Congenital Bronchopulmonary Lesions

W. Richard Webb

A variety of congenital abnormalities may involve the bronchi, lung and it vascular supply. They often have characteristic plain film and computed tomography (CT) findings. Congenital abnormalities of the aorta and great vessels are reviewed in Chapter 35.

BRONCHIAL ANOMALIES

Anomalies of bronchial anatomy include abnormal origin, absent branches, supernumerary branches, and congenital diverticula (Table 1-1). Minor variation in subsegmental bronchial anatomy is common but clinically insignificant; a detailed knowledge of subsegmental bronchial anatomy is not necessary for clinical practice. Variation in segmental bronchial anatomy is less frequent and not often of significance.

Tracheal Bronchus

A tracheal bronchus is present in about 0.1% of the population. It usually arises from the right tracheal wall, at or within 2 cm of the tracheal bifurcation. It supplies a variable portion of the medial or apical right upper lobe, most often the apical segment (Fig. 1-1); in occasional cases, the entire right upper lobe bronchus arises from the trachea (Fig. 1-2). When a right-sided tracheal bronchus is present, the azygos arch is seen above the tracheal bronchus. Tracheal bronchus is sometimes referred to as a “pig bronchus” or “bronchus suis” as it is common in pigs and other clovenhoofed animals.

In most cases, this anomaly is insignificant. However, recurrent infection or bronchiectasis may result, since the tracheal bronchus is often slightly narrowed at its origin. A left tracheal bronchus, supplying the apical posterior segment of the left upper lobe, is rarely present; it is much less common than a right-sided tracheal bronchus. The term “tracheal bronchus” is sometimes used to refer to a displaced bronchus, supplying a part of the upper lobe, even if it does not arise from the trachea.

Accessory Cardiac Bronchus

Accessory cardiac bronchus is a supernumerary bronchus with an incidence of about 0.1%. It arises from the medial wall of the bronchus intermedius or right lower lobe bronchus and extends inferiorly and medially toward the mediastinum or heart. In some cases, the cardiac bronchus is a short, blind-ending bronchial stump without associated alveolar tissue, and it may terminate in the mediastinum. In others, a longer branching bronchus is present, associated with rudimentary lung tissue (Fig. 1-3). In most cases, this anomaly is an incidental finding; occasionally, chronic infection or hemoptysis is associated.

Bronchial Isomerism

Bronchial isomerism refers to bilateral symmetry of the bronchi and associated pulmonary lobes. It may be isolated or associated with a variety of anomalies, particularly congenital heart disease. Bronchial anatomy may be bilaterally right sided (associated with asplenia) or left sided (associated with polysplenia).

TABLE 1.1 Bronchial Anomalies

Variations in subsegmental branching
	Common but insignificant
Tracheal bronchus
	Incidence 0.1%
	Arises from right tracheal wall; rare on left
	Usually supplies apical segment of right upper lobe
	Rarely supplies entire right upper lobe
	Increased incidence of infection or bronchiectasis
Accessory cardiac bronchus
	Incidence 0.1%
	Arises from medial wall of bronchus intermedius
	Usually blind ending or supplies rudimentary lung
	May terminate in the mediastinum
	Increased incidence of infection or hemoptysis
Bronchial isomerism
	Symmetrical bronchial anatomy
	Bilateral right- or left-sided bronchial anatomy
	Associated with congenital heart disease, other anomalies

FIG. 1.1. Tracheal bronchus. A: Coronal CT reconstruction shows a tracheal bronchus (Tr Br) arising from the right tracheal wall just above the carina. The azygos arch (Azygos) is visible above the bronchus. B: CT (1.25-mm slice thickness) shows the origin of the tracheal bronchus. As in this case, slight narrowing at the origin of the bronchus is common. The bronchus supplies the apical segment of the right upper lobe. C: The tracheal carina is seen slightly below (B). D: Below (C), the main right upper lobe bronchus (RUL) gives rise to the anterior (Ant Seg) and posterior (Post Seg) segmental bronchi.

BRONCHIAL ATRESIA

Bronchial atresia is a developmental defect characterized by local narrowing or obliteration of a lobar, segmental, or subsegmental bronchus (Table 1-2). It is most common in the left upper lobe, followed by the right upper and right middle lobes; it is less common in the lower lobes. This entity is usually detected incidentally in adults and is undoubtedly related to congenital lobar emphysema (CLE). Patients usually have no symptoms, but lung distal to the obstruction may occasionally become infected. In patients with chronic infection, resection may be necessary.

