The retroperitoneal space lies on the posterior abdominal wall behind the parietal peritoneum. It extends from the 12th thoracic vertebra and the 12th rib to the sacrum and the iliac crests below. The floor or posterior wall of the space is formed from medial to lateral by the psoas and quadratus lumborum muscles and the origin of the transversus abdominis muscle. Each of these muscles is covered on the anterior surface by a definite layer of fascia.
In front of the fascial layers is a variable amount of fatty connective tissue that forms a bed for the suprarenal glands, the kidneys, the ascending and descending parts of the colon, and the duodenum. The retroperitoneal space also contains the ureters and the renal and gonadal blood vessels.