Fig 4.69 Higher magnifi cation of the herringbone pattern in a

malig-nant PNST shows tightly wound fascicles of atypical spindle cells that

appear to be emanating from central spines This pattern can also be

commonly observed in monophasic synovial sarcoma, which represents

the main histologic differential diagnosis for malignant PNSTs

Fig 4.70 Higher magnifi cation of the herringbone pattern in a

malig-nant PNST shows cytologically atypical spindle cells with a dense

chro-matin pattern and mild nuclear pleomorphism with scattered mitotic

fi gures

Fig 4.71 Another distinctive feature commonly observed in

malig-nant PNST is prominent cuffi ng of small vessels in the tumor by the tumor cells The spindle tumor cells are layered circumferentially around the adventitia, and atypical epithelioid cells replace the intima and the vessel wall

Fig 4.72 Malignant PNSTs are frequently accompanied by extensive

areas of necrosis The areas of necrosis are irregular (“geographic”) and can occupy large portions of the tumor

4.2 Peripheral Nerve Sheath Tumors

Fig 4.73 The areas of necrosis in malignant PNSTs often adopt a

peritheliomatous distribution: small nests of tumor cells surround a

small vessel and are separated from the rest of the tumor by intervening

areas of necrosis

Fig 4.74 An unusual histologic variant of malignant PNST is

charac-terized by the epithelioid appearance of the tumor cells Epithelioid

malignant schwannomas usually display a lobular, plexiform pattern of

growth on scanning magnifi cation

Fig 4.75 Higher magnifi cation of epithelioid malignant PNST shows

concentric layering of epithelioid tumor cells around a small vessel, with some retraction artifact from the surrounding stroma

Fig 4.76 High-power magnifi cation of epithelioid malignant PNST

shows a rather monotonous population of round to oval tumor cells with vesicular chromatin and prominent nucleoli surrounded by abundant lightly eosinophilic cytoplasm These tumors tend to display stronger and more diffuse positivity for S-100 protein than the more conven-tional, spindle-cell form of malignant PNST

4 Neurogenic Tumors

4.3 Primitive Neuroectodermal Tumor

(Extraskeletal Ewing’s Sarcoma)

Primitive neuroectodermal tumors (PNETs, Figs 4.77 , 4.78 ,

4.79 , and 4.80 ) represent the extraosseous, soft tissue

coun-terpart of Ewing’s sarcoma of bone They may rarely occur

in the mediastinum The tumors are characterized by a

recur-rent, balanced translocation involving the EWRS1 gene on chromosome 22; they are members of the ETS family of tran-

scription factors

Fig 4.77 Histologically, primitive neuroectodermal tumors (PNETs)

are composed of sheets of primitive, small, round, blue cells that can

show varying degrees of neuroectodermal differentiation

Fig 4.78 The tumor cells show lack of organization, but can

some-times form small pseudorosettes ( circle ) simulating neuroblastoma

Fig 4.79 On higher magnifi cation, the tumor cells of PNET show

uni-form small, round nuclei with a dense chromatin pattern and scant eosinophilic cytoplasm, which is often periodic acid-Schiff (PAS) posi-tive The tumor cells in some cases may be larger, with oval nuclei and prominent nucleoli Distinction from undifferentiated neuroblastoma is best accomplished with molecular studies to demonstrate absence of

MYCN amplifi cation and the presence of an EWRS1 gene translocation

with detection of one of the characteristic fusion partners

Fig 4.80 Immunohistochemical staining also can be helpful in the

diagnosis of PNET by demonstrating strong cytoplasmic or nous positivity for CD99 Other markers that can be focally or sporadi-cally expressed in these tumors include cytokeratin, neuron-specifi c enolase (NSE), CD57, and synaptophysin

membra-4.3 Primitive Neuroectodermal Tumor (Extraskeletal Ewing’s Sarcoma)

