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Bronchopulmonary Sequestration

 
 

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.

 

 

 CT with IV contrast of the thorax showing an Intralobar Bronchopulmonary Sequestration.  The yellow arrow in frames A and B point to a hyperdense region in the left lower lobe of the lung with small cystic lesions containing air within it.  The red arrows in frames C and D show a contrast enhanced vessel arising from the aorta and supplying the area of hyperdensity in the lung.

Click here for a larger version of the same photo

 

 

 

REFERENCES

Wikipedia