The patient presented with a 6-month history of pain and swelling of the right knee.
The patient presented with a 6-month history of pain and swelling of the right knee.
An MR examination was performed. The study showed an extensive synovial proliferation in the suprapatellar bursa. The lesion had a frond-like villous apperance and was isointense to fat in all sequences (Figs 1-5). The lesion extended to both suprapatellar compartments of the knee joint.
These findings were compatible with a diagnosis of lipoma arborescens. A synovectomy was performed through a medial parapattelar arthrotomy. Histological examination revealed synovial tissue almost replaced by mature fat cells (Fig. 6). The diagnosis was lipoma arborescens.
Lipoma arborescens is a rare benign intrarticular lesion characterised by the replacement of the subsynovial tissue by mature fat cells giving rise to a villous proliferation. It usually involves the suprapatellar pouch of the knee joint (1-5), although it has also been described in other locations including the shoulder, subdeltoid bursa, hip, elbow, hand and ankle (3). Bilateral involvement of the knees, wrists, ankles and hips and involvement of multiple joints has also been observed (1). Clinically the most common finding is a slow increase in painless swelling, accompanied by intermittent effusion of the joint. Most affected patients are in the fifth to seventh decades of life.
Lipoma arborescens can be similar to other proliferations of the synovial membrane, but the characteristic feature is macroscopic hypertrophic lipomatous synovial tissue. The term arborescens, from the Latin word arbor meaning tree, defines the characteristic morphology of this lipomatous villous synovial proliferation, i.e. resembling a tree in appearance.
Magnetic resonance imaging (MRI) appearances of lipoma arborescens correspond and correlate with the fatty proliferation of the synovial lesion, which allows a specific diagnosis to be made. MRI is better at characterising soft tissue than other radiological techniques, and also fat suppressed sequences or STIR sequences can be obtained (Figs 2,4). For this reason the histological appearance of lipoma arborescens within the synovial tissue can be perfectly correlated on MRI.
Lipoma arborescens must be differentiated from other synovial lesions. The differential diagnosis should include other diffuse pathology of the synovium: villonodular pigmented synovitis, synovial chondromatosis, synovial haemangioma and rheumatoid arthritis.
Villonodular pigmented synovitis typically shows a diffuse low signal associated with haemosiderin. Synovial chondromatosis shows an intermediate-low signal on T1- and T2-weighted images, related to the cartilagenous nature of the lesion. Synovial haemangiomas show intermediate signal intensity on T1- and T2-weighted images with areas of low signal intensity due to phleboliths or fluid void within a linear punctate lesion of high signal intensity corresponding to fibrous fatty septa between the vascular channels. Chronic rheumatoid arthritis shows intermediate-low signal on T1- and T2-weighted images associated with the formation of fibrous pannus.
It has been suggested that there is an association with osteoarthritis, rheumatoid arthritis or trauma (5), but the exact aetiology of lipoma arborescens remains unknown.
Lipoma arborescens
Based on the patient's right knee MRI, the joint synovium shows significant villous hyperplasia with fat signal (high signal) on T1-weighted images. The lesion primarily affects the suprapatellar bursa area and surrounding synovial tissue, presenting a tree-like (arborescent) proliferation, with relatively well-defined boundaries. Localized joint effusion is visible in the articular cavity, and there is no obvious bone erosion or compressive destruction. No significant pathological swelling is noted in the surrounding soft tissues.
1. Lipoma arborescens: Given the villous synovial proliferation with prominent fat signal and a tree-like distribution, this is the primary consideration. It is commonly seen in the knee joint, with clinical manifestations often including chronic painless or mildly painful joint swelling.
2. Pigmented Villonodular Synovitis (PVNS): Typically appears as low signal intensity on T2-weighted images due to hemosiderin deposition within the synovium, which differs from this case. However, it remains in the differential diagnosis.
3. Synovial Chondromatosis: Characterized by chondroid nodules proliferating from the joint synovium. On T1- and T2-weighted images, it usually shows low to intermediate signal intensity, often with calcifications, which is not in line with the prominent fat signal found in this case.
4. Synovial Hemangioma: MRI findings typically show high signal intensity characteristic of vascular tumors, with fibrous septa and flow voids. Since this case is dominated by fat signal, hemangioma is less likely.
5. Rheumatoid Arthritis (RA): Commonly presents with synovial thickening and symmetrical involvement of multiple joints, often accompanied by positive laboratory findings such as rheumatoid factor or anti-CCP antibodies. The imaging findings here suggest lipomatous rather than inflammatory changes in the synovium.
Considering the patient’s age, clinical symptoms, a 6-month history of chronic joint swelling, and classic “tree-like” fat-proliferating synovium on MRI, the most likely diagnosis is Lipoma arborescens.
1. Conservative Treatment: In mild cases, initial management may include joint immobilization, physical therapy, oral non-steroidal anti-inflammatory drugs (NSAIDs) to reduce discomfort and inflammation, along with muscle-strengthening exercises to stabilize the knee joint. Intra-articular injections (e.g., hyaluronic acid) can help decrease friction and improve symptoms.
2. Indications for Surgical Treatment: Patients with significant symptoms or those unresponsive to conservative management may consider arthroscopic or open synovectomy. Arthroscopic surgery can aim to completely remove the affected synovium to alleviate swelling and pain.
3. Rehabilitation/Exercise Prescription Recommendations:
The entire rehabilitation process should follow FITT-VP principles (Frequency, Intensity, Time, Type, Volume, and Progression) and be strictly individualized. If significant pain, swelling, or any discomfort arises during exercise, please consult a physician or rehabilitation therapist promptly.
This report is a reference analysis based on current imaging and medical history information. It does not replace an in-person diagnosis or professional medical advice. If the patient experiences any new symptoms or has concerns regarding the diagnosis or treatment plan, it is recommended to seek further evaluation and treatment at a qualified medical institution.
Lipoma arborescens