Suggested Reading

Adam A, Hochholzer L Ganglioneuroblastoma of the posterior

medi-astinum: a clinicopathologic review of 80 cases Cancer

1981;47:373–81

Ambros IM, Ambros PF, Strehl S, Kovar H, Gadner H, Salzer-Kuntschik

M MIC2 is a specifi c marker for Ewing’s sarcoma and peripheral

primitive neuroectodermal tumors Evidence for a common

histo-genesis of Ewing’s sarcoma and peripheral primitive

neuroectoder-mal tumor from MIC2 expression and specifi c chromosoneuroectoder-mal

aberration Cancer 1991;67:1886–93

Cardillo G, Carleo F, Khalil MW, Carbone L, Treggiari S, Salvadori L,

et al Surgical treatment of benign neurogenic tumours of the

medi-astinum: a single institution report Eur J Cardiothorac Surg

2008;34:1210–4

Carney JA Psammomatous melanotic schwannoma: a distinctive

heritable tumor with special associations, including cardiac

myx-omas and Cushing’s syndrome Am J Surg Pathol 1990;14:

206–22

Chalmers AH, Armstrong P Plexiform mediastinal neurofi bromas A

report of two cases Br J Radiol 1977;50:215–7

Chatten J, Shimada H, Sather HN, Wong KY, Siegel SE, Hammond

GD Prognostic value of histopathology in advanced

neuroblas-toma: a report from the Childrens Cancer Study Group Hum Pathol

1988;19:1187–8

Dehner LP Primitive neuroectodermal tumor and Ewing’s sarcoma

Am J Surg Pathol 1993;17:1–13

Cataldo D Mediastinal ganglioneuroma: a rare and often asymptomatic

tumor Chir Ital 2005;53:403–5

Ducatman BS, Scheithauer BW, Piepgras BG, Reiman HM, Ilstrup

DM Malignant peripheral nerve sheath tumors A clinicopathologic

study of 120 cases Cancer 1986;57:2006–21

Hirschfeld K, Woodward W Neurofi bromata of the anterior

mediasti-num Aust N Z J Surg 1963;33:76–7

Inoue M, Mitsudomi T, Osaki T, Oyama T, Haratake J, Yasumoto

K Malignant transformation of an intrathoracic neurofi broma in

von Recklinghausen’s disease Scand Cardiovasc J 1998;32:

173–5

Johnson MD, Glick AD, Davis BW Immunohistochemical evaluation

of Leu-7, myelin basic protein, S-100 protein, glial fi brillary acidic

protein, and LN3 immunoreactivity in nerve sheath tumors and

sar-comas Arch Pathol Lab Med 1988;112:155–60

Joshi VV, Cantor AB, Altshuler G, Larkin EW, Neill JS, Shuster JJ,

et al Recommendations for modifi cation of terminology of

neuro-blastic tumors and prognostic signifi cance of Shimada classifi

ca-tion A clinicopathologic study of 213 cases from the Pediatric

Oncology Group Cancer 1992;69:2183–96

King RM, Telander RL, Smithson WA, Banks PM, Han MT Primary

mediastinal tumors in children J Pediatr Surg 1982;17:

512–20

Koezuka S, Hata Y, Sato F, Otsuka H, Makina T, Tochigi N, Iyoda

A Malignant peripheral nerve sheath tumor in the anterior tinum: a case report Mol Clin Oncol 2014;2:987–90

Manduch M, Dexter DF, Ellis PM, Reid K, Isotalo PA Extraskeletal Ewing’s sarcoma/primitive neuroectodermal tumor of the posterior mediastinum with t(11;22)(q24;q12) Tumori 2008;94:888–91 Marchevsky AM Mediastinal tumors of peripheral nervous system ori-gin Semin Diagn Pathol 1999;16:65–78

Pekmeczi M, Reuss DE, Hirbe AC, Dahiya S, Gutmann DH, von Deimling A, et al Morphologic and immunohistochemical features

of malignant peripheral nerve sheath tumors and cellular nomas Mod Pathol 2014 doi: 10.1038/modpathol.2014.109 [Epub ahead of print]

Schweigert M, Meyer C, Wolf F, Stein HJ Peripheral primitive ectodermal tumor of the thymus Interact Cardiovasc Thorac Surg 2011;12:303–5

