Pulmonary sequestration with CCAM type II appearing as adrenal tumor protruding through a Bochdalek hernia

A case of a pulmonary sequestration, which almost exclusively consisted of a congenital cystic adenomatoid malformation type II located subdiaphragmatically in the left retroperitoneal area, is reported. This case, in a 24-year-old male patient, is unique in that it appeared as an adrenal incidentaloma and extended through a Bochdalek hernia into the pleural space. It was discovered upon routine ultrasound screening for hepatocellular carcinoma in a patient with a carrier state for hepatitis B. Diagnosis was established only upon histological analysis of the surgically removed tumor after staining with hematoxylin and eosin as well as surfactant A and B. The location of the tumor may indicate that it was formed by an entrapment of a lung bud by the developing diaphragm. This appearance may give us insight into the formation of such tumors. It also highlights the difficulty of diagnosing subdiaphragmatic retroperitoneal tumors without histological examination.