Intraosseous hibernoma.

We describe the imaging and pathological features of a rare case of sacral hibernoma that was discovered incidentally in a patient with low back pain. The benign-appearing, small intraosseous lesion in the sacrum was sclerotic on CT. MRI revealed that the lesion was heterogeneously hyperintense on T1W (lower in intensity than subcutaneous fat) and heterogeneously hypointense on fat-saturated T2W and STIR images. It showed mild heterogeneous enhancement on the post-contrast fat-saturated T1 MR images due to increased vascularity. A biopsy of the lesion was performed. The biopsy specimen demonstrated multivacuolated cells with immunohistochemical features of brown adipose tissue consistent with hibernoma.