[Retroperitoneal lipoma through the foramen of Bochdalek detected as a mass of chest roentgenogram: report of a case].

Retroperitoneal lipomas are relatively uncommon. They are generally asymptomatic tumors. We experienced a 70-year-old man who had retroperitoneal lipoma detected as a mass of chest roentgenogram. Transcutaneous needle biopsy yielded a diagnosis of lipoma. We performed surgical resection because the tumor was growing. The complete resection of the tumor was done uneventfully. The pathological diagnosis of the tumor was benign mature lipoma. The sagittal view of the chest MRI gave precise and useful anatomical informations. This tumor was considered to originate from the retroperitoneal fatty tissue at the subdiaphragmatic region and to extend into the posterior mediastinum though the foramen of Bochdalek. We present herein this case because of a unique growing form, which is the first report in the Japanese literature to our knowledge.