Shields TW, Reynolds M Neurogenic tumors of the thorax Surg Clin North Am 1988;68:645–68

Shirakusa T, Tsutsui M, Montonaga R, Takata S, Yoshomine K, Kondo

K, Yoshida T Intrathoracic tumors arising from the vagus nerve Review of resected tumors in Japan Scand J Thorac Cardiovasc Surg 1989;23:173–5

Steffanson K, Wollmann R, Jerkovic M S-100 protein in soft tissue tumors derived from schwann cells and melanocytes Am J Pathol 1982;106:261–8

Sugio K, Inoue T, Inoue K, Tateishi M, Ishida T, Sugimachi

K Neurogenic tumors of the mediastinum originated from the vagus nerve Eur J Surg Oncol 1995;21:214–6

Suster S Recent advances in the application of immunohistochemical markers for the diagnosis of soft tissue tumors Semin Diagn Pathol 2000;17:225–35

Takeda S, Miyoshi S, Minami M, Matsuda H Intrathoracic neurogenic tumors–50 years’ experience in a Japanese institution Eur J Cardiothorac Surg 2004;26:807–12

Torres-Mora J, Dry S, Li X, Binder S, Amin M, Folpe AL Malignant melanotic schwannian tumor: a clinicopathologic, immunohisto-chemical, and gene expression profi ling study of 40 cases, with a proposal for the reclassifi cation of “melanotic schwannoma” Am J Surg Pathol 2014;38:94–105

Turc-Carel C, Aurias A, Mugneret F, Lizard S, Sidaner I, Volk C, et al Chromosomes in Ewing’s sarcoma I An evaluation of 85 cases of remarkable consistency of t(11;22)(q24;q12) Cancer Genet Cytogenet 1988;32:229–38

Weitzner S Adjacent malignant schwannoma and neurofi broma of intrathoracic vagus Am Surg 1976;42:866–70

Wick MR, Swanson PE, Scheithauer BW, Manivel JC Malignant peripheral nerve sheath tumor An immunohistochemical study of

62 cases Am J Clin Pathol 1987;87:425–33

Woodruff JM, Godwin TA, Erlandson RA, Susin M, Martini N Cellular schwannoma: a variety of schwannoma sometimes mistaken for a malignant tumor Am J Surg Pathol 1981;5:733–44

4 Neurogenic Tumors

S Suster (ed.), Atlas of Mediastinal Pathology, Atlas of Anatomic Pathology,

DOI 10.1007/978-1-4939-2674-9_5, © Springer Science+Business Media, LLC 2015

Mesenchymal tumors of the mediastinum are relatively rare,

yet virtually all types of mesenchymal neoplasms have been

described in this location (Table 5.1 ).

Soft Tissue Tumors

of the Mediastinum

5

Table 5.1 Mesenchymal tumors of the mediastinum

Lymphangioma Epithelioid hemangioendothelioma Angiosarcoma Fibroblastic/fi brohistiocytic

tumors

Solitary fi brous tumor Malignant solitary fi brous tumor

Malignant fi brous histiocytoma (undifferentiated sarcoma)

Leiomyosarcoma Rhabdomyosarcoma Malignant “triton” tumor

Atypical lipomatous tumor/

well-differentiated liposarcoma Dedifferentiated liposarcoma Myxoid/round cell liposarcoma Pleomorphic liposarcoma Bone and cartilaginous tumors Chondrosarcoma

Chordoma Extraskeletal mesenchymal chondrosarcoma

Myxoid chondrosarcoma Extraskeletal osteosarcoma Tumors of unknown etiology Malignant rhabdoid tumor

