A 50-year-old man, teacher, have a 14-year history of a painless swelling of the left knee which had started in the posterior aspect and had become more diffuse.
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MRI showed villous-like projections in the synovium with fat density, and a large Baker’s cyst.
Lipoma arborescens is a rare, benign intra-articular lesion of unknown aetiology in which there is diffuse replacement of the subsynovial tissue by mature fat cells, with prominent villous transformation of the synovium. Associated conditions have included osteoarthritis, joint trauma, diabetes mellitus; in 20% of the cases popliteal cysts were noted.The knee is most commonly involved, but the condition has also been described in the wrist, shoulder,and hip.
The appearances on MRI are diagnostic and include a synovial mass with a frond-like architecture and a fat-signal intensity on all pulse sequences, which is suppressed using fat-selective presaturation. There is no evidence of magnetic susceptibility effects from haemosiderin; there is an associated effusion and a potential chemical shift artifact.
- Peter Kloen, Suzanne B. Keel, Hugh P. Chandler, Ronald H. Geiger, Bertram Zarins, Andrew E. Rosenberg From Massachusetts General Hospital, Boston, USA