What is in the differential diagnosis for this mass?
The mass is hypoattenuating and appears to contain fat, but it has more complexity and vascularity than a lipoma. A soft tissue sarcoma, such as liposarcoma, or a brown fat tumor (hibernoma) are on the differential.
There is a relatively well-marginated mass between the right gluteus maximus and gluteus medius muscles. The attenuation of the mass is between fat and muscle and there is a prominent vessel entering the mass at the lateral margin.