Pulmonary sequestration is a rare congenital (present from birth) malformation where non-functioning lung tissue is separated from the rest of the lung and supplied with blood from an unusual source, often an artery from systemic circulation. Pulmonary sequestrations may be defined as intralobular or extralobular, depending on their location. Symptoms may include a chronic or recurrent cough, respiratory distress or lung infection. Treatment depends on the location and may involve surgery.

If the accessory lung bud develops early in embryonic development, the pulmonary sequestration occurs among the normal lung tissue, where it is encased within the pleural sac. This results in intralobular pulmonary sequestration. Venous drainage of intralobular pulmonary sequestration is usually through the pulmonary circulation. If the accessory lung bud develops later, extralobular pulmonary sequestration results. This type of pulmonary sequestration is separated from the normal lung tissue by its own visceral pleura and can occur above, within, or below the diaphragm. Venous drainage is usually through the systemic circulation.

Typical symptoms seen in infants with extralobular pulmonary sequestration include cough, respiratory problems, feeding difficulties, or congestive heart failure, although many infants have no symptoms. Chronic infections are not common. Extralobular pulmonary sequestration is commonly associated with other birth defects, including diaphragmatic hernia and other lung malformations such as congenital cystic adenomatoid malformation and bronchogenic cysts, pectus excavatum, pericardial problems, and duplication cysts. This type of sequestration accounts for 25 percent of all sequestrations.

While the vast majority of pulmonary sequestration cases occur in isolation (without any family history), rare familial cases have been reported. Therefore, a genetic component cannot be ruled out.

Due to the risk for infection and bleeding, intralobar pulmonary sequestrations are usually removed, either by segmentectomy (removal of part of the lung) or lobectomy (removal of the full lobe). Angiography along with CT scan (with or without contrast) and MRI are generally used to visualize the origins of the blood supply before surgery is performed.