ARRS 2022 Abstracts

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E1352. MR Imaging of Fat-Containing Soft Tissue Tumors: A Radiological Primer - Don’t Be Afraid of Those Few Extra Pounds!
Authors
  1. Shruti Kumar; University of Arkansas for Medical Sciences
  2. Gitanjali Bajaj; University of Arkansas for Medical Sciences
Background
Fat-containing tumors are the most common soft tissue tumors encountered in clinical practice, the majority of which are benign. Although characteristic imaging findings have been described for simple lipomas, there remains an overlap in imaging features between benign and malignant lipomatous tumors, posing diagnostic challenges for the radiologist. The purpose of this exhibit is to discuss the pertinent MRI features of lipomatous tumors and review the key differentiating features between benign adipocytic tumors and indeterminate/suspicious ones.

Educational Goals / Teaching Points
We wish to exhibit the imaging spectrum of fat-containing soft tissue tumors as per the WHO classification. Benign tumors include lipoma, lipoblastoma, myolipoma, chondroid lipoma, spindle cell lipoma, hibernoma, and lipomatosis. Intermediate tumors include well0differentiated liposarcoma (WDLPS)/atypical lipomatous tumor (ALT). Malignant tumors include dedifferentiated liposarcoma (DDLPS), myxoid liposarcoma, and pleomorphic liposarcoma. Other benign lipoma variants that may mimic the imaging appearance of WDLPS will also be discussed. We will also review the role of MDM2 gene amplification and MDM2 protein expression as a marker to differentiate between liposarcomas and lipomas.

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques
Most simple lipomas are superficial. Deep lipomatous lesions can be simple lipomas, lipoma variants, or well-differentiated liposarcomas. Because of differences in treatment, prognosis, and long-term follow-up, it is important to preoperatively distinguish simple lipomas from well-differentiated liposarcomas. Lipomas are well circumscribed, isointense to subcutaneous fat on all sequences, and show nonenhancing thin septations (< 2mm). Infiltration is often seen in deep lipomas. Lipoma variants can have variable appearance. WDLPS and ALT have thicker, irregular septations (> 2mm) with enhancement. They often mimic the imaging appearance of lipoma variants, hence warranting biopsy for histopathological confirmation. DDLPS have soft tissue nodules > 1 cm, with little to no macroscopic fat. Heterogeneity is often seen due to hemorrhage and necrosis.

Conclusion
Recognizing the spectrum of radiological appearances of fat-containing tumors distinguish the suspicious lesions from the benign ones, which has a direct bearing on disease prognosis and patient management.