UPDATED: This medical term is formed by the prefix [retr-] meaning “posterior”, the root term [-periton-] meaning “peritoneum”, and the adjectival suffix [-eal], meaning “pertaining to”. In the strictest sense, the term [retroperitoneal] means “posterior to the peritoneum”.

In practical terms in anatomy and surgery, this term refers to two situations:

In the first acception of the term, it refers to anatomical structures that are truly posterior to the peritoneum, between the peritoneum and the posterior abdominal wall, as are the kidneys, ureters, abdominal aorta, inferior vena cava, etc.

In the second acception of the term, it refers to digestive system structures that although posterior to the parietal peritoneum, they are also attached to the posterior abdominal wall by the peritoneum, fixating them to the posterior abdominal wall. These structures are immobilized in position by the peritoneum. When a surgeon needs to work on one of these “retroperitoneal” digestive system structures they need to render them mobile detaching them from the posterior abdominal wall by incising the peritoneum and “mobilizing “these structures.

There are three segments of the digestive system that are retroperitoneal (ergo, fixated to the posterior abdominal wall by the parietal peritoneum):

• the duodenum, except for its first inch
• the ascending colon
• the descending colon