Congenital lobar emphysema (CLE) is a disorder affecting neonates and young infants and is usually associated with acute or subacute respiratory distress. It may occasionally present as an incidental finding in adults. Various bronchial and alveolar abnormalities can cause this disorder, and in some cases the cause is unknown. The most commonly detected abnormality is absence or hypoplasia of cartilage rings of major and branch bronchi, with resultant bronchial collapse during exhalation. This results in inhalational air entry but collapse of the narrow bronchial lumen during exhalation. The bronchial obstruction leads to progressive hyperinflation and air trapping (Fig. 16-1), usually involving only one pulmonary lobe. The left upper lobe is most commonly involved, followed by the right middle and right upper lobes. CLE has two forms: hypoalveolar (fewer than expected number of alveoli) and polyalveolar (greater than expected number of alveoli). The pulmonary vasculature, although frequently attenuated, is usually normal in structure and distribution. Common chest radiographic findings include a hyperlucent lobe, compressive atelectasis of adjacent parenchyma, and contralateral mediastinal shift (1). In some cases, a subtle hyperlucent lobe may be all that is seen. Computed tomography (CT) best characterizes this abnormality and typically shows a hyperlucent, hyperexpanded lobe;
attenuated but intact pattern of vascularity; compression of the adjacent lung; and contralateral mediastinal shift.

Bronchogenic cysts result from abnormal growth of the lung bud and can be either mediastinal or intrapulmonary. Both types are lined with ciliated columnar epithelium and contain serous or mucous material. No clear-cut predilection for an intrapulmonary or a mediastinal location has been demonstrated. An intrapulmonary bronchogenic cyst often communicates with the bronchial tree, which can result in air–fluid levels and recurrent infections that may damage the cyst wall. Chest radiographs show a nonspecific oval or round, well-circumscribed mass, often as an incidental finding. The most common mediastinal location is subcarinal (Figs. 6-29, 6-30, 6-31). CT scans show the mass to have a thin or nearly imperceptible wall and to contain fluid, often of water attenuation. Occasionally, the fluid has a higher attenuation than water because of the presence of proteinaceous material or calcium (see also Chapter 6). The contents of the cyst do not enhance after administration of intravenous contrast material.

Congenital cystic adenomatoid malformation (CCAM) is a hamartomatous abnormality of the lung consisting of a multicystic mass of pulmonary tissue in which there is proliferation of bronchial structures at the expense of alveolar development. Three types have been described. Type 1, the most common type, consists of single or multiple large cysts (up to 10 cm in diameter). Type 2 consists of multiple small cysts (1 to 2 cm in diameter), and type 3 (solid form) is a large, noncystic lesion. The prognosis worsens from type 1 to type 3, in part because of associated anomalies that occur with greater frequency with types 2 and 3.

The radiographic appearance varies, depending on the type of lesion. The most common presentation is that of a mass of numerous air-containing cysts that expand the ipsilateral hemithorax and shift the mediastinum to the contralateral side. Occasionally, one cyst preferentially expands, creating a single large lucent area that is similar in appearance to congenital lobar emphysema. Type 3 lesions present as large homogeneous masses, without cystic spaces. Although most cases of CCAM present in the first month of life, the diagnosis is occasionally delayed until adulthood (2). Adult patients commonly present with persistent or recurrent pneumonia. Chest CT in adults with CCAM shows cystic lesions of variable size, most commonly in a lower lobe, which can mimic cystic bronchiectasis, intralobar pulmonary sequestration, intrapulmonary bronchogenic cyst, or prior infection with pneumatocele formation (3).