Synovial sarcoma Alveolar soft part sarcoma

Fig 5.2 Cystic lymphangiomas are composed of multiple, cystically

dilated lymphatics that often contain dense, lymphoid aggregates in

their walls The dilated empty spaces may contain occasional small

lymphocytes but are devoid of red blood cells

Fig 5.1 Gross appearance of cystic lymphangioma (cystic hygroma)

of the mediastinum in a child shows a smooth and shiny outer surface

distended by fl uid

5.1 Vascular Tumors

The majority of tumors originating from vascular

endothe-lium in the mediastinum are benign conditions that most

likely represent malformative or congenital processes

occur-ring duoccur-ring childhood or adolescence (Figs 5.1 , 5.2 , 5.3 , 5.4 ,

5.5 , 5.6 , 5.7 , 5.8 , 5.9 , 5.10 , 5.11 , 5.12 , 5.13 , 5.14 , 5.15 , 5.16 ,

5.17 , 5.18 , 5.19 , 5.20 , 5.21 , 5.22 , 5.23 , 5.24 , 5.25 , 5.26 , 5.27 ,

5.28 , 5.29 , 5.30 , 5.31 , 5.32 , 5.33 , 5.34 , 5.35 , 5.36 , 5.37 , 5.38 ,

5.39 , 5.40 , 5.41 , 5.42 , and 5.43 ) Benign, low-grade, and

malignant vascular neoplasms are extremely rare in the mediastinum and tend to occur more often in the pediatric population Paradoxically, one of the rarest forms of low- grade malignant vascular neoplasm, epithelioid hemangio- endothelioma (Figs 5.7 , 5.8 , 5.9 , 5.10 , 5.11 , 5.12 , 5.13 , 5.14 , 5.15 , 5.16 , 5.17 , 5.18 , 5.19 , 5.20 , 5.21 , 5.22 , 5.23 , 5.24 , 5.25 , 5.26 , 5.27 , 5.28 , 5.29 , 5.30 , 5.31 , 5.32 , 5.33 , 5.34 , 5.35 , 5.36 , and 5.37 ), represents the vascular malignancy most com- monly encountered in the mediastinum in adults

Fig 5.3 On higher magnifi cation, cystic lymphangiomas will disclose

small, rudimentary valves ( arrows ) in charge of regulating the lymph

fl ow

Fig 5.4 Mediastinal hemangiomas are most commonly of the

cavern-ous type and are characterized by multiple dilated vessels distended with red blood cells

5 Soft Tissue Tumors of the Mediastinum

Fig 5.5 At higher magnifi cation, the mediastinal hemangioma shows

thin-walled vessels lined by a single layer of endothelial cells and

con-taining red blood cells in their lumen

malformations that often contain other components admixed with the

vascular elements, such as smooth muscle, fat, and cartilage This

example shows a well-developed smooth muscle component

surround-ing the vessels, along with mature stromal fat

malignant vascular neoplasm of the mediastinum, where they are acterized by relatively low-grade malignant behavior and are associated with a very good survival rate following complete surgical excision The cut surface often shows a fl eshy, multinodular appearance with congestion and foci of hemorrhage Gritty foci of calcifi cations are also often noted

Fig 5.8 Histologically, epithelioid hemangioendothelioma is

charac-terized by a proliferation of large epithelioid cells with enlarged nuclei and abundant cytoplasm that can closely resemble an epithelial malig-nancy The nuclei show dispersed chromatin and prominent eosino-philic nucleoli; intranuclear cytoplasmic pseudoinclusions can be seen Despite the atypical appearance of the cells, mitoses are inconspicuous 5.1 Vascular Tumors

Fig 5.9 Epithelioid hemangioendothelioma vary greatly in growth

patterns and cytologic appearance The most common growth pattern is

a solid pattern composed of sheets of relatively monotonous epithelioid

tumor cells

Fig 5.10 A distinguishing and characteristic feature of epithelioid

hemangioendothelioma is the presence of multiple, scattered, single

cytoplasmic vacuoles associated with the tumor cells

Fig 5.11 On higher magnifi cation, the small cytoplasmic vacuoles are

seen to contain single red blood cells within their lumen It has been postulated that these cells may indicate an attempt by the tumor cells to create abortive vascular lumens

Fig 5.12 Another example of mediastinal epithelioid

hemangioendo-thelioma shows a sheet of large epithelioid cells dotted by numerous small, empty vacuoles that are quite conspicuous on scanning magnifi cation

