pulmonary sequestration

pulmonary sequestration

pulmonary sequestration
note the unilateral, well-defined, solid echogenic mass displacing the heart. a pleural effusion is also present.
pulmonary sequestration
transverse and sagittal views of the chest demonstrate a largely homogeneous echogenic mass in the right posterior hemithorax, displacing adjacent structures; there is no associated hydrops; colour and pulsed wave doppler show its relation to the aorta and aberrant venous drainage.

description

this bronchopulmonary foregut malformation represents an ectopic, non-functioning portion of lung parenchyma which has its own specific blood supply but no bronchial connection with the lung.

it exists in two forms:

  1. intralobar, indicating that it lies within the pulmonary visceral pleura.
  2. extralobar, lying outside the pulmonary visceral pleura with its own pleural covering.

the specific form depends on the timing of the development of supernumerary lung buds in relation to pleural development, which occurs at 6 weeks.if these develop before pleural development they will be intralobar. if subsequent to this, they will be extralobar.

a male:female preponderance of 4:1 exists.

diagnosis

the sonographic appearance will depend on the form of sequestration:

  1. intralobar pulmonary sequestration is typically defined by a unilateral, solid, non-pulsatile, echogenic, well-defined (triangular or conical) intrathoracic mass with no acoustic shadowing. the lesion is commonly left-sided (90%). displacement of adjacent heart and mediastinum may occur. the arterial blood supply is usually systemic with drainage through the pulmonary veins. pleural effusion may occur, and polyhydramnios occurs in 50% of cases. the fetus may be hydropic due to low output failure secondary to venous obstruction.
  2. extralobar pulmonary sequestration commonly presents as a uniformly echogenic retroperitoneal or upper abdominal mass with margins located between the lower lobe and diaphragm; an intrapericardial location also exists. the arterial supply can come from the renal or adrenal artery, the aorta or inferior phrenic artery, and the venous drainage is also systemic in nature. a small proportion of both forms may have a cystic component.

there is a wide variety of congenital malformations reported in association with pulmonary sequestration but no syndromic associations. some of the reported malformations include pulmonary lobe agenesis, diaphragmatic hernia or eventration, ectopic pancreatic tissue, foregut duplication or diverticulum, congenital absence of the pericardium and arteriovenous fistulas.

differential diagnosis

  • cystic adenomatoid malformation, where depending on the subtype, cysts of varying degrees are present. however the identification of an aberrant blood supply is an important diagnostic feature of pulmonary sequestration.
  • bronchogenic cysts have a largely heterogeneous appearance with poor echogenicity and are usually located in the posterior mediastinum.
  • retroperitoneal teratomas differ from extralobar sequestration in that acoustic shadowing is usually present with teratomas but not with pulmonary sequestration.
  • with neuroblastomas mixed echogenicity is present.
  • congenital diaphragmatic hernia may be excluded by ensuring the integrity of the diaphragm; this is fundamental to the examination of any fetal chest mass.

sonographic features

unilateral echogenic well defined lung mass without acoustic shadowing.

will be associated with an aberrant blood supply on colour flow mapping.

associated syndromes