extraperitoneal

Extraperitoneal is an anatomical term describing tissues or spaces located outside the peritoneal cavity. In contrast to intraperitoneal structures that are enveloped by peritoneum, extraperitoneal tissues lie between the peritoneum and the abdominal or pelvic walls, or behind the peritoneum in the retroperitoneal space. The extraperitoneal region therefore includes the retroperitoneal space, which lies posterior to the peritoneum and contains organs such as the kidneys, adrenal glands, pancreas (except the tail), portions of the duodenum, major vessels, and the aorta and inferior vena cava, as well as surrounding fat and connective tissue. It also includes the preperitoneal space, a potential interval between the peritoneum and the abdominal wall in the anterior abdomen.

Clinically, the distinction matters for disease spread, imaging interpretation, and surgical technique. Extraperitoneal infections or hematomas may track along the retroperitoneal space and present with atypical symptoms. In surgery, extraperitoneal or preperitoneal approaches place implants or perform dissection without opening the peritoneal cavity, as in some hernia repairs and in extraperitoneal radical prostatectomy. Imaging modalities such as CT or MRI distinguish extraperitoneal pathology from intraperitoneal disease, guiding management.

The term is sometimes used interchangeably with retroperitoneal for parts of the anatomy that lie behind the peritoneum, though retroperitoneal is a more specific subset of the extraperitoneal space. Understanding extraperitoneal anatomy is important in planning surgical access and interpreting abdominal pain or mass effects.