they vary in size from that of a large vesicle to that of a large grape fruit. Bullae are formed in the lungs of patients afßicted with vesicular emphysema; blebs are present in cases of interstitial emphysema. A bleb is formed by the rupture of the alveolar wall; the air escaping through the tear separates the pleura from the alveolar wall lying underneath it, much like a dissecting aneurysm [46] (Figs. 12.9 and 12.10).

Symptoms and Signs

Symptoms and Signs

Pulmonary sequestrations in adults are usually asymptomatic and the abnormality is found incidentally on a chest radiograph or CT. The most common clinical manifestations are related to superimposed infection, in which cases the signs and symptoms are those of acute pneumonia.

CT Findings

Blebs and bullae rarely cause respiratory symptoms until pneumothorax or giant bullae develop. Many patients are clinically silent. Shortness of breath and nonspeciÞc chest discomfort due to compression of surrounding lung tissue can occur in giant bullae.

CT Findings

See the deÞnition of bulla and bleb (Figs. 12.9, 12.10, and 12.11).

CT-Pathology Comparisons

The most common CT Þndings of intralobar pulmonary sequestration consist of focal areas of lucency or irregular cystic spaces with or without ßuid [50]. Extralobar sequestration is visualized as a homogeneous opacity or wellcircumscribed mass or occasionally cystic areas on CT [50]. The vast majority are situated in the posterior basal segment of a lower lobe. Demonstration of the systemic arterial supply is essential for the diagnosis and this anomalous vessel is typically seen coursing from the lower thoracic or upper abdominal aorta through the inferior pulmonary ligament into the sequestered lung [44] (Fig. 12.12).

CT-Pathology Comparisons

Also see the deÞnition of bulla and bleb.

Patient Prognosis

No therapy is necessary for asymptomatic patients. Patients with large bullae should receive surgical bulla resection. If resection is not possible, they should have regular follow-up to prevent potential acute complications such as pneumothorax and to exclude the development of lung cancer associated with pulmonary bullae. With smoking cessation and optimization of bronchodilator therapy, resolution of giant bullae has been reported [47].

Pulmonary Sequestration

Pathology and Pathogenesis

Pulmonary sequestration is a malformation in which a portion of lung is detached from the remaining normal lung and receives its blood supply from a systemic artery. The anomaly may be intralobar or extralobar. Pathologically, intralobar sequestrations are located within normal lung but are generally well demarcated from the surrounding parenchyma and do not communicate with the normal bronchi [48]. Venous drainage is almost always via the pulmonary venous system. Extralobar sequestrations are completely enclosed by a pleural membrane [49]. Venous drainage of extralobar sequestrations is via systemic veins.

Pathologically, intralobar sequestrations usually consist of one or more cystic spaces resembling dilated bronchi with a variable amount of intervening solid tissue. Therefore, they appear as cystic spaces with or without ßuid on CT. Extralobar sequestration usually contain immature lung tissue and few airways and are completely enclosed by a pleural membrane, so they appear as a well-circumscribed mass on CT.

Patient Prognosis

Surgical resection is the treatment of choice for patients with infection or symptoms resulting from compression of normal lung tissue [51]. Reported postoperative complications are uncommon and the prognosis following surgical excision is excellent [52].

Congenital Cystic Adenomatoid

Malformation

Pathology and Pathogenesis

CCAM is characterized by a multicystic mass, a pulmonary tissue with an abnormal proliferation of bronchial structures [53]. Three main morphologic subtypes (type I, large, multiloculated cysts greater than 2 cm in diameter; type II, uniform small cysts less than 2 cm in diameter; type III, solid appearing lesions that microscopically demonstrate tiny cysts) have been described (Fig. 12.13).