E2129. An Approach to Retroperitoneal Pathology
  1. May Lim; Singapore General Hospital
  2. Elizabeth Cheong; Singapore General Hospital
Retroperitoneal pathologies originate from the soft tissues, lymphatics or neural tissues of the retroperitoneum. They may be neoplastic or nonneoplastic, and may be categorised as benign or malignant. Imaging often plays a key role in narrowing down the differential diagnoses of these pathologies, thereby guiding further management. We review the various neoplastic and nonneoplastic pathologies that occur in the retroperitoneum, and discuss key imaging features that can aid in differentiating between the different pathologies.

Educational Goals / Teaching Points
Review the anatomy of the retroperitoneum, and to discuss imaging features that confirm retroperitoneal origin of the pathology. At the end of the exhibit, we hope the reader will be able to discuss the differential diagnosis for neoplastic and nonneoplastic pathologies occurring in the retroperitoneum, as well as their characteristic imaging features.

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques
The retroperitoneum comprises three compartments: the anterior pararenal space, the perirenal space, and the posterior pararenal space. The anterior and posterior pararenal spaces merge inferiorly to form an infrarenal retroperitoneal space, which in turn communicates inferiorly with the prevesical space and extraperitoneal compartments of the pelvis. Primary retroperitoneal pathology should be confirmed by excluding origin from a retroperitoneal organ. Instead, retroperitoneal pathology should cause anterior displacement of the retroperitoneal organs, such as the kidneys, adrenal glands, pancreas, and ascending and descending colon. Primary retroperitoneal neoplasms include mesenchymal tumours (such as lipoma and liposarcoma), lymphomas, neurogenic tumours and germ cell origin tumours. Primary nonneoplastic retroperitoneal conditions include retroperitoneal hemorrhage, abscess, arteriovenous malformation, retroperitoneal fibrosis and Castleman’s disease. Overall, neoplastic processes present with mass-like appearances, and are often associated with adjacent organ displacement. On the contrary, nonmalignant processes usually present with ill-defined, infiltrative and non-mass-like appearance, surrounding and encasing adjacent anatomical structures. Determining the composition of the mass on Computed Tomography (CT) and Magnetic Resonance (MR) imaging can further aid in diagnosis, for instance the identification of fat, myxoid, cystic or necrotic components.

There is a diverse range of retroperitoneal pathologies arising distinct from the retroperitoneal organs. Good knowledge of these pathologies and attention to unique imaging features will aid in narrowing down the differentials.