腋窩に発生したhibernomaの一例

Abstract

This is a case report of a hibernoma arising from the axilla. The patient, a 54-year-old Japanese man, visited our hospital with the complaint of painless tumor in the left axilla. The size of the subcutaneous tumor was about 7 cm on palpation. On Magnetic Resonance Imaging (MRI), both T1-weighted and T2-weighted images of the tumor were homogenous high signal intensity, so we suspected lipoma. Subsequent MRI examination, however, revealed a non-fat part in the tumor. Because the tumor grew slowly, surgical therapy was performed to rule out malignancy. The resected tumor was 14 × 11 × 6cm in size and exhibited a greasy, brown cut surface. Histopathological examination revealed multivacuolated brown fat cells with granular cytoplasm and small, central nuclei intermixed with ordinary white fat cells. Although brown fat cells somewhat resemble lipoblasts, nuclei of brown fat cells are small, non-atypical and centrally located, and are characteristically distributed evenly through the tumor unrelated to blood vessels. Vasculatures are relatively abundant. No mitosis and atypical cells were detected. On immunohistochemical examination, brown fat cells showed cytoplasmic expression of S-100, and no nuclear expression of MDM2. A diagnosis of hibernoma was made. Correct pathological diagnosis is important to avoid an erroneous diagnosis of well-differentiated liposarcoma because "Lipoma-like" subtypes morphologi- cally bear a striking resemblance to well-differentiated liposarcoma, but hibernoma is a benign tumor that does not recur with complete local excision. MDM2 immunostaining is a useful adjunct in diagnosing well-differentiated liposarcoma. The patient has survived for 3 months since the operation, and shows good QOL under the follow-up.