Introduction. A hibernoma is a rare benign tumor derived from vestigial remnants of brown adipose tissue. In neonates this tissue makes up about 5% of the body mass and its amount greatly decreases after birth, persisting only in scattered subcutaneous areas. In rare cases, brown fat continues to grow leading to a hibernoma that may be located in the head and neck. We present an illustrative case of a large hibernoma of the neck with infraclavicular extension and discuss about diagnostic and treatment difficulties. Case report. A 29-year-old male presented with large, slowly progressive, painless neck mass that was noticed 6 months earlier. Computed tomography (CT) and magnetic resonance (MR) showed a well-vascularized, soft tissue tumor of the lateral region of the neck and supraclavicular fossa with extension below clavicle. Treatment included arterial embolization followed by challenging surgical removal of the tumor. Dissection was performed at III, IV and V levels of the neck, making complete resection possible without the tumor fragmentation or major blood vessels and cranial nerves injuries. The final diagnosis of the hibernoma was made by histopathological analysis. The patient had no signs of recurrence during three-year follow-up. Conclusion. Although the CT scan and MR may raise the suspicion, hibernoma is definitely diagnosed by a pathologist. It is very important to exclude the malignant processes, foremost liposarcoma. The tumor fragmentation during surgery should be avoided because the high vascularity of the tumor tissue carries a substantial risk for hemorrhage. Our experience with preoperative embolization and complete tumor resection in this case showed positive impact on the final outcome.
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