Pulmonary Sequestration

Pulmonary sequestration is a condition in which a segment or lobe of dysplastic lung tissue exists with no communication with the rest of the tracheobronchial tree and receives an anomalous systemic vascular supply, separate from the rest of the lung. It is, therefore, a nonfunctional tissue. The condition was first described by Pryce as early as 1946. Although Rokitansky and Rektorik described a similar clinical finding way back in 1861. Pryce originally divided pulmonary sequestration into: Intralobar and extralobar. They further subdivided Intralobar into 3 types. Intralobar sequestration is characterized by its presence within the visceral pleura of the functioning lung. Venous drainage is into the pulmonary vein.  It is more common in the left lower lobe. Approximately two-thirds of intralobar sequestrations are found in the posterior basal segment of the left lower lobe. It is more common and has a reported incidence of 75% to 86% among all cases of sequestration. An exception to the left-sided preponderance is pulmonary sequestrations associated with Scimitar syndrome (partial anomalous pulmonary venous connection), where right-sided lesions are more common. Extralobar sequestration has a separate visceral pleura and venous drainage. Venous drainage is into the systemic veins, frequently the lower lobe vein, azygos vein, or hemiazygos vein. There have been reported cases of drainage into the subclavian or portal vein as well. Arterial supply is from systemic vessels–most commonly descending thoracic aorta (73%)  as reported by Savic et al., the cranial portion of the abdominal aorta, celiac trunk, splenic artery (21%), as well as intercostal arteries. Rare cases of arterial supply from pericardiophrenic, right coronary artery, subclavian, and internal thoracic arteries have been reported. They are often found between the diaphragm and the lower lobes and rarely infra- diaphragmatically. In spite of the overall male prevalence of pulmonary sequestration, intraabdominal sequestration is most often found in women (75%), usually as a left retroperitoneal mass.