Differentiation of Atypical Lipomatous Tumors from Lipomas: Our Experience with Visual Analysis of Conventional...

Differentiating atypical lipomatous tumors (ALTs) from lipomas using imaging techniques is a challenge, and the biopsy with immunohistochemical determination of murine double minute 2 (MDM2) oncogene is the gold standard. We are looking for a management algorithm with the visual analysis of magnetic resonance images in these two fatty soft tissue tumors that allow us to avoid some biopsies. Two radiologists, blinded to the final diagnosis, independently assessed various features on conventional magnetic resonance imaging (MRI), in 79 patients with pathologically confirmed fatty tumors as either lipoma (MDM2 negative) or ALT (MDM2 positive). Results: The interobserver agreement for the most MRI features was moderate and the musculoskeletal radiologist accuracy for final diagnosis was 90% sensitivity and 66% specificity. Tumors with homogeneous fat signals and a maximum size < 8 cm were always lipomas (p < 0.001), and the tumors with septa thickness ≥ 2 mm, or more than one non-fat nodule, and a maximum size ≥ 12.8 cm were typically ALTs. While those tumors with septa < 2 mm or one non-fat nodule, independently of maximum size, the diagnosis of lipoma versus ALT is uncertain and a biopsy is required.