Retroperitoneal space
anatomical space in the abdominal cavity behind the peritoneum
The retroperitoneal space (retroperitoneum) is the anatomical space (sometimes a potential space) behind (retro) 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.
This is different from organs that are not retroperitoneal, which have peritoneum on their posterior side and are suspended by mesentery in the abdominal cavity.
The retroperitoneum can be further subdivided into the following:
Perirenal (or perinephric) space
Anterior pararenal (or paranephric) space
Posterior pararenal (or paranephric) space
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
anal canal
Secondarily retroperitoneal, meaning the structures initially were suspended in mesentery and later migrated behind the peritoneum during development
the duodenum, except for the proximal first segment, which is intraperitoneal
ascending and descending portions of the colon (but not the transverse colon, sigmoid and the cecum)
pancreas, except for the tail, which is intraperitoneal
Subdivisions
Perirenal space
It is also called the perinephric space. Bounded by the anterior and posterior leaves of the renal fascia. It contains the following structures:
Adrenal gland
Kidney
Renal vessels
Perirenal fat (also "perirenal fat capsule", "perinephric fat, or "adipose capsule of the kidney") is external to the fibrous capsule of the kidney, and internal to the renal fascia (which separates it from the pararenal fat); connective tissue trabeculae extend through it to unite the fibrous capsule of the kidney, and the renal fascia.
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