Intermuscular Hibernoma of the Thigh: A Diagnostic and Surgical Challenge Managed With Preoperative Embolization

This report describes a rare case of a large intermuscular hibernoma of the thigh associated with an intralesional arteriovenous malformation (AVM), presented to highlight the diagnostic challenges and the role of preoperative embolization in facilitating safe surgical excision. A 50-year-old female presented with a painless, progressively enlarging swelling over the anterior aspect of the left thigh for one year. On examination, a firm, non-tender, slightly mobile mass measuring approximately 20 × 15 cm was noted in the intermuscular plane, with intact neurovascular function. MRI revealed a well-defined fatty lesion with multiple tortuous vascular flow voids, hyperintense on T1 and heterogeneously hyperintense on T2/STIR, with heterogeneous post-contrast enhancement. CT angiography demonstrated multiple feeding vessels arising from the lateral branch of the profunda femoris artery and an intra-lesional AVM. Selective embolization of the feeding vessels was performed preoperatively to reduce intraoperative blood loss. Surgical excision under spinal anesthesia revealed a well-encapsulated, highly vascular mass situated between the sartorius and rectus femoris/vastus muscles, which was removed en bloc with minimal bleeding. Histopathology showed multivacuolated adipocytes with granular cytoplasm and central nuclei, without atypia, confirming a benign hibernoma. The postoperative period was uneventful, and no recurrence was observed at follow-up.