An area occupying the most posterior aspect of the ABDOMINAL CAVITY. It is bounded laterally by the borders of the quadratus lumborum muscles and extends from the DIAPHRAGM to the brim of the true PELVIS, where it continues as the pelvic extraperitoneal space.

Retroperitoneal neoplasms are a diverse group of tumors that originate in the retroperitoneal space, which is the area behind the peritoneum and includes the kidneys, adrenal glands, pancreas, and major blood vessels.

A slowly progressive condition of unknown etiology, characterized by deposition of fibrous tissue in the retroperitoneal space compressing the ureters, great vessels, bile duct, and other structures. When associated with abdominal aortic aneurysm, it may be called chronic periaortitis or inflammatory perianeurysmal fibrosis.

Tomography using x-ray transmission and a computer algorithm to reconstruct the image.