Lipoma Arborescens: A Rare Synovial Lesion Unveiled by Radiologic Imaging

Lipoma arborescens (LA) is a rare benign synovial lesion characterized by villous proliferation of mature adipose tissue within the joint lining, most commonly affecting the knee. It is often linked to chronic irritation or inflammation of the synovium. A 46-year-old male presented with dull aching pain, intermittent swelling and a clicking sensation in his left knee for 3 years. Clinical examination revealed a soft suprapatellar swelling without redness, warmth or tenderness and a full range of motion with mild discomfort. Radiographs showed soft tissue swelling, while computed tomography demonstrated intra-articular fat-attenuating lesions. Magnetic resonance imaging (MRI) revealed characteristic frond-like fatty projections arising from the synovial lining, hyperintense on T1-weighted images and suppressed on fat-saturated sequences, consistent with LA. The patient underwent open synovectomy and histopathology confirmed villous proliferation of synovium with mature adipocytes. Postoperative recovery was uneventful and symptoms resolved completely. LA should be suspected in cases of chronic painless joint swelling with effusion and fatty synovial proliferation on imaging. MRI serves as the gold standard for diagnosis and differentiation from conditions like pigmented villonodular synovitis or synovial chondromatosis. Synovectomy remains the treatment of choice, offering excellent outcomes and low recurrence when the lesion is completely excised.