Synovial Lipomatosis of Ankle with Sural Nerve Neuropathy: A Rare Case Report

ABSTRACT: Synovial lipomatosis, also known as lipoma arborescens, is a rare benign condition characterized by villous fatty proliferation of the synovium with replacement of the subsynovial tissue by mature adipocytes. Although it predominantly affects the knee joint, involvement of the ankle is distinctly uncommon. We report the case of a 52-year-old woman who presented with progressive left ankle pain and swelling of 1 year duration, associated with mechanical symptoms and restriction of motion. Physical examination revealed a posterolateral ankle swelling with mild limitation of range of motion, while laboratory parameters and rheumatologic markers were within normal limits. Plain radiography demonstrated a soft-tissue swelling with a calcified/bony mass, and magnetic resonance imaging revealed diffuse synovial proliferation with associated bone marrow edema. The patient underwent open ankle arthrotomy with excision of a loose calcified body and synovectomy. Histopathological examination confirmed synovial lipomatosis, showing fibrocollagenous tissue lined by hyperplastic synovial membrane with infiltration of mature adipocytes in a myxoid stroma, without evidence of malignancy. Postoperatively, the patient achieved complete symptomatic relief with restoration of normal ankle function at 6 months of follow-up, and no recurrence was noted at 1 year. This case highlights synovial lipomatosis as an important differential diagnosis for chronic ankle swelling and supports surgical synovectomy as an effective treatment with excellent clinical outcome and low recurrence.