Retroperitoneum (Latin)

Retroperitoneal organs (organa retroperitonealia) are found posterior to the cavitas peritonealis in the spatium retroperitoneale, with only their anterior wall covered by the peritoneum parietale. If they develop and remain outside the peritoneum, they are referred to as the primary retroperitoneal organs: these include the kidneys (renes), suprarenal glands (glandulae suprarenales), ureters (ureteres), aorta/vena cava inferior and rectum. Secondary retroperitoneal organs initially develop within the peritoneum, however become retroperitoneal as they lose their mesentery during embryonic development: the include the pancreas, pars distalis duodeni, colon ascendens and colon descendens.