E5515. Unrevealing the Enigma: A Pictorial Systematic Guide to Primary Retroperitoneal Neoplasms
  1. Samruddhi Jain; St. Vincent Hospital
  2. Mili Rohilla; St. Vincent Hospital
  3. Joshua Russell; St. Vincent Hospital
Primary retroperitoneal tumors are a heterogeneous group of rare lesions classified as primary when they do not originate from a specific retroperitoneal organ. The clinical findings are nonspecific and vary according to the behavior and location of the lesion (invasion of different organs). Most of the primary retroperitoneal tumors are malignant with a high mortality rate. These tumors are usually large at presentation owing to loose connective tissue in the retroperitoneum. The treatment is challenging because of the size of the lesion and vascular and retroperitoneal organ involvement.

Educational Goals / Teaching Points
Radiologic and anatomic correlation of anatomy of retroperitoneum. Describe and demonstrate the radiologic appearances of various primary retroperitoneal neoplasms. A systematic approach based on imaging characteristics for differentiating between differentials of retroperitoneal lesion.

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques
Classification of the retroperitoneal lesion is based on origin. 1. Adipocytic tumors, lipoma, liposarcoma. 2. Smooth muscle, leiomyoma, leiomyosarcoma. 3. Fibroblastic tumor, solitary fibrous tumor, fibrosarcoma. 4. Neurogenic tumor, neurofibroma and malignant peripheral nerve sheath tumor, schwannoma, ganglioneuroma, paraganglioma. 5. Miscellaneous soft tissue sarcoma, PEComas, germ cell tumors, desmoid, rhabdomyosarcomas, angiosarcoma, synovial cell sarcoma. Chondrosarcoma imaging: CT and MRI are the main imaging methods for diagnosis, biopsy, staging, and surgical planning. The absence of radiological signs – crescent sign, embedded organ sign, and phantom organ sign – can confirm the categorization of a mass as a primary retroperitoneal lesion. Though there is significant overlap in imaging findings and final diagnosis by histopathological analysis, the characteristic radiologic appearances provide clinical and surgical guidance.

CT and MRI play a paramount role in the diagnosis, evaluation, biopsy, and surgical planning of retroperitoneal neoplasm. As these tumors are usually large at presentation with overlapping imaging features, a systematic approach and knowledge of differentiating characteristics are critical for radiologists, as described in this pictorial review.