Extralobar Pulmonary Sequestration

General: Discrete masses of pulmonary parenchyma located outside the normal pleura, not connected to the tracheo-bronchial tree, and usually supplied by a branch of the thoracic or abdominal aorta (~75%) with drainage into the systemic circulation (~80%). Presumably originate from the foregut, separate from the normally developing lung. They are diagnosed prenatally in ~25% of cases, and ~60% present by 3 months, often with cyanosis, dyspnea, and/or difficulty feeding, with ~10% asymptomatic. Sometimes associated with hydrops, anasarca, polyhydramnios, bronchogenic cyst, bronchopulmonary-foregut connection, cardiovascular malformations, pectus excavatus, diaphragmatic hernia, or pulmonary hypoplasia. Prognosis is good for small sequestrations but the associated pulmonary hypoplasia with large sequestrations may be severe to fatal.

Gross: Usually a single round to ovoid lobule ranging from 0.5~15cm, with about half in the left hemithorax and the remainder spread among right hemithorax (~20%), mediastinum, and below the diaphragm (~18%). Covered by a smooth to wrinkled pleura overlying a reticular lymphatic network, which may be prominent. Cut surface shows grossly normal homogenous pink to tan tissue or clusters of small cysts.

Microscopic: Uniformly dilated & tortuous bronchioles, alveolar ducts, and alveoli in a normal acinar pattern. Bronchioles have an undulating cuboidal to columnar epithelium. ~50% of cases consist of back-to-back, dilated, bronchiole-like structures resembling congenital pulmonary airway malformation Type 2. Lymphatics usually unremarkable, but are occasionally so prominent as to resemble congenital pulmonary lymphangiectasia. Infarction, infection, inflammation/arteritis are rare.

Stains:

• Positive:
• Negative:
• Suggested, focused panel:

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