Saudi Journal of Sports Medicine

: 2016  |  Volume : 16  |  Issue : 2  |  Page : 147--149

Bilateral knee lipoma arborescens: A case report and review of literature

Atul Mahajan 
 Department of Orthopedics, Lady Hardinge Medical College, New Delhi, India

Correspondence Address:
Dr. Atul Mahajan
G-22, Bali Nagar, New Delhi - 110 015


Lipoma arborescens (LA) is a rare disorder characterized by villous lipomatous proliferation of the synovial tissue. Magnetic resonance imaging is the investigation of choice, with images clearest on fat-suppressed or STIR sequences. Synovectomy appears to be curative. We present a case of bilateral LA of knees and undertake a comprehensive review of the literature.

How to cite this article:
Mahajan A. Bilateral knee lipoma arborescens: A case report and review of literature.Saudi J Sports Med 2016;16:147-149

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Mahajan A. Bilateral knee lipoma arborescens: A case report and review of literature. Saudi J Sports Med [serial online] 2016 [cited 2022 Oct 3 ];16:147-149
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Lipoma arborescens (LA) is a rare disorder characterized by villous lipomatous proliferation of the synovial tissue. This condition is more common in men than in women, and most affected patients are in the fifth to sixth decades of life. It is usually monoarticular, occurring most frequently in the knee, particularly in the suprapatellar pouch. [1],[2] Magnetic resonance imaging (MRI) is the investigation of choice and synovectomy appears to be curative. [3] We present a case of bilateral LA of knees and undertake a comprehensive review of the literature.

 Case Report

A 45-year-old male patient presented with a 3-year history of bilateral knee pain and swelling (right > left). The pain and swelling were spontaneous in onset and there was no documented history of an associated injury. The pain and swelling had gradually worsened. There were no signs of mechanical obstruction in the knee. On examination, the patient was systematically well. He had bilateral swellings of the knees, with suprapatellar pouch showing boggy swellings in both the knees. He was able to flex up to 100°. There was medial joint line tenderness on palpation, crepitus, effusion, and thickened synovium mainly in the suprapatellar region.

Imaging findings

Initial radiographs of the bilateral knees demonstrated exuberant osteophytes from articular margins of tibiofemoral and patella femoral joints. The medial tibiofemoral joint spaces were reduced [Figure 1]. Findings were suggestive of severe osteoarthritis bilateral knees.{Figure 1}

MRI revealed extensive synovial abnormality in bilateral knees. Both knees revealed diffuse, villous hypertrophy of the synovium in frond-like pattern involving anterior and posterior joint spaces and suprapatellar bursal region [Figure 2]. Postcontrast scan showed peripheral enhancement of villous synovium. There was associated moderate synovial knee joint and suprapatellar bursal effusion. The patient underwent arthroscopic synovectomy of the right knee. During surgery, extensive frond-like fatty proliferation was noted throughout the joint [Figure 3]. Histologic analysis revealed elongated synovial folds distended by mature fat cells without atypia or malignancy [Figure 4]. A dense and focally nodular lymphocytic and plasmacellular infiltrate was seen in the synovium, which, along with fatty proliferation, was evidence of coexistent chronic synovitis. Approximately 2 weeks later, the patient underwent arthroscopic synovectomy of the left knee. The left knee also revealed similar findings to the right knee.{Figure 2}{Figure 3}{Figure 4}


LA is characterized by prominent villous proliferation in the synovium and extensive replacement of the subsynovial tissue by mature adipose cells. It was first described by Hoffa according to whom frond-like appearance resembled a tree in leaf; hence, the Latin term Arborescens ("treeforming" or "treelike"). It can be mono-, bi-, or poly-articular and can affect patients of all ages (although it is most common in the fifth decade and above). Most commonly, the knee joint is involved. But the condition has also been described in wrist, shoulder, elbow, ankle and hip joints. Associated conditions have included osteoarthritis, [4] joint trauma, and diabetes mellitus; [4] in 20% of the cases, popliteal cysts are noted. [4]

Affected patients usually report a long-standing, slowly progressive swelling of the joint with recurrent effusions, and variable pain and limitation of motion. [1],[2] There is a soft, painful, boggy swelling in the suprapatellar pouch, and laboratory tests are usually normal. Plain radiographs may show tissue density in the suprapatellar pouch.

LA appears to predispose to osteoarthritis although the cause for this is unknown. One theory suggests that chronic irritation of the synovium and underlying cartilage by the synovial fronds and long-standing effusions leads to degenerative changes. [5] The severity of the osteoarthritic changes in the affected knees has been suggested to correlate with the duration of the symptoms. Morphologically distinct subtypes of LA exist in patients with and without a history of pre-existing inflammatory joint disease. Subtypes with previously normal joints demonstrated synovial fronds alone while the more typical villonodular picture is found in patients with a preceding history of joint disease.

It has been suggested that an inverse relationship exists between adipocyte differentiation and the osteogenic activity of bone marrow stromal cells, and that this is reciprocally regulated by bone morphogenetic proteins. According to Ikushima et al., [5] LA is a rare form of a reactive lesion of the synovium in which the mesenchymal stem cells differentiate into adipocytes, whereas osteochondral differentiation of the mesenchymal stem cells results in synovial chondromatosis. They therefore suggested that LA and synovial chondromatosis might have a common etiology. Three patterns of LA are identified as per MRI imaging, the most common of which is a diffuse villous proliferation, although a discrete mass lesion and a mixed pattern can also be observed. The appearance on MRI is diagnostic and includes a synovial mass with a frond-like architecture and a fat-signal intensity on all pulse sequences, which is suppressed using fat-selective presaturation, mass-like subsynovial fat deposit, joint effusion, potential chemical shift artifacts at the interface of the synovial lesion and the effusion, and no evidence of hemosiderin deposition. [6],[7] Macroscopically, LA has a frond-like appearance with numerous broad-based polypoid or thin papillary villi composed of fatty, yellow tissue. Histologically, the villi are filled with mature adipose cells. The overlying synovial membrane may contain mononuclear chronic inflammatory cells and the synovial cells may appear to be enlarged and reactive, with abundant eosinophilic cytoplasm.

The differential diagnosis includes pigmented villonodular synovitis, synovial lipoma, synovial chondromatosis, rheumatoid arthritis, synovial hemangioma, amyloid arthropathy, and xanthomata. Pigmented villonodular synovitis has a low intensity on T1- and T2-weighted images due to hemosiderin accumulation; rheumatoid arthritis can be differentiated from LA by the intermediate signal on T1-weighted and the decreased signal on T2-weighted images. Synovial chondromatosis and hemangiomas show low to intermediate signal intensities on T1- and T2-weighted images. The treatment for LA is open or arthroscopic arthrotomy and synovectomy. Arthroscopic synovectomy can be performed in cases of LA when the proliferation is less extensive and confined to the anterior knee compartment. Arthroscopy reduces soft-tissue trauma and helps in postoperative rehabilitation. In extensive lesions, open synovectomy is suggested. [8] Synovectomy has been reported to result in complete and long-standing alleviation of symptoms of LA in most patients but does not appear to halt the progression of secondary osteoarthritis. Nonsurgical alternatives to synovectomy appear to be successful. Erselcan et al. [9] successfully used yttrium 90 radiosynovectomy to treat and chemical synovectomy with osmic acid has also been described.

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Conflicts of interest

There are no conflicts of interest.


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