To describe and illustrate the imaging findings of extraperitoneal compartments and fasciae and to understand the intercommunication between them as well as the pathways of spread of extraperitoneal fluid collections.

The extraperitoneal space is a potential space that surrounds the peritoneal cavity, being defined by parietal peritoneum internally and by transversalis fascia postero-externally (figure 1). It is less developed in the anterior and lateral parts of the abdomen, while it is a large compartment in the pelvis and especially in the posterior abdomen. Its anatomic relationships with the visceral organs of the abdomen and pelvis give the extraperitoneal space a great radiological importance. Extraperitoneal effusions may result from a variety of infectious, neoplastic, inflammatory and...

Pancreatitis The absence of a capsule around the pancreas allows easy access to pancreatic enzymes to spread to multiple anatomic compartments around the pancreas when acute inflammation occurs. Fluid collections are commonly present in the anterior pararenal space, in the interfascial planes, in the lesser sac and in the subperitoneal spaces of transverse mesocolon and of the small bowel mesentery [1,5]. Since the pancreas is mostly located in the anterior pararenal space, the involvement of this retroperitoneal space is typical (figure 5). However, bilateral spread...

The introduction of cross–sectional imaging was essential to understand and to study the extraperitoneal space anatomy and the extent of extraperitoneal disease. The recognition of the anatomic relationships of the extraperitoneal space is important to accurate CT diagnosis and analysis of extraperitoneal pathologic processes.

Mariana Horta Department of Radiology Centro Hospitalar Lisboa Ocidental Estrada do Forte do Alto do Duque 1449-005 Lisboa Portugal

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