5 Soft Tissue Tumors of the Mediastinum

epitheli-oid cells with small cytoplasmic vacuoles In some of the cells, the

vacuoles compress the nuclei to the periphery, creating a signet-ring

cell appearance

hemangioendothelioma of the mediastinum, including stromal

hyalin-ization and deposition of myxoid matrix This example shows an area

with extensive hyalinization and collagenization of the stroma

Fig 5.15 Another area from the same tumor shows prominent

depos-its of myxoid matrix that closely resemble the appearance of a nous matrix

Fig 5.16 Another unusual feature that is more commonly

encoun-tered in an epithelioid hemangioendothelioma in a mediastinal location

is the formation of metaplastic bone The bony spicules can be small and randomly scattered, or they can become quite prominent and easily identifi ed on chest imaging studies

5.1 Vascular Tumors

Fig 5.17 A somewhat related phenomenon observed in mediastinal

epithelioid hemangioendothelioma is the presence of clusters of

osteo-clastic, multinucleated giant cells in the stroma It has been postulated

that this phenomenon is related to focal hemorrhage and that the cells

appear as a result of chemotactic factors in response to the breakdown

of red blood cells

osteoclast- type multinucleated cells with numerous small nuclei The

cells are surrounded by abundant extravasated red blood cells

Fig 5.19 A less frequently encountered pattern of growth in

epitheli-oid hemangioendothelioma is characterized by anastomosing cords of tumor cells that are separated by abundant fi brous stroma, further enhancing the similarity to an epithelial malignant neoplasm

epithe-lioid tumor cells embedded in fi brous stroma, simulating a tic reaction by tumor

desmoplas-5 Soft Tissue Tumors of the Mediastinum

Fig 5.21 Another example of epithelioid hemangioendothelioma of

the mediastinum shows a pseudoinfi ltrative growth pattern composed of

short, irregular cords of large, epithelioid tumor cells

Fig 5.22 Higher magnifi cation shows irregular cords of epithelioid

cells, some of which appear to be forming imperfect or abortive lumens,

closely resembling a poorly differentiated carcinoma

Fig 5.23 The combination of abundant cytoplasmic vacuoles in the

tumor cells with a cord-like growth pattern can also enhance the larity with a metastatic carcinoma and raise the possibility of a signet- ring cell carcinoma Numerous scattered vacuoles containing nuclei that have been displaced to the periphery are seen in this fi eld

discrete cords of atypical tumor cells ( small arrows ) embedded in loose connective tissue A cell with a cytoplasmic vacuole ( large arrowhead )

closely simulates a signet-ring cell 5.1 Vascular Tumors

Fig 5.25 Another unusual appearance of epithelioid

hemangioendo-thelioma is caused by spindling of the tumor cells The spindling may

be a result of artifactual compression of tumor cells by stromal

overgrowth

Fig 5.26 Higher magnifi cation of epithelioid hemangioendothelioma

with spindling of tumor cells shows compressed, elongated nuclei with

tapered ends surrounded by abundant stromal collagen Such cases can

be confused with a variety of spindle-cell sarcomas

Fig 5.27 Another example of epithelioid hemangioendothelioma of

the mediastinum with a spindle-cell growth pattern This case shows a clearly fascicular pattern composed of spindle cells with focal storiform

pattern ( top left )

Fig 5.28 Higher magnifi cation of the example of epithelioid

heman-gioendothelioma in Fig 5.27 shows cells with elongated, matic nuclei surrounded by abundant eosinophilic cytoplasm

hyperchro-5 Soft Tissue Tumors of the Mediastinum

Fig 5.29 This example of epithelioid hemangioendothelioma of the

mediastinum shows a peculiar retiform pattern of growth, with

anasto-mosing trabeculae of tumor cells circumscribing islands of loose

con-nective tissue

trabeculae of tumor cells with abundant epithelioid cytoplasm,

resem-bling an epithelial malignancy

hemangioendothelioma is intravascular growth of tumor cells The tumor grows as polypoid or glomeruloid clusters of cells fi lling the lumen of dilated vessels

