Imaging of hibernomas: A retrospective study on twelve cases.

Background: To analyze the imaging features of hibernomas on computed tomography (CT) and magnetic resonance (MRI).

Methods: Twelve hibernomas were retrospectively assessed with CT and MR imaging and compared to the histology of the specimen

Results: Nine females and three males with a mean age of 30 years were included. Ten tumors occurred in the thigh and two affected the subcutis of the periscapular and buttock regions. On eight CT scans, seven (87,5%) lesions were homogeneous and mildly to moderately hyperdense compared to subcutaneous fat while one lesion was heterogeneous with mixed hypo and hyperattenuating areas. On six T1W images, five (83,3%) lesions appeared homogeneous and hypointense relative to subcutaneous fat and one was heterogeneous. Incomplete fat suppression was depicted in all cases. All lesions displayed marked enhancement. Large intratumoral vessels were depicted in three of the 12 (25%) cases. Septations were depicted on four of the eight unenhanced CT and on all six MRI examinations.

Conclusions: Hibernoma usually appears hypodense and hypointense relative to subcutaneous fat on pre-contrast CT and MR T1W with variable enhancement patterns and incomplete fat suppression on STIR or fat-saturated sequences. These characteristics relate directly to the presence of brown fat. However, atypical findings such as heterogeneous patterns of mixed fatty and non fatty components on unenhanced CT and MR T1W can be also encountered. Absence of large intratumoral vessels should not exclude hibernomas from the differential diagnosis of regional lipomatous tumors.