Pulmonary
Sequestration
Pulmonary
sequestration is a congenital malformation in which a mass of pulmonary tissue
has no connection either to the parent tracheobronchial tree or the pulmonary
vascular tree and receives its blood supply from a systemic artery. The
systemic artery usually arises from the aorta either above or below the
diaphragm; occasionally from an intercostal artery; or, rarely, from the
brachiocephalic (innominate) artery. The sequestered tissu presents itself in
two forms: intralobar and extralobar.
Intralobar Sequestration
This type comprises a nonfunctioning portion of lung
within the visceral pleura of a pulmonary lobe. In the majority of cases, it
derives its systemic arterial supply from the descending thoracic aorta or the
abdominal aorta. The venous drainage is invariably by way of the pulmonary
veins, producing an arterio-arterial communication. Embryologically, it appears
to be a failure of the normal pulmonary artery to supply a peripheral portion
of the lung; hence, the arterial supply is derived from a persistent ventral
branch of the primitive dorsal aorta.
Extralobar Sequestration
This malformation may represent a secondary and more
caudal development from the primitive foregut that is then sealed off and
migrates caudally as the lung grows. Venous drainage is to the systemic
circulation, usually the azygos, hemiazygos, or caval veins. Anatomically, it
is related to the left hemidiaphragm in more than 90% of cases. It may be
situated between the diaphragmatic surface of the lower lobe and the diaphragm
or within the substance of the diaphragm.
On pathologic examination, the affected mass is
cystic, and the spaces are filled either with mucus or, if infected, with
purulent material. The cystic spaces are lined by either columnar or flat
cuboidal epithelium.
Only 20% of intralobar sequestrations present in the
neonatal period; occasionally, there may be heart failure caused by massive
arteriovenous shunting. Extralobar sequestration rarely presents in the
neonatal period but may be found incidentally at operation to repair a
congenital diaphragmatic hernia. Later presentations include secondary
infection, pneumonia, pleural effusion, and empyema. When the sequestered lung becomes infected, it
often appears to be a chronic pulmonary abscess accompanied by episodes of
fever, chest pain, cough, and bloody mucopurulent sputum.
On antenatal ultrasonography, the abnormal lung can be
seen as an echogenic intrathoracic or intra-abdominal mass. In 50% of cases,
there is a pleural effusion, and polyhydramnios is a frequent complication.
Postnatally, on radiographic examination the diagnosis should be suspected if there is a dense lesion on the
posteromedial part of the left zone of the chest radiograph. Extralobar
sequestration is usually seen as a dense triangular lesion close to the
diaphragm.
Treatment for either type consists of surgical resection.
Because of the threat of secondary infection and hemorrhage, surgery should be
recommended even though the patient is asymptomatic at the time. When infection occurs, complete removal is mandatory.
