Pulmonary sequestration is non-functioning dysplastic lung tissue separated from the tracheobronchial tree and with systemic blood supply. The typical location is lower lobe and more frequently on the left.

Pulmonary sequestrations are classified as intralobar or extralobar. The former do not have a separate pleural lining and commonly drain into the left atrium, whereas the latter are lined by a pleural membrane, commonly drain into systemic veins and can be infra-diaphragmatic.

The main differential diagnosis includes congenital pulmonary airway malformation which has a pulmonary arterial blood supply.