Ebook Thoracic imaging - Pulmonary and cardiovascular radiology (3/E): Part 2

(BQ) Part 2 book Thoracic imaging - Pulmonary and cardiovascular radiology has contents: The trachea, chronic obstructive pulmonary disease and emphysema, diffuse cystic lung diseases, the pleura and pleural disease,... and other contents.

Section Four

Airway Abnormalities

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CHAPTER 22

The Trachea

W RICHARD WEBB

THE NORMAL TRACHEA

The trachea extends from the inferior aspect of the cricoid cartilage (at the level of the sixthcervical vertebra) to the carina (at the level of the fifth thoracic vertebra) It measures from 10

to 12 cm in length The trachea is divided into extrathoracic and intrathoracic portions at thelevel it passes posterior to the manubrium; the extrathoracic trachea is 2 to 4 cm in length,while the intrathoracic trachea measures 6 to 9 cm in length From 16 to 22 horseshoe-shapedbands of hyaline cartilage support the anterior and lateral tracheal walls The incompleteposterior portion of these rings is bridged by a thin band of smooth muscle and fibrous tissue,

the posterior tracheal membrane (Fig 22.1)

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FIG 22.1 The normal trachea A: HRCT through the normal trachea The tracheal wall

(arrow) is outlined by mediastinal fat externally and usually is visible as a 1- to 2-mm soft

tissue stripe The posterior tracheal membrane usually appears thinner than the anterior andlateral tracheal walls and is variable in shape due to its lack of cartilage At this level, it is

partially obscured by the esophagus B: At the level of the aortic arch, the tracheal wall

(arrows) is outlined by mediastinal fat and the right lung in the region of the right

paratracheal stripe The tracheal wall appears thin C: Diagrammatic representation of the

normal components of the tracheal wall

The plain film appearance of the trachea is described in Chapter 2 On CT, the tracheausually is round or oval in shape, but it can appear horseshoe shaped, triangular, or like aninverted pear in some normal patients The tracheal wall is delineated by air in its lumeninternally and by mediastinal fat externally and is usually visible as a 1- to 2-mm soft tissuestripe The posterior tracheal membrane appears thinner than the anterior and lateral trachealwalls and is variable in shape due to its lack of cartilage; it can appear convex, concave, orflat The tracheal cartilages may appear calcified or slightly denser than adjacent soft tissue.Calcification of cartilage is most common in older patients and is particularly common inwomen (Fig 22.2) In patients with calcified cartilage, little soft tissue is seen in the trachealwall internal to the cartilage

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FIG 22.2 Normal calcification of tracheal cartilage in an elderly woman Discontinuous

calcification of the tracheal wall reflects calcification of individual cartilage rings Thetracheal wall appears thin

Tracheal diameter varies widely in normal subjects In normal men, tracheal diameteraverages 19.5 mm, with a range of 13 to 25 mm (mean ± 3 SD) in the coronal plane and 13 to

27 mm in the sagittal plane In women, tracheal diameter is slightly smaller, averaging 17.5

mm and ranging from 10 to 21 mm in the coronal plane and 10 to 23 mm in the sagittal plane

On CT performed during or after forced expiration, the posterior tracheal membranebulges anteriorly, narrowing and, in some cases, nearly obliterating the tracheal lumen (Fig.22.3) The mean anterior-posterior diameter of the trachea decreases by 30% to 40% during

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forced expiration due to anterior bulging of the posterior membrane; the transverse diameterdecreases by 10% to 20% The cross-sectional area of the trachea may diminish by more than50% in normal subjects with forced expiration.

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FIG 22.3 Normal expiratory CT A: On inspiration, the trachea has a rounded appearance B: During a dynamic forced expiratory scan, there is marked anterior bowing of the posterior

tracheal membrane (arrow) This appearance is normal Little side-to-side narrowing occurs

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because of the tracheal cartilage.