Fig 5.32 Higher magnifi cation of epithelioid hemangioendothelioma

of the mediastinum with intravascular tumor growth shows a small sel with the lumen fi lled by a polypoid collection of large epithelioid cells with abundant eosinophilic cytoplasm

ves-5.1 Vascular Tumors

Fig 5.33 Vessel-like growth pattern in an epithelioid

hemangioendo-thelioma of the mediastinum Large epithelioid tumor cells are seen

lining anastomosing vascular spaces containing scattered intraluminal

red blood cells There appears to be a continuous spectrum between

epithelioid hemangioendothelioma and epithelioid angiosarcoma; in

some cases, areas may be indistinguishable from epithelioid

angiosarcoma

with vessel-like spaces resulting in a striking hemangiopericytoma-like

pattern of growth Multiple small vessels with branching, patent lumens

are seen surrounded by the large epithelioid cells

Fig 5.35 Epithelioid hemangioendothelioma is easily diagnosed with

the use of immunohistochemical markers Stains for factor VIII, Ulex europaeus lectin, CD34, and CD31 will stain the tumor cells The image shows positivity of the tumor cells for CD31 in a case of medias-tinal epithelioid hemangioendothelioma

Fig 5.36 Unlike angiosarcomas, which show inconsistent positivity

for factor VIII (von Willebrand factor), epithelioid liomas are extremely sensitive for this stain Almost all show strong positivity for this antigen, as depicted in this image It is important to consider the possibility of epithelioid hemangioendothelioma in the diagnosis and include vascular markers in the panel of stains ordered, because many of these tumors may be also positive for cytokeratins; ordering only cytokeratin may lead to an incorrect diagnosis

hemangioendothe-5 Soft Tissue Tumors of the Mediastinum

Fig 5.37 Positivity for factor VIII-related antigen (von Willebrand

factor) is seen in this example of mediastinal epithelioid

hemangioen-dothelioma with a trabecular growth pattern The tumor closely

resem-bled a metastatic carcinoma on hematoxylin and eosin (H&E)-stained

sections, but positive staining for factor VIII and CD31 helped establish

the correct diagnosis

Fig 5.38 Angiosarcoma is a very rare tumor in the mediastinum The

tumors present as large, bulky, and hemorrhagic masses and may show

a spectrum that ranges from very well-differentiated tumors composed

of anastomosing vascular channels lined by atypical endothelial cells to

poorly differentiated lesions that can resemble other high-grade

sarco-mas The image shows an example of a well-differentiated

angiosar-coma showing well-developed vascular channels

anastomosing vascular channels lined by atypical endothelial cells secting through the stromal collagen

Fig 5.40 The epithelioid variant of angiosarcoma is characterized by

sheets of large epithelioid cells with marked cytologic atypia Notice the enlarged nuclei with prominent nucleoli and scattered mitotic fi g-ures Diagnosis of these tumors can be a challenge if angiosarcoma is not included in the differential diagnosis Use of appropriate immuno-histochemical stains can be of assistance in arriving at the correct diagnosis

5.1 Vascular Tumors

membranous and cytoplasmic positivity in the tumor cells of epithelioid

angiosarcoma of the mediastinum Borderline cases between

epitheli-oid hemangioendothelioma and epitheliepitheli-oid angiosarcoma can be

observed A novel molecular alteration—rearrangement of the CAMTA1

gene leading to the fusion of CAMTA1/WWTR1 —has been recently

identifi ed in high-grade epithelioid hemangioendothelioma but is not

present in epithelioid angiosarcoma Use of fl uorescence in situ

hybrid-ization (FISH) probes may be helpful in separating the two conditions

Fig 5.42 Angiosarcomas of the mediastinum can also be composed of

atypical spindle cells and can resemble other types of soft tissue

sarco-mas A search for more conventional areas demonstrating anastomosing

vascular channels will be helpful in the differential diagnosis

Fig 5.43 Higher magnifi cation of a mediastinal angiosarcoma with

spindle-cell morphology shows atypical spindle cells growing in cles with numerous mitotic fi gures The tumor cells were positive for CD31 and other vascular-associated markers, such as FLI1, WT1, and ERG

fasci-5 Soft Tissue Tumors of the Mediastinum

5.2 Fibroblastic and “Fibrohistiocytic”

Tumors

Tumors composed of fi broblastic cells represent the most

common type of mesenchymal neoplasms in the

mediasti-num (Figs 5.44 , 5.45 , 5.46 , 5.47 , 5.48 , 5.49 , 5.50 , 5.51 , 5.52 ,

