Retroperitoneal space

The retroperitoneal space (retroperitoneum) is the anatomical space (sometimes a potential space) in the abdominal cavity behind the peritoneum.

It has no specific delineating anatomical structures.

Organs are retroperitoneal if they have peritoneum on their anterior side only. Structures that are not suspended by mesentery in the abdominal cavity and that lie between the parietal peritoneum and abdominal wall are classified as retroperitoneal.

Retroperitoneal structures

Structures that lie behind the peritoneum are termed "retroperitoneal". Organs that were once suspended within the abdominal cavity by mesentery but migrated posterior to the peritoneum during the course of embryogenesis to become retroperitoneal are considered to be secondarily retroperitoneal organs.

• Primarily retroperitoneal, meaning the structures were retroperitoneal during the entirety of development:
  • urinary
    • adrenal glands
    • kidneys
    • ureter
  • circulatory
    • aorta
    • inferior vena cava
  • digestive
    • esophagus (thoracic part, part inside abdominal cavity is intraperitoneal)
    • rectum (part, lower third is extraperitoneal)
• Secondarily retroperitoneal, meaning the structures initially were suspended in mesentary and later migrated behind the peritoneum during development:
  • the head, neck, and body of the pancreas (but not the tail, which is located in the splenorenal ligament)
  • the duodenum, except for the proximal first segment, which is intraperitoneal
  • ascending and descending portions of the colon (but not the transverse colon, sigmoid or the cecum)

Retroperitoneal structures