The lobe or segment distal to the bronchial obstruction usually remains aerated because of collateral ventilation

(Figs. 1-4 and 1-5). In 90% of cases, air trapping in the distal lung results in decreased perfusion; radiographs and CT show the affected lung to be hyperlucent and hypovascular. Affected lung is often increased in volume, resulting in mediastinal shift or shift of a fissure. In 80% of cases, mucus accumulates within dilated bronchi distal to the obstruction, resulting in a tubular, branching, or ovoid density (mucous plug or mucocele). Mucus within dilated bronchi usually appears low in attenuation. Expiratory radiographs or CT scans show air trapping (see Fig. 1-5B).

FIG. 1.2. Tracheal bronchus in a patient with pneumonia. A: Coronal reconstruction shows the entire right upper lobe bronchus (RUL) arising from the right tracheal wall above the carina. The apical segmental bronchus extends superiorly. B: Transaxial CT shows the right upper lobe bronchus (arrow) giving rise to anterior and posterior segments. Patchy areas of increased lung opacity reflect the presence of pneumonia.

FIG. 1.3. Accessory cardiac bronchus. A: Coronal CT reconstruction shows an accessory cardiac bronchus (CB) arising from the medial aspect of the bronchus intermedius (BI), to supply a small region of lung. B: Transaxial image shows the cardiac bronchus (CB) arising from the medial wall of the bronchus intermedius (BI). (Figure continues.)

FIG. 1.3. (Continued.) C: Slightly below (B), the cardiac bronchus (arrow) is seen medial to the bronchus intermedius. D: Below (C), the bronchus supplies a small segment of lung separated from the lower lobe by an accessory fissure (arrows).

TABLE 1.2 Bronchial Atresia

Narrowing or obliteration of a lobar, segmental, or subsegmental bronchus
Left upper lobe > right upper lobe > right middle lobe > lower lobes
Detected incidentally in adults
Infection may occur
Mucous plug distal to obstructed bronchial segment
Distal lung
	Lucent
	Increased in volume
	Decreased vessel size
	Air trapping on expiration
Rule out obstructing tumor

The combination of these typical radiographic or CT findings in a young patient is strongly suggestive of the diagnosis. Bronchoscopy may be warranted to rule out another cause of bronchial obstruction, such as tumor.

CONGENITAL LOBAR EMPHYSEMA

CLE, also known as congenital lobar hyperinflation, is characterized by marked overinflation of a lobe (Table 1-3). Most cases present within the first month of life; symptoms of respiratory distress are typical. Presentation after the first month may occur.

Most cases of CLE are associated with partial or complete bronchial obstruction occurring as a result of (a) deficient cartilage; (b) external compression, usually by an anomalous vessel or bronchogenic cyst; or (c) luminal abnormalities such as mucosal folds. Some cases are unassociated with bronchial obstruction.

CLE is most common in the left upper lobe, followed by the right middle lobe and right upper lobe. Only a few percent
occur in the lower lobes. Radiographs typically show marked overinflation and air trapping in the affected lobe. However, in neonates, the affected lobe may sometimes appear opaque because of retained fetal lung fluid. Mediastinal shift away from the abnormal lobe often occurs, and normal lobes are reduced in volume. Resection is often necessary.

FIG. 1.4. Bronchial atresia. A: Chest radiograph in a young patient with bronchial atresia involving the left upper lobe. The left upper lobe is increased in volume, with mediastinal shift toward the right side. The lobe is lucent, and its vascularity is decreased. B: Transaxial CT shows the left upper lobe to be increased in volume, with mediastinal shift to the right, hyperlucent, and hypovascular. Branches of the left upper lobe bronchus are dilated, and one branch contains a mucous plug (arrows). C: Coronal reconstruction shows the hyperlucent and hypovascular left upper lobe with focal atresia of its apical-posterior segmental branch (arrow). Distal bronchi are dilated.

It is reasonable to assume that cases of CLE that go unrecognized at birth may be diagnosed years later as bronchial atresia.

FIG. 1.5. Bronchial atresia. A: CT shows a branching mucous plug (white arrow) in the location of the posterior segmental bronchus of the right upper lobe. Lung distal to the bronchus (black arrows) is hyperlucent and hypovascular. Mediastinal shift to the left side is present. B: Expiratory CT shows air trapping in the lung distal to the obstructed bronchus. Normal lung increases significantly in attenuation relative to (A).