5.53 , 5.54 , 5.55 , 5.56 , 5.57 , 5.58 , 5.59 , 5.60 , 5.61 , 5.62 , 5.63 ,

5.64 , 5.65 , 5.66 , 5.67 , 5.68 , 5.69 , 5.70 , 5.71 , 5.72 , 5.73 , 5.74 ,

5.75 , 5.76 , 5.77 , 5.78 , 5.79 , 5.80 , 5.81 , 5.82 , 5.83 , 5.84 , 5.85 ,

5.86 , 5.87 , and 5.88 ) Most are solitary fi brous tumors

(SFTs), a mesenchymal neoplasm that is composed of

den-dritic fi broblastic cells that show a peculiar CD34/bcl2+

immunophenotype and are believe to represent specialized

fi broblasts involved in antigen presentation in soft tissues

The vast majority of SFTs are benign; the malignant

counter-part of such tumors has been variously termed malignant

SFT or “dedifferentiated” SFT but could just as easily be

simply termed fi brosarcoma To establish a diagnosis of

malignant SFT, most authors would require demonstration of

a preexisting area of conventional SFT Cases in which areas

characteristic of conventional, benign SFT are not

demon-strable have been variously assigned to the category of ferentiated sarcomas, called “malignant fi brous histiocytoma”

undif-in the old literature

A number of immunohistochemical markers have been used in recent years to identify the better-differentiated tumors (SFTs), including CD34, bcl-2, and the recently developed STAT6 antibody, which identifi es a specifi c translocation that has been consistently demonstrated in these tumors The undifferentiated tumors, on the other hand, largely represent a diagnosis of exclusion; there are

no markers that permit assigning them to any specifi c gory It should be emphasized that the main differential diagnosis of malignant (and some benign) SFTs in the mediastinum includes dedifferentiated liposarcomas and monophasic synovial sarcomas The latter are easily distin- guishable from SFTs by their reactivity for cytokeratin and epithelial membrane antigen (EMA) and by the distinctive X;18 translocation; the former may be more diffi cult to dis- tinguish from SFTs because they can share STAT6 and CD34 positivity and will require identifi cation of areas of conventional liposarcoma and MDM2 positivity for differ- ential diagnosis

Fig 5.44 Solitary fi brous tumors (SFTs) are usually fl eshy and well-

circumscribed masses showing a lobulated, tan-white cut surface In the

mediastinum, however, the tumors more often appear to be invasive and

poorly circumscribed, and they tend to attain a larger size than their

pleural counterparts

Fig 5.45 SFTs are characterized by the striking variety of growth

pat-terns they can display The most common form is characterized by a bland-appearing, fi broblast-like spindle-cell proliferation with varying degrees of stromal collagenization On scanning magnifi cation, an SFT usually shows sharp circumscription from the surrounding tissues and

is composed of a dense spindle-cell population with vessels showing open lumens scattered throughout

5.2 Fibroblastic and “Fibrohistiocytic” Tumors

Fig 5.46 On higher magnifi cation, an SFT shows short fascicles of

spindle cells that may display a vaguely storiform pattern, sometimes

referred to as the “patternless” pattern

Fig 5.47 On higher magnifi cation, the cell population in an SFT is

quite monotonous and composed of small spindle cells with dispersed

chromatin, an absence of nucleoli, and an indistinct rim of amphophilic

cytoplasm Mitotic activity is very low to nil Most authors will accept

up to 3 mitoses per 10 high-power fi elds as the upper range acceptable

for a diagnosis of benign SFT

Fig 5.48 Immunohistochemical stains can be helpful to support the

diagnosis of SFT Most of the tumors will stain strongly positive for CD34 (40–70 %) and bcl-2 (80–100 %) (pictured) and will be negative for other differentiation markers such as cytokeratins, S-100 protein, actin, desmin, and epithelial membrane antigen (EMA)

