The retroperitoneal space is the part of the abdominal cavity that lies behind the peritoneum, a membrane that typically lines the inside of the abdomen. Inside the retroperitoneal (deep to the peritoneum) space, there are the kidneys, adrenal glands, bladder, and ureters. The aorta and inferior vena cava vessels are located within the space as well as part of the esophagus and rectum. These are called the primary retroperitoneal organs, meaning they typically form during gestation behind the peritoneum and remain there throughout development. All of the organs in the space typically feature some peritoneum tissue attached to their front, or anterior side, although no anatomical structures are generally a part of this space.