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October 2004 Case of the Month |
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Compiled by: Roel Galope, DO
Clinical Information: 50 year old female with knee effusion for the past 5 years.
MRI of the Left Knee:
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Findings:
Images reveal numerous hypertrophied synovial villous projections with signal characteristics identical to subcutaneous fat (isointense to fat on T1 and T2, suppresses on STIR). A knee effusion distends the suprapatellar recess. Osteoarthritis of the patellofemoral joint is demonstrated with patellar spurs and prominent erosions of the femoral trochlea. A medial meniscus tear was also present (not shown).
Diagnosis:
Lipoma Arborescens (Villous Lipomatous Proliferation of the Synovial Membrane)
Discussion:
Lipoma arborescens is a rare intraarticular lesion. Usually found in the suprapatellar recess of the knee joint, it has also been reported in other joints including the wrist, shoulder, elbow and hip. It is more common in men than women, usually in the fifth to seventh decades. Bilateral involvement has been observed.
Patients can be asymptomatic, but usually present with a complaint of slow increase in painless swelling, accompanied by recurrent joint effusion. As the effusion increases, pain and limited range of motion can develop.
The lesion is characterized by replacement of subsynovial tissue by mature fat cells, giving rise to an arborescent (tree-like) villous proliferation. Although its true etiology is unknown, it is thought to represent a reactive process to chronic irritation of the synovial membrane from inflammatory (rheumatoid arthritis), traumatic (meniscal tears), or degenerative joint disease. Exacerbation of effusion is thought secondary to impingement of proliferative villi at the patellofemoral or femorotibial joints.
Aspirated fluid is usually clear and yellow, but one case of hemarthrosis has been reported.
Preoperative diagnosis is usually through MRI which reveals masslike subsynovial fat deposition (38%), joint effusion (100%), erosive bone changes at articular margins (38%), associated synovial cysts (25%), and degenerative changes (13%).
Main differential considerations for synovial lesions in the knee include, diffuse or focal villonodular synovitis, diffuse or focal pigmented villonodular synovitis, primary synovial chondromatosis, and lipoma arborescens. The table below reveals the differences in MRI findings for these lesions.
MR Characteristics of Synovial Lesions
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Diffuse or focal villonodular synovitis
Villous or lobulated masses
Intermediate T1
Intermediate-hyperintense T2
Enhancement
Tends to extend into the semimenbranosus-gastrocnemius bursa
Effusion
Capsulosynovial thickening |
Diffuse or focal pigmented villonodular synovitis
Villous or lobulated masses
Hemosiderin
Hypointense T1
Intermediate-hypointense T2
Enhancement
Tends to extend into the semimenbranosus-gastrocnemius bursa
Effusion
Capsulosynovial thickening |
Primary synovial chondromatosis
Well-defined rounded masses
Loose body signal
Hypointense T1
Intermediate-hypointense T2
No enhancement
Loose bodies can be found within decompressed cysts
Effusion
Capsulosynovial thickening |
Lipoma arborescens
Villous or lobulated masses
Fat signal
Uniform hyperintense T1
Intermediate-hypointense T2
No enhancement
Suprapatellar bursa
Effusion
Capsulosynovial thickening |
Adapted from Gamuts and Pearls in MRI & Orthopedics, Pomeranz 1997
The recommended treatment for this condition is complete synovectomy, performed as an open procedure. There is only one documented report of recurrence. Less extensive lesions can be treated arthroscopically. Succesful treatment of lipoma arborescens with Yttrium-90 radiosynovectomy has also been reported.
References:
Chung CH et al, Intra-Articular Lipoma Arborescens of the Knee Joint. J Med Sci. 2004; 24(4):223-226.
Erselcan T, et al, Lipoma Arborescens; Successfully Treated by Yttrium-90 Radiosynovectomy. Annals of Nuclear Medicine. 2003; 17(7), 593-596.
Ryu KN, Jaovisidha S, Schweitzer M, Motta AO and Resnick D, MR Imaging of Lipoma Arborescens of the Knee Joint. American Journal of Roentgenology, Vol 167, 1229-1232
Vilanova JC et al. Lipoma Arborescens of the Knee. http://www.eurorad.org/case.cfm?uid=1935
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