E2193. Looking Behind the Scenes: Anatomy and Differential Considerations in the Retroperitoneal Spaces
  1. Edwina Chang; Santa Clara Valley Medical Center; Stanford University Medicine
  2. Justin Tse; University of California - Los Angeles
  3. Luyao Shen; Stanford University Medicine
The retroperitoneal space is an anatomically complex space with a myraid of focal, diffuse, benign and malignant pathology. While masses in the retroperitoneum are relatively more rare, understanding the anatomy and determining the appropriate differential considerations are essential to clinical management. Consequently, determining the origin of the mass, the component of the mass and the extent of invasion across the retroperitoneal planes pose diagnostic challenges which will be discussed in this exhibit.

Educational Goals / Teaching Points
- To review the anatomy of the retroperitoneum and the retroperitoneal spaces, including the fascial planes and potential spread between the retroperitoneal and peritoneal planes. - To understand the differential consideration of masses and mass-like lesions in the retroperitoneal spaces, with emphasis on perinephric masses. - To review the imaging characteristics of retroperitoneal masses on CT, MR and US and learn the important tips in using multimodality imaging to aid in diagnosis.

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques
- The exhibit will review the anatomy of the retroperitoneum, including the retroperitoneal spaces and its contents. Modes of potential communication between the retroperitoneum and peritoneum via the fascial planes will be emphasized. - Next, differential diagnosis of retroperitoneal masses and mass-like lesions will be discussed, including neoplasms (such as lymphoma, metastases and sarcomas), hematomas, urinomas, abscesses, lymphangiomatosis, xanthogranulomatous pyelonephritis, extramedullary hematopoiesis, retroperitoneal fibrosis and Erdheim-Chester disease. - Next, multimodality imaging characteristics of retroperitoneal masses will be demonstrated, including distinguishing water, enhancing tissue, hemorrhage and fat on MR, CT and US. The role of multiphasic MR and CT, as well as the potential role of dual energy CT, will be discussed. - The exhibit will subsequently review problem-solving tips in aiding diagnosis of retroperitoneal masses, with a collection of sample cases which will delineate methods to increase accuracy in diagnosis.

The anatomic complexity of the retroperitoneal space, as well as the wide spectrum of both benign and malignant pathology, make imaging interpretation of the retroperitoneal mass a diagnostic challenge. A knowledge of the normal and abnormal imaging patterns, an understanding of the complex anatomy, and an awareness of the unique imaging appearances in the differential of the retroperitoneal mass will allow the radiologist to provide more meaningful and accurate information essential in clinical management.