- To review the imaging characteristics of retroperitoneal anatomy. - To provide an overview of the most frequent differential diagnosis of retroperitoneal pathologies.

ANATOMY We can divide the abdominopelvic cavity into three anatomical spaces: intraperitoneal cavity, retroperitoneum, and pelvis. These spaces are not independent and are communicated with each other through fasciae or anatomical defects. The retroperitoneum extends from the diaphragm to the pelvis and is bounded anteriorly by the posterior parietal peritoneum and posteriorly, medially and laterally, by the transversalis fascia that covers the muscles (lumbar quadratus, psoas and transverse abdominal). Within the retroperitoneum, the anterior and posterior renal fascia form three dis­tinct compartments: the posterior pararenal...

IMAGING TECHNIQUES - Ultrasonography (US), can be used as an initial imaging modality for the evaluation of abdominal pain or palpable abdominal masses. Is less useful for evaluating the entire abdomen and pelvis, because has a limited depth of penetration. - Multidetector Computed Tomography (MDCT), is the most widely used cross-sectional imaging modality for the abdomen and pelvis, being the method of choice in the evaluation of the peritoneal cavity and the retroperitoneal anatomy. Plays an integral role in the characterization of the retroperitoneal masses,...

It is essential that we are familiar with the retroperitoneal anatomy, the different spaces, and their bound­aries because knowledge of these structures is important to understand the pathologic processes, localize the disease, help to formulate a differential diag­nosis and make an accurate reporting. MDCT with coronal and sagittal reformations fully delineate the peritoneal anatomy and extent of disease. A variety of pathologies in the retroperitoneum may demonstrate nonspecific radiologic features, but some of them, like the liposarcoma, have typical characteristics.

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