Tracheal Bronchus

A tracheal bronchus represents the origin of all or part (usually the apical segment) of theright upper lobe bronchus from the trachea; its incidence is about 0.1% (see Figs 8.1 and 8.2

in Chapter 8) Left tracheal bronchus also occurs but is much less common

TRACHEAL NARROWING

Focal tracheal narrowing may be seen with tracheal tumors (Table 22.1), tracheomalacia(TM), tracheal stenosis or stricture, saber-sheath trachea, granulomatosis with polyangiitis(GPA), amyloidosis, sarcoidosis, or tuberculosis (TB) or other infections (Table 22.2)

Diffuse or generalized tracheal narrowing may be seen with TM, saber-sheath trachea,GPA, amyloidosis, tracheobronchopathia osteochondroplastica, relapsing polychondritis,sarcoidosis, and some infections

Stenting is sometimes used to treat TM, tracheal stenosis, polychondritis, and GPA.Surgery may be employed for localized or focal lesions

Tracheal Tumors

Tumors of the trachea are rare (Table 22.1) Symptoms often are absent or nonspecific (e.g.,cough, dyspnea), and early diagnosis is difficult Tracheal tumors tend to be inconspicuous onchest radiographs and may become quite large before they are detected CT is highlysensitive in detecting tracheal tumors and their extent of spread Together, squamous cellcarcinoma and adenoid cystic carcinoma account for more than 85% of tracheal tumors.Tumors of many other cell types, both epithelial and mesenchymal, may occur in the tracheabut are much less common Ten percent of tracheal tumors are benign

TABLE 22.1 Tracheal Tumors

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Squamous cell carcinoma is most common (45% to 65% of cases) It is associated with

smoking and is multifocal in 10% of cases, often involving the distal trachea; a mainbronchus also may be involved (see Figs 4.37 and 4.38 in Chapter 4) Adenoid cystic

carcinoma originates from tracheal mucous glands and is most common in the upper trachea

(Figs 22.4 and 22.5) It is less common than squamous cell carcinoma Adenoid cysticcarcinoma often arises from the posterolateral tracheal wall (Figs 22.5 and 22.6B)

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FIG 22.4 Adenoid cystic carcinoma of the proximal trachea An eccentric narrowing

(arrows) of the tracheal lumen is caused by a sessile mass arising from the right tracheal wall.

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FIG 22.5 Adenoid cystic carcinoma of the trachea A: A large mass (large arrows) in the

upper trachea markedly narrows the tracheal lumen (small arrow) and invades the

mediastinum B: On a sagittal reconstruction, the mass (arrows) can be seen to arise from the

posterior tracheal wall This location is typical of adenoid cystic carcinoma

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FIG 22.6 CT appearances of primary tracheal tumor A: Tracheal malignancies may appear polypoid, sessile, or circumferential B: Adenoid cystic carcinoma results in a sessile mass

(M) arising from the posterior tracheal wall and protruding into the tracheal lumen The mass extends into the adjacent mediastinum (arrows).

On CT, a primary malignant tracheal tumor may appear as a polypoid lesion, a focalsessile lesion, eccentric narrowing of the tracheal lumen, or circumferential wall thickening(see Fig 22.5) Attachment to the tracheal wall may be either broad based (Fig 22.5) ornarrow and pedunculated CT may underestimate the longitudinal extent of the tumor;submucosal spread may be difficult to see on CT However, CT is superior to bronchoscopy

in evaluating extraluminal spread and the trachea distal to an obstructing lesion

Metastases to the trachea may occur via direct extension or by hematogenous spread.

Direct extension to involve the trachea most often is secondary to a primary tumor of thelung, larynx, esophagus, or thyroid These tumors may compress the trachea, displacingtracheal cartilage inward, or may invade the tracheal lumen, with tumor being seen asabnormal tissue internal to tracheal cartilage (Fig 22.7; also see Fig 4.56 in Chapter 4)

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Hematogenous metastases usually originate from melanoma or from carcinomas of the breast,colon, or kidney On CT, hematogenous metastases may appear as single or multiple, sessile,

or pedunculated endotracheal lesions (Fig 22.8)

FIG 22.7 Esophageal carcinoma with tracheal invasion Tumor has invaded the trachea and

is seen as soft tissue (small arrows) internal to the calcified tracheal cartilage (large arrows).

The tracheal lumen is narrowed

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FIG 22.8 Tracheal metastasis Tracheal metastases may result in tracheal compression with

inward displacement of the tracheal wall, an endotracheal mass, or a combination of these

findings A, B: There is narrowing of the trachea with an endoluminal mass (arrow) C: Soft

tissue window at the same level as (B) shows a mass involving the right tracheal wall and

mediastinal soft tissues (arrows).

