Working Diagnosis:
Lipoma Arborescens

Treatment:
US guided drainage of fluid was performed in the suprapatellar region and more than 75 ml of bloody fluid was removed. It was followed by a corticosteroid injection and the knee was wrapped in an ACE bandage.

Outcome:
Patient returned in 4 weeks with marked improvement in his knee joint movement and discomfort including walking and climbing stairs. He also started knee strengthening exercises and was advised to return to the office for any issues.

Author's Comments:
Lipoma arborescens is a slowly progressive intra-articular knee predominant lesion characterized by diffuse lipomatous villous transformation of the synovium. It is diagnosed by characteristic features on various imaging modalities including MRI. These findings include a fat-containing frond-like synovial mass, usually outlined by concurrent joint effusion. Although it is rare, it should be included in the differential diagnosis of chronic knee swelling or hemarthroses. Initial management of symptomatic lesions include aspiration and steroid injection. For persistent swelling synovectomy is indicated.

Editor's Comments:
Knee effusions require an extensive differential diagnosis. Male patients in the third to fifth decade of life with mechanical symptoms should have a lipoma arborescens considered. MRI is the imaging modality of choice when contemplating this diagnosis. As stated by the authors initial treatment may include arthrocentesis followed by a steroid injection, however, in refractory cases arthroscopic synovectomy may be required.

References:
1. Hallel T, Lew Basil M. Villous Lipomatous proliferation of synovial membrane (lipoma arborescens). J Bone Joint Surg Am 1988; 70:262-70

2. Yn CH, Wong JWK, Yip DK. Bilateral knee lipoma arborescens: a case report. J Othop Surg (Hong Kong) 2008; 16:107-10

3. Ryu KN, Jaovishida S, Scchweitzer M, Motta AO, Rensink D. MR imaging of lipoma arborescens of knee joint. Am J Roentgenol 1996; 167:1229-32

4. Nambiar M, Onggo JR, Jacobson A. Lipoma arborescens: a rare cause of clicking in the knee. BMJ Case Rep. 2019 Feb 7;12(2):e227949. doi: 10.1136/bcr-2018-227949. PMID: 30737327; PMCID: PMC6381949.

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