Fig. 53.1
Intraoperative photograph showing a large feeding vessel for extralobar pulmonary sequestration associated with a large paraesophageal hernia
Pulmonary sequestrations usually get their blood supply from the thoracic aorta.
Intrapulmonary sequestration drains via pulmonary veins while extra pulmonary sequestration drains to the IVC.
Intrapulmonary sequestrations are the most common form , and 60 % of these are found in the posterior basal segment of the left lower lobe.
Overall, 98 % of pulmonary sequestrations occur in the lower lobes.
The left lower lobe is the most common site.
Bilateral involvement is uncommon.
About 10 % of cases may be associated with other congenital anomalies.
In the extrapulmonary sequestration, males are affected approximately four times more often than females.
The incidence is equal in males and females in intrapulmonary sequestration.
Embryology
The most commonly accepted theory of pulmonary sequestration formation is based on an accessory lung bud that develops from the ventral aspect of the primitive foregut.
The pluripotential tissue from this additional lung bud migrates in a caudal direction with the normally developing lung.
It receives its blood supply from vessels that connect to the aorta and cover the primitive foregut.
These attachments to the aorta remain and subsequently form the systemic arterial supply of the sequestration.
Early embryologic development of the accessory lung bud results in formation of the sequestration within normal lung tissue (intrapulmonary sequestration).
The intrapulmonary sequestration is encased within the same pleural covering.
In contrast, later development of the accessory lung bud results in the development of extrapulmonary sequestration that may give rise to communication with the gastrointestinal tract.
The extrapulmonary sequestration is encased with its own pleura.
Both types of sequestration usually have arterial supply from the thoracic or abdominal aorta.
Rarely, the celiac axis, internal mammary, subclavian, or renal artery may be involved.
Intrapulmonary sequestration occurs within the visceral pleura of normal lung tissue and usually has no communication with the tracheobronchial tree.
The most common location of intrapulmonary sequestration is in the posterior basal segment, and nearly two-thirds of pulmonary sequestrations appear in the left lung.
Venous drainage for intrapulmonary sequestration is usually via the pulmonary veins, foregut communication is very rare, and associated anomalies are uncommon.
Extrapulmonary sequestration is completely enclosed in its own pleural sac.
Extrapulmonary sequestration may occur above, within, or below the diaphragm, and nearly all appear on the left side.
No communication with the tracheobronchial tree occurs in extrapulmonary sequestration.
Venous drainage for extrapulmonary sequestration is usually via the systemic venous system and foregut communication and associated anomalies, such as diaphragmatic hernia, are more common .
Classification
Sequestrations are classified anatomically into two types .
Intralobar Sequestration
Intralobar sequestration is located within a normal lobe and lacks its own visceral pleura as it lies within the same visceral pleura as the lobe in which it occurs .
The arterial supply is derived from the descending thoracic aorta (75 %), upper abdominal aorta or celiac axis (21 %), or the intercostal arteries (4 %).
The venous drainage is usually to the left atrium via pulmonary veins (95 %) or via the inferior vena cava, superior vena cava, or azygous vein (5 %).
Intralobar sequestration accounts for 75 % of all sequestrations.
Males and females are equally affected.
Intralobar sequestration is usually located in the paravertebral region in the posterior segment of the left lower lobe.
Intralobar sequestration is rarely associated with other developmental abnormalities.
Patients with Intralobar sequestration usually present late in adolescence or adulthood with recurrent chest infection .
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