Fig 5.49 The recently developed STAT6 antibody has been claimed to

be highly sensitive and specifi c for the diagnosis of SFT and shows nice nuclear positivity in most of the tumor cells A small proportion of low- grade, dedifferentiated liposarcomas can also react with this antibody, requiring caution for its interpretation

5 Soft Tissue Tumors of the Mediastinum

Fig 5.50 A constant theme observed in SFTs is stromal alterations,

particularly stromal sclerosis and hyalinization, which most often result

in a very striking picture characterized by parallel, ropelike strands of

hyalinized collagen that are fl anked by small spindle cells

hyalinized collagen showing a concentric arrangement around small

vessels and fl anked by fl attened, small spindle cells

Fig 5.52 Another unusual pattern of stromal collagenization in SFT is

characterized by focal deposits of dense collagen fi bers in a haphazard arrangement, although a perivascular arrangement around the lumen of small vessels is often apparent

cluster of irregularly deposited collagen fi brils adopting a somewhat stellate confi guration Structures such as these have been designated in the literature as “amianthoid” fi bers and are composed of abnormal collagen

5.2 Fibroblastic and “Fibrohistiocytic” Tumors

Fig 5.54 Another form of stromal alteration in SFT is characterized

by large, dilated vessels surrounded by a variously collagenized stroma,

resulting in an angiofi bromatous appearance Notice the inconspicuous

small spindle cells scattered within the surrounding stroma

Fig 5.55 Stromal changes in SFT may also include prominent

deposi-tion of myxoid matrix simulating stromal edema Such tumors can be

easily mistaken for a variety of myxoid soft tissue tumors; identifi cation

of more solid and conventional areas of SFT will be helpful for making

a correct diagnosis

Fig 5.56 SFTs often can be extremely cellular Such tumors are

char-acterized by a tightly packed proliferation of spindle cells with very little stroma, closely resembling monophasic synovial sarcoma or dedifferentiated liposarcoma

Fig 5.57 Higher magnifi cation of solid SFT showing compact sheets

of monotonous spindle cells circumscribing compressed vascular spaces These tumors can be virtually indistinguishable morphologi-cally from monophasic synovial sarcoma Positivity for CD34 and STAT6 would favor SFT, whereas synovial sarcomas should show focal positivity for cytokeratins and EMA

5 Soft Tissue Tumors of the Mediastinum

Fig 5.58 Another example of solid growth in SFT is characterized by

a striking herringbone pattern with fascicles of spindle cells that appear

to be branching from a central spine Monophasic synovial sarcoma and

MPNST can frequently display a similar growth pattern

Fig 5.59 Areas of hypercellularity in SFT frequently can alternate

with areas of hypocellularity In fact, this variegation in growth patterns

within the same tumor is quite distinctive for SFT and is a clue in

dis-tinguishing them from other spindle-cell soft tissue neoplasms

Fig 5.60 Another area in an SFT showing partial stromal

collageniza-tion adjacent to areas with stromal edema and loose fi brous tissue

Fig 5.61 Focal perivascular stromal collagenization is seen in this

SFT The spindle cells are very subtle and scant; the stroma shows extensive collagenization

5.2 Fibroblastic and “Fibrohistiocytic” Tumors

dilated vessels with open lumens surrounded by a population of spindle

cells with ropelike, linear arrays of collagen

Fig 5.63 Striking perivascular hyalinization is seen in this example of

SFT of the mediastinum The vessels are encased in a dense, cellular

spindle-cell proliferation The picture is reminiscent of a schwannoma

concentric layers of hyalinized collagen surrounding the walls of small vessels

Fig 5.65 Another distinctive feature of SFT is a vascular pattern

char-acterized by a hemangiopericytic proliferation of small vessels with branching and open lumens, simulating hemangiopericytoma It is now acknowledged that a signifi cant number of cases previously diagnosed

as hemangiopericytoma have corresponded to SFT with a striking hemangiopericytic pattern of growth

5 Soft Tissue Tumors of the Mediastinum