Article

Clinical findings of hibernoma of the buttock and thigh: rare involvements and extremely high uptake of FDG-PET.

Department of Orthopedic Surgery, School of Medicine, Iwate Medical University, Morioka, Japan.
Medical science monitor: international medical journal of experimental and clinical research (Impact Factor: 1.22). 08/2009; 15(7):CS117-22.
Source: PubMed

ABSTRACT Hibernoma is a rare adipose tissue tumor of the soft tissue and the term is derived from the histological similarities to the brown fat found in hibernating animals. It usually occurs in the interscapular area, back, and neck and a few cases have been reported in the buttock or thigh.
Two cases are presented, one of which had a lesion in the buttock and the other a lesion in the thigh. The lesion in the buttock extended into the pelvis. CT and MR findings suggested liposarcoma in both cases, but the uptake was extremely intense on 18F-FDG-PET in one case. This was not typical of liposarcoma and suggestive of hibernoma. Biopsy specimens revealed a proliferation of adipose cells with vacuolated granular eosinophilic cytoplasm. No cellular atypia or mitotic figures were observed in either case. A marginal excision was performed in one case and an intralesional excision in the other. There were no signs of local recurrence at the final follow-up.
While occurrences in the buttock or thigh are exceedingly rare, hibernoma should be included in the differential diagnosis of an adipose tissue tumor in the thigh, even though the imaging findings mimic liposarcoma. 18F-FDG-PET may be a very meaningful technique to differentiate hibernoma from liposarcoma. A correct diagnosis should be established to prevent over-surgery.

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    ABSTRACT: We present a glucose avid hibernoma hampering the re-staging of advanced breast cancer with FDG PET and summa- rize the results of the available literature. FDG PET, CT, MRI, ultrasound and histology were performed according to standardized protocols in our case. The literature search was performed on PubMed.gov. The literature search revealed 29 relevant publications starting with 2002. The high metabolic activity of hibernomas is a precarious pitfall in the staging of patients with a high pretest probability of malignancy and an increasing number of published cases indicate a possibly underestimated problem necessitating histological work-up in most cases. In our experience and in accordance with the literature unusually high uptake of a lesion and fat equivalent density in the CT should raise the suspicion for a hibernoma. The differential diagnosis between hibernomas and liposarcoma is often impossible without biopsy and his-tological work-up to prevent unnecessary treatment.
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