Lipoma Arborescence of Peroneal Tendon Sheath

Clinical History

A 29 year old male presented with history of intermittent pain and swelling along the lateral aspect of the left ankle over the past few months. No history of trauma or skin discoloration.

Imaging Findings

MRI showed a massive amount of fluid collection distending the peroneal tendon sheath. Multiple 'frond' like projections were noted along the wall of the tendon sheath which showed fat signal intensity. Mild enhancement was seen in the periphery of the tendon sheath on contrast images. No enhancement was noted in the 'fronds'. The tendon sheath also appeared thickened. No tear of the tendon was noted. Bones under review were normal.

Discussion

Lipoma arborescence or synovial lipomatosis is a rare entity that comprises less than 1% of all lipomatous lesions. It primarily affects the synovial lining of the joints and bursae with 'frond' like proliferation of the fatty tissue. The normal synovial tissue is replaced by hypertrophied villi which pathologically demonstrate mature lipocytes. There is coexistence of congested hyperemic capillaries and chronic inflammatory cells [1]. The synovial fluid is often free of cells and crystals [1]. Although lipoma arborescence is mostly found in elderly patients, it can be seen in the younger population. Occurrence in the settings of trauma, infection, osteoarthritis, collagen vascular disease and diabetes mellitus are reported [2]. It is the primary or idiopathic type which occurs more commonly in younger patients [2]. Patients present with long-standing and progressive swelling of the involved joint; which may be associated with pain, effusion and decreased range of movement [3]. Suprapatellar bursa above the knee joint is the commonest location. Less commonly affected joints include shoulder, hip and elbow joints. The involvement of the tendon sheath as in this case is rare. High frequency ultrasound confirms fluid collection and floating 'frond' like projections, which show wave like motion on dynamic compression [3]. The typical CT findings include a synovial lesion showing attenuation values in range of fat with absence of enhancement after intra-venous contrast and joint effusion. MRI shows thickening of the synovial lining and fluid collection distending the tendon sheath.The key finding includes the presence of fatty tissue in the form of 'frond' like projections along the wall of the tendon sheath which appear hyperintense on T1WI and show signal drop-out on fat suppressed sequence [4, 5]. When lipoma arborescence involves the joint, the adjoining bones may show erosions, which is more likely due to underlying arthritis rather than due to the disease itself. Lipoma arborescence is a benign condition with good prognosis after synovectomy. Recurrence is possible, especially if underlying factors such as chronic arthritis remain [5, 6]. In conclusion, lipoma arborescence is a rare lesion that needs to be considered in patients who have long-standing swelling and chronic effusion. MRI is a definitive tool in diagnosing and evaluating the extent of disease in most cases.

Differential Diagnosis List

Final Diagnosis

Lipoma arborescence of the peroneal tendon sheath

URL:	https://www.eurorad.org/case/13129
DOI:	10.1594/EURORAD/CASE.13129
ISSN:	1563-4086