Bronchopulmonary Sequestration

• Bronchopulmonary sequestration (BPS) is a rare congenital malformation of the lower respiratory tract.

• It consists of a nonfunctioning mass of normal lung tissue that lacks normal communication with the tracheobronchial tree, and that receives its arterial blood supply from the systemic circulation.

• BPS is estimated to comprise 0.15 to 6.4 percent of all congenital pulmonary malformations, making it an extremely rare disorder.

• Sequestrations are classified anatomically.

  • Intralobar sequestration (ILS) in which the lesion is located within a normal lobe and lacks its own visceral pleura.

  • Extralobar sequestration (ELS) in which the mass is located outside the normal lung and has its own visceral pleura

• The blood supply of 75% of pulmonary sequestrations is derived from the thoracic or abdominal aorta.

  • The remaining 25% of sequestrations receive their blood flow from the subclavian, intercostal, pulmonary, pericardiophrenic, innominate, internal mammary, celiac, splenic, or renal arteries.

Intralobar sequestration

·          The intralobar variety accounts for 75 percent of all sequestrations.

·          Usually presents in adolescence or adulthood as recurrent pneumonias.

·          Lies within the same visceral pleura as the lobe in which it occurs.

·          Males and females are equally affected with ILS.

·          In ILS, the arterial supply usually is derived from the lower thoracic or upper abdominal aorta.

·          Venous drainage is usually to the left atrium via pulmonary veins establishing a left to right shunt.

o        Abnormal connections to the vena cava, azygous vein, or right atrium may occur.

·          Two thirds of the time, the sequestration is located in the paravertebral gutter in the posterior segment of the left lower lobe.

·          Unlike extralobar sequestration, it is rarely associated with other developmental abnormalities.

·          Patients present with signs and symptoms of pulmonary infection of a lower lobe mass.

o        It is believed that sequestrations become infected when bacteria migrate through the pores of Kohn or if the sequestration is incomplete.

Extralobar sequestration

·          The extralobar variety accounts for 25 percent of all sequestrations.

·          ELS usually presents in infancy with respiratory compromise.

·          Develops as an accessory lung contained within its own pleura.

·          ELS has a male predominance (80%).

·          Related to the left hemidiaphragm in 90% of cases.

o        ELS may present as a subdiaphragmatic or retroperitoneal mass.

·          In general, the arterial supply of ELS comes from an aberrant vessel arising from the thoracic aorta.

·          It usually drains via the systemic venous system to the right atrium, vena cava, or azygous systems.

·          Congenital anomalies occur more frequently in patients with ELS than ILS.

o        Associated anomalies include Congenital cystic adenomatoid malformation (CCAM), congenital diaphragmatic hernia, vertebral anomalies, congenital heart disease, pulmonary hypoplasia, and colonic duplication

·          Since it is enveloped in its own pleural sac, it rarely gets infected so almost always presents as a homogeneous soft tissue mass.

·          The mass may be closely associated with the esophagus, and fistulae may develop.

Imaging

·          An arteriogram has been considered vital in documenting the systemic blood supply, allowing definitive diagnosis as well as preoperative planning.

·          The advent of new noninvasive imaging techniques has changed this thinking.

Chest radiograph

·          Sequestrations typically appear as a uniformly dense mass within the thoracic cavity or pulmonary parenchyma.

·          Recurrent infection can lead to the development of cystic areas within the mass.

·          Air-fluid levels due to bronchial communication can be seen.

Ultrasound

·          The typical sonographic appearance of BPS is an echogenic homogeneous mass that may be well defined or irregular.

·          Some lesions have a cystic or more complex appearance.

·          Doppler studies are helpful to identify the characteristic aberrant systemic artery that arises from the aorta and to delineate venous drainage.

CT

·          CT scans have 90% accuracy in the diagnosis of pulmonary sequestration.

·          The most common appearance is a solid mass that may be homogeneous or heterogeneous, sometimes with cystic changes.

·          Less frequent findings include a large cavitary lesion with an air-fluid level, a collection of many small cystic lesions containing air or fluid, or a well-defined cystic mass.

·          Emphysematous changes at the margin of the lesion are characteristic and may not be visible on the chest radiograph.

·          CT technique for optimal depiction of lesions by using state-of-the-art volumetric scanning requires a fast intravenous (IV) contrast injection rate and appropriate volume and delay based upon size.

·          Multiplanar and 3D reconstructions are helpful. 

MRI

·          Contrast-enhanced MRA or even conventional T1-weighted spin-echo (SE) images may help in the diagnosis of pulmonary sequestration by demonstrating a systemic blood supply, particularly from the aorta, to a basal lung mass.

·          In addition, MRA may demonstrate venous drainage of the mass and may obviate more invasive investigations.

·          However, CT allows sharper delineation of thin-walled cysts and emphysematous changes than MRI.