Pulmonary sequestration is an uncommon congenital usually cystic mass of non-functioning primitive lung tissue that does not communicate with the tracheobronchial tree or the pulmonary arteries. It is supplied by an anomalous artery arising from aorta & venous drainage is via the azygos system, pulmonary veins or the inferior vena cava.

The two forms of pulmonary sequestration include, intrapulmonary which is surrounded by normal lung tissue & extra pulmonary which has its own pleural investment.

In intralobar PS, the pulmonary tissue is isolated from the normal lung

tissue; however, the pleural covering remains contiguous with that of the lung. The left lung is commonly involved. Typically, the mass is confined to the posterior basilar segments of the lower lobe of the lung. There are rarely associated anomalies or foregut communications. The arterial supply is via a systemic artery and the venous drainage is through the pulmonary veins.

Extralobar PS is contained within its own pleural sac and is separated from the rest of the lung. It may be located between the inferior surface of the lower lobe and diaphragm, below the diaphragm, within the diaphragm, or in the mediastinum. It occurs on the left in greater than 90% of the cases. There may be an occasional foregut communication and associated anomalies are quite common like diaphragmatic hernia, cardiovascular malformation, bronchogenic cyst, pectus excavatum, or other lung anomalies. The arterial supply is from a systemic artery and the venous drainage is typically via the systemic veins, rather than the pulmonary veins as seen in intralobar PS.

- If no communication between sequestration and normal lung tissue is present, radiography usually reveals a dense opacity in the posterior basal segment of the lower lobe. A cystic appearance may also be observed.

- Lesion density often increases with secondary infection and appears as a uniform consolidation. Distinguishing an intrapulmonary sequestration from extrapulmonary sequestration is difficult using plain radiography.

- Intrapulmonary lesions tend to be heterogeneous and are not well defined. Extrapulmonary masses are usually observed as solid, well defined, and retrocardiac.

CT scanning, with its superior spatial resolution, yields the most information about the bronchial anatomy and the pulmonary parenchymal lesion.

Presence of systemic arteries revealed by chest imaging is the major diagnostic feature of pulmonary sequestration. CT scanning with contrast or magnetic resonance angiography (MRA) have been very useful. The arterial supply and venous drainage both should be outlined because of the unpredictability of vascular connections. CT angiography is helpful in identifying aberrant systemic arterial supply and 3-dimensional rendering of multidetector row CT can reveal venous drainage.

Real-time ultrasonography and Doppler imaging are reliable