Pulmonary Sequestration

T. Bernard Kinane, MD

Introduction

•Pulmonary sequestration is a cystic mass that is composed of primitive, nonfunctional lung tissue.

•Pulmonary sequestrations are rare and represent 0.15%–6.0% of all congenital pulmonary malformations.

•Most cases occur sporadically.

•This malformation is separate from the tracheobronchial tree and receives its blood supply from a systemic artery rather than the pulmonary artery.

•Because it fails to connect with the tracheobronchial tree, it does not contribute to respiration.

•There are 2 types of pulmonary sequestration: intralobar and extralobar. Intralobar sequestration occurs within a normal lobe of the lung and accordingly does not have its own visceral pleura. An extralobar sequestration is outside the lung and has its own visceral pleura.

•Intralobar sequestration is the most prevalent of the 2 types and accounts for about 80% of all sequestrations.

•Male and female patients are equally affected by the intralobar type.

•The extralobar type has a male to female ratio of 4:1.

•Only the extralobar type is associated with other congenital anomalies, which occur in about 60% of cases. The anomalies include pulmonary malformations such as congenital pulmonary airway malformation (CPAM), diaphragmatic hernia, and lobar emphysema, as well congenital heart disease.

Pathophysiology

•A sequestration is derived from an accessory lung bud that develops from the primitive foregut. Its blood supply is derived from the aorta and the adjoining vessels.

•Early embryologic development of the accessory foregut bud results in the formation of this additional structure in parallel with the normal lung. This process leads to the formation of a sequestration within normal lung tissue, which results in the intrapulmonary variant. However, later development of the accessory lung bud leads to the formation of the accessory structure outside the normal lung, resulting in the extrapulmonary sequestration.

•On the other hand, the venous drainage of the intralobar sequestration usually occurs via the pulmonary veins to the left atrium, setting up a right to left shunt. Extralobar sequestrations usually drain via systemic veins, such as the vena cava and azygous systems.

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