Squamous cell papilloma is the most common benign tracheal tumor It represents an

abnormal proliferation of squamous epithelium and may appear sessile, papillary, lobulated,

or polypoid Solitary papilloma is associated with smoking and is most common in adults.The condition of multiple papillomas (i.e., papillomatosis) usually begins in childhood withlaryngeal involvement and is associated with human papillomavirus infection On CT, asolitary papilloma appears as a well-circumscribed nodule that is confined to the tracheal walland projects into the tracheal lumen; it often shows acute angles where it contacts the trachealwall Tracheal cartilage is unaffected Papillomatosis is characterized by numerous nodulesinvolving the entire length of the trachea (see Fig 4.25 in Chapter 4) or diffuse thickening of

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the tracheal wall (Fig 22.9) Other benign tracheal tumors include hamartoma and tumors ofmesenchymal origin such as lipoma or chondroma.

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FIG 22.9 Tracheobronchial papillomatosis with tracheal wall thickening A: Concentric

thickening of the tracheal wall (arrows) is due to diffuse involvement by papillomas The

tracheal lumen is markedly narrowed B: Multiple cystic pulmonary lesions may be seen in

some patients with tracheobronchial papillomatosis

Tracheomalacia

TM refers to weakness of the tracheal wall, usually due to abnormalities of the tracheal

cartilage, associated with excessive collapsibility of the trachea on expiration (Table 22.2)

The term tracheobronchomalacia (TBM) is used in bronchi that are also abnormally

collapsible TM may be congenital and associated with deficient cartilage, but most often isacquired as a result of intubation injuries, tracheal compression by extrinsic masses orvascular lesions (e.g., aortic aneurysm), chronic infection, or chronic obstructive pulmonarydisease or in association with saber-sheath trachea, relapsing polychondritis, ortracheobronchomegaly It may be localized, or it may involve a long tracheal segment Adistinction is sometimes made between TM, in which tracheal cartilage weakness is

responsible for collapse, and excessive dynamic airway collapse (EDAC), in which there is

excessive invagination of the posterior tracheal membrane with expiration TM and EDACmay coexist

TABLE 22.2 Nonneoplastic Tracheal Diseases

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Abnormal flaccidity of the tracheal wall may result in inefficient cough, retention ofsecretions, and chronic airway infection and bronchiectasis Symptoms include recurrentinfection, dyspnea, and stridor.

Radiographs or CT on inspiration may show increased or decreased tracheal diameter inpatients with TM The hallmark of TM is a significant decrease in the tracheal diameter orcollapse of the tracheal walls with expiration (Fig 22.10) Tracheal collapse may be diffuse,side to side, or less often anterior to posterior A 50% decrease in tracheal diameter or cross-sectional area with expiration has been considered indicative of TM, but this degree oftracheal narrowing may be seen in up to 75% of normal, particularly associated withinvagination of the posterior membrane

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FIG 22.10 Tracheomalacia in a patient with pulmonary function test findings of airway

obstruction and “negative effort dependence” (the harder the patient tried to expire, the more

obstruction there was) A: CT obtained on inspiration shows the trachea to be normal in caliber There is a mild saber-sheath tracheal deformity (B) Following a forced expiration,

there in marked narrowing of the lumen of the trachea with reduction in both its coronal andits sagittal diameters

With forced expiration, invagination of the posterior tracheal membrane may result innear-complete obliteration of the tracheal lumen in some normal subjects (see Fig 22.3).Side-to-side reduction of tracheal diameter with expiration is more typical of symptomatic

TM A diagnosis of TM should generally be avoided in the absence of symptoms orpulmonary function findings of airway obstruction (Fig 22.10) Tracheal stents may be used

following extubation typically is present Inflammation and pressure necrosis of the trachealmucosa most commonly occur at either the tracheostomy stoma or at the level of the tubeballoon, 1 to 1.5 cm proximal to the tube tip; the stenosis usually involves 1.5 to 2.5 cm ofthe tracheal wall The extrathoracic trachea most often is involved Focal narrowing may beseen if the tube tip presses on one part of the tracheal wall, usually the anterior wall.

