Bronchopulmonary Sequestration
Submitted by Samir Jethra, MSIV

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.
• Abnormal connections to the vena cava, azygos 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.
• 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.
• 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 azygos systems.
• Congenital anomalies occur more frequently in patients with ELS than ILS.
• 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.

Intralobar Sequestration, Right Lower Lobe. There is a mass in the right lower lobe (white arrows) which is drawing its blood supply (red arrows) from the descending aorta. Drainage was back to the pulmonary veins.

Grainger & Allison's Diagnostic Radiology: A Textbook of Medical Imaging, 4th ed., 2001 Churchill Livingstone, Inc. pp 654-655. 

Khan, Ali Nawaz, Bronchopulmonary Sequestriation, e-Medicine, http://www.emedicine.com/radio/topic585.htm.  

Oermann, Christopher M, Bronchopulmonary Sequestration, Up to Date, http://www.utdol.com/application/topic.asp?file=pedipulm/10425&type=P&selectedTitle=4~6