PULMONARY BRONCHOGENIC CYST

Bronchogenic cysts are foregut duplication cysts and result from abnormal development of the lung bud. They are lined by pseudostratified ciliated columnar epithelium, typical of bronchi. The cyst wall may also contain smooth muscle, mucous glands, or cartilage. Bronchogenic cysts are filled with fluid, which can be serous, hemorrhagic, or highly viscous and gelatinous because of its high protein content.

Bronchogenic cysts may be mediastinal or pulmonary. Mediastinal bronchogenic cysts are much more common than pulmonary cysts. They are discussed along with mediastinal masses in Chapter 8.

Pulmonary bronchogenic cysts are most common in the medial lung and the lower lobes (Table 1-4). They are sharply circumscribed and round or oval. The cyst wall may calcify. Rarely, the cyst may contain milk of calcium and appear dense. Cysts may slowly increase in size; a rapid increase in size is unusual unless infection occurs.

TABLE 1.3 Congenital Lobar Emphysema

Partial or complete bronchial obstruction caused by:
	Deficient cartilage
	External compression
	Luminal abnormalities
Some cases unassociated with bronchial obstruction
Left upper lobe > right middle lobe > right upper lobe > lower lobes
Respiratory distress in neonates
Presentation after first month uncommon
Marked overinflation of lobe
Air trapping
Sometimes the abnormal lobe retains fetal lung fluid
Resection often necessary

About half of fluid-filled bronchogenic cysts appear to be low in attenuation on CT (0 to 20 HU) (Fig. 1-6). However, as with mediastinal bronchogenic cysts, the CT attenuation of a pulmonary bronchogenic cyst is variable. High CT numbers (40 to 80 HU), suggesting a solid mass, can be seen. Such cysts contain bloody or thick, proteinaceous fluid. Typically, the cyst wall appears very thin on CT or is invisible. A bronchogenic cyst may sometimes appear to be related to a small bronchus.

Infection eventually occurs in 75% of cases. In the presence of acute infection, a rapid increase in size of the cyst may be seen. Also, the outer cyst wall may become less well defined because of surrounding lung inflammation. During or after infection, a cyst may contain air (Fig. 1-7; see also Fig. 9-29 in Chapter 9) or a combination of air and fluid (with an air-fluid level). When the cyst contains air, its wall appears very thin.

TABLE 1.4 Pulmonary Bronchogenic Cyst

Foregut duplication cyst
Lined by bronchial epithelium
Fluid contents can be serous, hemorrhagic, or viscous
Less common than mediastinal bronchogenic cyst
Most common in medial lung and lower lobes
Sharply circumscribed and round or oval
Thin wall; occasionally calcifies
Contents 0-20 HU in half; often 40-80 HU; milk of calcium rare
Infection occurs in 75%

	Rapid increase in size
	Blurring of outer edge
	Air-fluid level
	Air in cyst may remain after infection

FIG. 1.6. Pulmonary bronchogenic cyst. A sharply marginated round nodular opacity (arrow) is visible in the right lower lobe. This measured 0 HU in attenuation. This appearance is typical of a fluid-filled bronchogenic cyst.

CONGENITAL CYSTIC ADENOMATOID MALFORMATION (CONGENITAL PULMONARY AIRWAY MALFORMATION)

Congenital cystic adenomatoid malformation (CCAM), also termed congenital pulmonary airway malformation (CPAM) consists of a multicystic, intralobar mass of disorganized lung tissue, derived primarily from bronchioles. About 70% present during the first week of life, but 10% are diagnosed after the first year, and rare cases in adults have been reported.

CCAM/CPAM can involve an entire lobe. Lower lobes are most often involved, but any lobe can be affected. The CCAM/CPAM communicates with the bronchial tree and is supplied by the pulmonary artery; systemic arterial supply is rarely present.

FIG. 1.7. Pulmonary bronchogenic cyst. A thin-walled, sharply marginated, air-filled bronchogenic cyst is visible in the left lung. The presence of air within the cyst indicates prior infection.