Acute postintubation stenosis results from edema of the tracheal wall or intraluminal

granulation tissue Plain films may show an eccentric or hourglass-shaped trachealnarrowing On CT, this may be seen as eccentric or concentric soft tissue internal to normal-appearing tracheal cartilage (Fig 22.11) The outer tracheal wall has a normal appearance,without evidence of deformity or narrowing Dynamic expiratory images show little change

in tracheal dimensions

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FIG 22.11 Postintubation tracheal stenosis due to granulation tissue A: Near the thoracic inlet, the trachea appears normal B: Below the level shown in (A), focal narrowing of the

tracheal lumen is associated with increased soft tissue (white arrows) within the tracheal lumen The calcified tracheal cartilage (black arrows) appears normal, without evidence of

deformity or collapse C: Coronal reconstruction in a patient with an hourglass-shaped

tracheal stenosis following intubation The tracheal wall appears normal (large arrows), and

granulation tissue is seen narrowing the tracheal lumen (small arrows) D: Diagrammatic

representation of tracheal stenosis due to granulation tissue, compared to the appearance of a

normal trachea (From Webb EM, Elicker BM, Webb WR Using CT to diagnose

nonneoplastic tracheal abnormalities: appearance of the tracheal wall AJR Am J Roentgenol

2000; 174:1315–1321.)

With chronic postintubation stenosis or stricture, fibrosis usually is present with

deformity of tracheal cartilage and collapse of the tracheal wall On CT, thickening of themucosa and submucosa is absent or mild, and deformity of the tracheal cartilage or posteriortracheal membrane accounts for narrowing of the lumen (Figs 22.12 and 22.13) The area ofnarrowing may be thin and weblike or long and hourglass shaped Dynamic expiratoryimages may or may not show significant malacia Because of the focal nature of the stenosis,treatment with stenting is useful

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FIG 22.12 Postintubation tracheal stenosis due to stricture A, B: CT at two levels shows

side-to-side narrowing of the tracheal lumen resulting from deformity of the tracheal cartilage

(arrows) C: Diagrammatic representation of tracheal stenosis due to cartilage deformity,

compared to the appearance of a normal trachea (From Webb EM, Elicker BM, Webb WR.

Using CT to diagnose nonneoplastic tracheal abnormalities: appearance of the tracheal wall

AJR Am J Roentgenol 2000; 174:1315–1321.)

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FIG 22.13 Postintubation tracheal stenosis due to deformity of tracheal cartilage A: CT

shows side-to-side narrowing of the tracheal lumen resulting from deformity of the tracheal

cartilage (arrows) The tracheal wall is outlined by mediastinal fat B: Coronal reconstruction

shows an hourglass-shaped stenosis, with inward collapse of the tracheal wall (white arrows).

Calcified tracheal cartilage (black arrow) is displaced inward C: Three-dimensional

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reconstruction shows the hourglass-shaped stenosis (arrows).

Acute and chronic tracheal or bronchial stenosis may also result from sarcoidosis,histoplasmosis or other fungi, GPA, and inflammatory bowel disease

Saber-Sheath Trachea

Saber-sheath trachea is common and almost always is associated with chronic obstructivepulmonary disease It is characterized by a marked decrease in the coronal diameter of theintrathoracic trachea associated with an increase in its sagittal diameter (Fig 22.14); theextrathoracic trachea is normal Although it may involve the entire intrathoracic trachea, in itsearliest stages, it is visible only at the thoracic inlet It is thought to be due to chronic injuryand malacia of tracheal cartilage due to coughing or increased intrathoracic pressure Themain bronchi are of normal size

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FIG 22.14 Saber-sheath trachea in a patient with chronic obstructive pulmonary disease A:

PA chest radiograph shows hourglass-shaped narrowing of the intrathoracic trachea (black

arrows) The extrathoracic trachea (white arrows) appears normal B: In the lateral

projection, the tracheal diameter appears normal or increased (arrows).

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On frontal radiographs, a characteristic side-to-side narrowing of the tracheal lumen isvisible beginning at the thoracic inlet (see Fig 22.14) The right paratracheal stripe, primarilyrepresenting tracheal wall, appears normal or slightly increased in thickness On the lateralradiograph, the tracheal diameter appears normal or slightly increased If the trachealdiameter on the lateral film measures 1.5 times that seen on the frontal film, saber-sheathtrachea is considered to be present.

On CT, there is inward displacement of the lateral portions of the tracheal wall andtracheal cartilage with side-to-side narrowing of the tracheal lumen (Fig 22.15) The trachealwall usually is of normal thickness During forced expiration, CT demonstrates furtherinward bowing of the tracheal walls in many patients

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