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.
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.
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.
Lipoma arborescence of the peroneal tendon sheath
This work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License.
Based on MRI images, it is observed that in the lateral synovial sheath cavity of the patient's left ankle, there is patchy and lobulated fat-like signal thickening, presenting as “cluster-like” or “membranous” protrusions. On T1-weighted images, hyperintense signals can be seen, and in fat suppression sequences, these signals are markedly diminished (suppressed), indicative of a predominantly fatty composition. The lesion is clearly demarcated from the surrounding tissues, with no significant signs of bone cortical erosion or destruction. A small amount of fluid can be seen within the tendon sheath, and there is no obvious articular surface destruction or marked synovial enhancement. These imaging findings are consistent with “fatty synovial proliferation,” commonly referred to as Lipoma Arborescens.
Considering the patient’s age, symptoms (chronic pain and swelling), lack of significant trauma history, and MRI findings of distinct fatty component thickening and “cluster-like” synovial proliferation, the most likely diagnosis is Lipoma Arborescens.
For Lipoma Arborescens, the main treatment approaches include:
Rehabilitation / Exercise Prescription Recommendations:
Based on the “FITT-VP” principle, during the postoperative period following synovectomy or in phases when symptoms have subsided, an individualized, gradual rehabilitation program is recommended:
If the patient has other comorbidities (e.g., arthritis, metabolic diseases), it is recommended to develop an individualized training plan under the guidance of a specialist or rehabilitation therapist, with regular monitoring of joint health as needed.
Disclaimer: This report is provided based on the given imaging and clinical information for comprehensive analysis and reference. It should not replace an in-person consultation or professional medical advice. Please consult a specialist to develop a clinical treatment plan that considers the patient's specific circumstances.
Lipoma arborescence of the peroneal tendon sheath