Bronchopulmonary sequestration consists of nonfunctioning lung tissue, usually cystic and often masslike, that has an anomalous systemic blood supply, usually from the aorta, and no normal communication with the tracheobronchial tree. This disorder is classified into two types: intralobar (the more common type) and extralobar (4). Both types occur most commonly in the posterior basal segment of a lower lobe, usually on the left. Intralobar sequestration is contiguous with normal lung parenchyma, has no separate pleural investment, receives arterial supply most commonly from the aorta, has venous drainage most commonly into a pulmonary vein, and is only rarely associated with other anomalies (Figs. 16-2 and 16-3). Extralobar sequestration is related to a hemidiaphragm (usually the left), and it is often situated between the inferior surface of the lower lobe and the diaphragm, or below the diaphragm. It has a pleural investment separate from the rest of the lung; receives arterial supply from the aorta but usually has venous drainage into the systemic venous system (e.g., inferior vena cava, azygos vein, or portal vein); and is often associated with other congenital anomalies (most commonly eventration or paralysis of the ipsilateral diaphragm and left diaphragmatic hernia) (Fig. 16-4). The classic radiographic appearance of pulmonary sequestration is recurrent or persistent abnormal opacity in a lower lobe that never completely clears. The diagnosis can be confirmed by showing the systemic arterial supply, either with magnetic resonance imaging or CT angiography (5). In adults, this disorder is often discovered incidentally.

Also referred to as the scimitar syndrome or hypogenetic lung syndrome, pulmonary venolobar syndrome is a form of partial anomalous pulmonary venous return that is accompanied by ipsilateral lung hypoplasia. The anomalous venous return is commonly to the inferior vena cava (Fig. 16-5). The hypoplastic lung (which is almost always right sided) is supplied partly or completely by systemic arteries. The ipsilateral pulmonary artery is diminutive. Associated cardiovascular anomalies are frequent, the most common being atrial septal defect (6). Other associated anomalies include pulmonary sequestration, absence of the inferior vena cava, and accessory diaphragm. Less commonly, the syndrome may involve tracheal trifurcation, eventration and partial absence of the diaphragm, phrenic cyst, horseshoe lung, anomalous superior vena cava, and absence of the left pericardium (7). Bronchial anomalies are common, particularly isomerism (identical right and left branching patterns). The anomalous vein is usually visible on frontal chest radiographs as a broad, gently curved shadow descending to the diaphragm just to the right of the heart (Figs. 16-6 and 16-7). The shadow is shaped like a Turkish sword (a scimitar); thus, the designation scimitar syndrome. Other radiographic findings include a small ipsilateral hemithorax with diminished pulmonary vascularity, shift of the mediastinum toward the involved side, and, often, indistinctness of the cardiomediastinal border on the involved side. The lateral radiograph usually
shows a retrosternal band of opacification, which is secondary to the shortening of the anteroposterior diameter of the involved lung, and contact of the anterior involved lung with a rotated and shifted mediastinum (8). Anomalous pulmonary venous return can also be an isolated finding, unassociated with other anomalies (Fig. 16-8).

A pulmonary AVM or congenital arteriovenous fistula is an abnormal vascular communication between a pulmonary artery and a pulmonary vein. The etiology is thought to be defective development of the terminal capillary loops, resulting in the formation of thin-walled, dilated vascular spaces, usually supplied by one distended artery and drained by one distended vein. Pulmonary AVMs are multiple in 33% to 50% of patients and are bilateral in 8% to 20% (1). Approximately 60% of pulmonary AVMs occur in patients with Rendu-Osler-Weber disease (also known as hereditary hemorrhagic telangiectasia; see also Chapter 7). Chest radiographs and CT scans show round or oval, well-defined nodules, which can be lobulated, ranging in size from less than 1 cm to several centimeters in diameter, with prominent feeding and draining vessels (see Figs. 7-32 and 7-33). Although typically incidental findings in adults, AVMs can cause physiologic right-to-left shunting if large, which can result in paradoxical septic emboli.

Bronchial atresia is an uncommon focal obliteration of the proximal portion of a segmental bronchus. It occurs most commonly in the left upper lobe, followed by the left lower lobe and the right middle lobe (9). It is thought to be related to a vascular insult early in development. Mucoid impaction in the airway distal to the obliterated portion is usually seen radiologically as an ovoid, round, or branching tubular structure. The distal lung, aerated by collateral air drift, is typically hyperlucent and hyperinflated and has decreased vascular markings. Bronchial atresia is often discovered incidentally. Bronchoscopy
is usually required to exclude an endobronchial neoplasm.