Bronchial atresia may be lobar, segmental, or subsegmental, and it may be isolated or associated with systemic arterial connection (intralobar sequestration) and, more rarely, abnormal venous connection. Those cases with systemic arterial connection may occasionally have connection to the gastrointestinal tract (intralobar sequestration and communicating bronchopulmonary foregut malformation).

Isolated bronchial atresia usually involves a segmental bronchus, most commonly in the left upper lobe and rarely in the right upper or lower lobe. Bronchial atresia is said to typically present in late childhood or adolescence with dyspnea, recurrent pneumonia, or as an incidental finding on chest x-ray film. With increasing application of prenatal ultrasonography, diagnosis in utero is becoming more common. Grossly, the atretic bronchus results in a mucocele, which may appear as a bulge at the hilum of the lung. The parenchyma beyond the atresia and mucocele contains abundant mucus and shows other obstructive changes, including airspace enlargement and decreased density of airways and vessels. The distal parenchyma often shows maldevelopment in the form of pulmonary hyperplasia or microcystic maldevelopment. Microcystic maldevelopment occurs in approximately 50% of cases and resembles the small cyst type of congenital cystic adenomatoid malformation (Stocker type II). There may also be superimposed chronic inflammatory infiltrates when diagnosis and definitive surgery are delayed.

Bronchial atresia involving the lower lobes, especially the left lower lobe, is often associated with aberrant systemic arterial connection, forming an “intralobar sequestration” in which a region of parenchyma is functionally isolated from the remainder of the lung. Despite investment by the same pleura, one region of the lobe is “sequestered” from the surrounding parenchyma by both the absence of connection with the tracheobronchial tree and an aberrant vascular supply. The arterial supply may be from single or multiple vessels arising from the distal thoracic or proximal abdominal aorta or the celiac, splenic, intercostal, or subclavian arteries. Although venous drainage is usually by the pulmonary vein, the aberrant vessels may include systemic venous connection. Intralobar sequestration is infrequently associated with other anomalies and is rarely identified at birth, although like other developmental abnormalities of the lung, it is increasingly being recognized by prenatal ultrasonography. The morphologic features of bronchial atresia with systemic arterial connection (intralobar sequestration) are similar to isolated bronchial atresia, including the presence of a mucocele and histologic evidence of obstructive changes with parenchymal maldevelopment.