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Gastrointestinal Imaging

E2829. Rediscovering the Retroperitoneum: Masses and More

Sakala M,  Maturen K,  Shankar P,  Wasnik A. University of Michigan, Ann Arbor, MI

Address correspondence to M. Sakala (misakala@med.umich.edu)

Background Information: A variety of masses and mass-like processes can arise from the retroperitoneum. An understanding of retroperitoneal anatomy is key to make a differential diagnosis specific to the retroperitoneum. Some of the etiologic changes have overlapping features and others have a more classic appearance. This review will provide an image-guided approach to diagnosing retroperitoneal abnormalities.

Educational Goals/Teaching Points: The goals of this exhibit are to provide a brief anatomic review of the retroperitoneum and retroperitoneal spaces, illustrate the variety of masses and mass-like processes of the retroperitoneum using a multimodality image-guided approach, and emphasize distinctive imaging features of cases with overlapping features.

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques: A variety of masses and mass-like processes of the retroperitoneum will be discussed. These include lipomatosis, leiomyosarcoma, lymphoma, paraganglioma, extramedullary hematopoiesis, and endometriosis and uterine leiomyoma. Retroperitoneal lipomatosis is symmetric, benign proliferation of retroperitoneal fat whereas a well-differentiated liposarcoma is a mass of neoplastic proliferation of fat. Although fat is also present in dedifferentiated liposarcomas, soft tissue components are predominant. Leiomyosarcomas originate from smooth muscle outside of or within blood vessels (primarily the inferior vena cava [IVC]). Differentiation from other types of sarcomas can be challenging. The mass usually must be very large to cause vascular compromise. Lymphoma can present in a variety of forms including subtle soft tissue bulkiness, bulky lymph node enlargement with vascular encasement, and renal or perirenal extra-nodal spread. Vascular or ureteral compromise is less common with lymphoma compared with more plaque-like retroperitoneal fibrosis (primary or secondary). Other plaque-like processes include Erdheim-Chester disease, histiocytosis, or plasmacytomas. Paragangliomas most commonly occur in the abdomen and arise from the paraaortic sympathetic ganglia, especially the organ of Zuckerkandl. These may splay the IVC and aorta rather than involve vasculature like IVC leiomyosarcomas. Other tumors of neural origin can be identified by their perineural course and neuroforaminal expansion. Extramedullary hematopoiesis can appear as masses along and arising from osseous structures including the spine, sacrum, and pelvic bones. Endometriosis and uterine leiomyomas can also occur in the retroperitoneum.

Conclusion: A variety of retroperitoneal masses and mass-like processes have overlapping features and some have a classic imaging appearance. Knowledge of retroperitoneal anatomy and the spectrum of multimodality imaging features can assist in creating an astute differential diagnosis. In cases with nonspecific features, image-guided tissue sampling may be warranted for a definitive diagnosis.