TABLE 1.5 Congenital Cystic Adenomatoid Malformation (CCAM)

Also known as Congenital Pulmonary Airway
	Malformation (CPAM)
Multicystic, intralobar mass of disorganized lung tissue
70% present in first week; 10% after first year
Respiratory distress in neonates; recurrent infection in adults
Most common in lower lobe
Three primary types
Type 1 (65%)
	One or more cysts, >2 cm in diameter
	May appear initially as solid mass
	Large air-filled multicystic lesion
	Sometimes with air fluid levels
	May occupy the entire hemithorax
Type 2 (20%-25%)
	Multiple cysts >2 cm in diameter
	May appear initially as solid mass
	Air-filled multicystic mass or focal consolidation
	Associated renal and cardiac abnormalities
	Often a poor prognosis
Type 3 (10%)
	Microscopic (<3-5 mm) cysts
	Appears as solid mass
Two additional types proposed, based on histology, each a few percent of cases
Type 0
	Small cysts
	Similar to Type 3 in appearance
Type 4
	Large cysts
	Similar to Types 1 and 2 in appearance

CCAMs are typically classified into three primary types (Types 1 to 3), which have different histology, gross pathologic findings, radiographic appearance, and prognosis (Table 1-5).

Type 1 CCAMs (65% of cases) contain one or more cysts more than 2 cm in diameter (Fig. 1-8). They usually appear radiographically as a large, air-filled multicystic lesion, sometimes with air-fluid levels, which may occupy the entire hemithorax.

Type 2 CCAMs (20% to 25% of cases) contain multiple cysts less than 2 cm in diameter. They present radiographically as an air-filled multicystic mass or a solid mass or area of consolidation (see Fig. 1-9). This type may be associated with a poor prognosis because of associated renal and cardiac abnormalities.

Type 3 CCAMs (10% of cases) contain microscopic (less than 3 to 5 mm) cysts and present radiographically as a solid mass.

Two additional types of CCAM have been proposed, Types 0 and 4, based on histopathologic findings and the type of airway epithelium involved in the malformation. The term CPAM (congenital pulmonary airway malformation) has been suggested to encompass this expanded classification. Types 0 and 4 CCAM/CPAM each account for a few percent of cases. Type 0 CCAM/CPAM is associated with small cysts,
as in Type 3. Type 4 CCAM/CPAM is associated with large cysts, as is Type 1; its radiographic and CT appearance is the same as for Type 1 or 2.

FIG. 1.8. Type 1 congenital cystic adenomatoid malformation. A multicystic lesion is visible in the right lower lobe. This is a typical appearance of Type 1 CCAM in an adult.

Sonography can be used for prenatal diagnosis. Findings include polyhydramnios, fetal hydrops, and a solid or cystic mass in the fetal thorax. Fetal surgery may be attempted.

In infancy, CCAM/CPAM presents as a space-occupying lesion. Symptoms of respiratory distress are common. In neonates, CCAM/CPAM usually presents as a solid mass regardless of its type. Types 1 and 2 may become air filled over a period of days to weeks. They are often associated with progressive air trapping and mediastinal shift to the opposite side.

The treatment of choice is excision of the affected lobe. The prognosis of neonates with CCAM/CPAM is adversely affected by large size, underdevelopment of uninvolved lung (i.e., the presence of associated lung hypoplasia), and the presence of associated fetal hydrops or other congenital anomalies.

In adults, CCAM/CPAM usually presents as an air-filled or air- and fluid-filled cystic or multicystic mass. Most adults present with recurrent pneumonia, although recurrent pneumothorax has also been associated. Occasionally, bronchioloalveolar carcinoma may arise in relation to a CCAM/CPAM.

PULMONARY ARTERIOVENOUS MALFORMATION

Congenital arteriovenous malformation (AVM), also known as arteriovenous fistula, likely results from deficient formation or abnormal dilation of pulmonary capillaries due to a developmental defect in the capillary wall. From 35% to 67% of cases are associated with Osler-Weber-Rendu syndrome (hereditary hemorrhagic telangiectasia), in which AVMs are found in the skin, mucous membranes, and viscera (Table 1-6). Also, AVMs may rarely occur in patients with hepatopulmonary syndrome or as a result of trauma.

FIG. 1.9. Type II congenital cystic adenomatoid malformation. A solid mass (black arrow) is visible in the right lower lobe of a neonate. An opacified vessel is visible within the mass (white arrow). Type II CCAM may present as an air-filled or fluid-filled mass.

Pulmonary arteriovenous fistulas slowly enlarge over time and are usually first diagnosed in adulthood. More than two thirds of AVMs are found in the lower lobes, and they are typically subpleural in location. Fistulas are multiple in 35% of patients and bilateral in 10%.

Simple and Complex Arteriovenous Malformations

A simple AVM is a single, dilated vascular sac connecting one artery and one vein (Figs. 1-10 and 1-11). It is

most frequent and accounts for the bulk of cases of AVM. Complex AVMs, which have more than one feeding artery, are rare.

TABLE 1.6 Pulmonary Arteriovenous Malformation (AVM)