Atypical extralobar sequestration: CT-pathological correlation.

Pulmonary sequestration is a malformation comprised of dysplastic lung tissue without normal communication with the tracheobronchial tree and with an anomalous systemic arterial supply. Pulmonary sequestration is classified into two types, intralobar and extralobar based on the location of the malformation and the venous drainage. Extralobar sequestration is less common than intralobar sequestration and usually has systemic venous drainage into the azygos system. Most patients with extralobar sequestration are diagnosed before the age of 10. We present an interesting and unusual case of extralobar sequestration which presented as a retroperitoneal mass in an asymptomatic adult.