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The aim of this study was to evaluate observer performance using T1-weighted spin-echo and fluid-sensitive MRI sequences in distinguishing between lipoma and atypical lipomatous tumour/well-differentiated liposarcoma (ALT/WDL). Magnetic resonance images of 51 patients with benign lipoma and ALT/WDL of the musculoskeletal system were reviewed. There were 33 benign lipomas and 18 ALT/WDL. The character of septa and nodularity of the fatty tumours on T1-weighted spin-echo sequences and the presence of high signal on fluid-sensitive sequences were assessed. Two independent observers took part. Observer agreement was measured. The two observers achieved sensitivities of 100 and 94% for T1-weighted images and 100% each for fluid-sensitive sequences. Specificities were 76 and 64% for T1-weighted and 70 and 73% for fluid-sensitive images. Observer agreement was very good (kappa 0.87 for T1-weighted and 0.88 for fluid-sensitive images). In distinguishing lipoma from ALT/WDL, observer performance was comparable using T1-weighted and fluid-sensitive MR sequences. High sensitivity and moderately high specificity were attained.

Lipoma arborescens is rare and usually found in the knee. We report two cases in the bicipital bursa of the elbow that showed characteristic findings on magnetic resonance imaging with contrast enhancement.