Atypical lipomatous tumor - thigh
Investigation of increased radiotracer uptake in right thigh. History of metastatic prostate carcinoma.
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Heterogeneous infiltration, predominantly of fat signal and without sharp borders, at the posterior aspect of the right thigh in the area of the intermuscular septum. It measures approximately 12 cm in length, widens the septum and at its distal end appears as a well-defined structure measuring 2.8 cm in diameter. It contains intermediate-signal septae that enhance after contrast injection, along with peripheral enhancement. The sciatic nerve traverses the structure.
The greater trochanters show irregular borders and post-contrast enhancement, compatible with tendinosis.
The fatty process in the right thigh was determined to be an atypical lipomatous tumor rather than a lipoma due to the aforementioned characteristics. "Atypical lipomatous tumor" is used interchangeably with "well-differentiated liposarcoma" and is preferred to the latter in cases where the lesion is in an extermity (i.e. accessible and surgically removable) 1. In this case, though, due to sciatic nerve involvement, follow-up MRI in 3 months was recommended.