Kidney hibernoma: case report and literature review

Hibernomas are rare benign tumours originating from the brown adipose tissue. They occur generally in adults with a peak incidence in the third decade and with a slightly predominance in women. They are benign tumor that does not recur with complete excision. CT and RM images should not be misdiagnosed with atypical lipomas or well-differentiated liposarcoma. We report a case of incidental renal hibernoma discovered in a 51 years old women during open surgery for kidney pielic stone.

A 51-year-old woman presenting with recurrent left flank pain was diagnosed with left kidney stone. Abdomen ultrasound and i.v. pyelografy showed pyelic stone of 2 cm without other pathologies of the urinary tract. Patient underwent left percutaneus lithitripsy complicated by severe bleeding. We converted into open surgery and incidentally we observed a brown, well-defined, encapsulated, and mobile mass of 1 cm that resulted to adhere to kidney capsule. We removed this lesion respecting surgical borders. Intraoperative histological examination revealed cells with eosinofil cytoplasm and no evidence of mitosis or cellular atypia. Definitive histological examination show a well-circumscribed, encapsulated tumor, with large cells with central nuclei and multivacuolated granular cytoplasm. A rich vascular network was present absence of mitosis or atypia was confirmed. Histological diagnosis presumed hibernoma.

Our case report results one of the few cases of renal localisation of hibernoma that however need a surgical treatment.