[Lipoma arborescens of the knee joint ].

To cite: Erol B, Ozyurek S, Guler F, et al. BMJ Case Rep Published online: [please include Day Month Year] doi:10.1136/bcr-2013009271 DESCRIPTION A 26-year-old woman presented to our orthopaedic clinic with a difficulty in walking, prolonged pain and recurrent swelling in her left knee joint for the previous 2 years. On physical examination, there was no limitation in the range of motion of the knee; however, both flexion and extension were painful. Other findings were normal. In the laboratory findings, erythrocyte sedimentation rate and C reactive protein were slightly above normal. MRI revealed effusion and villous thickening with a similar signal as the fat tissue in all sequences of synovial membrane which was more prominent in the suprapatellar of the left knee (figure 1A–D). MRI also demonstrated frond-like projections. These findings were consistent with lipoma arborescens (LA). The synovial mass with villonodular thickening was excised with arthrotomy and synovectomy. Histopathological examination revealed a lesion which formed villous structures and contained synovial epithelium with hyperplastic form and a mature adipose tissue, hence it was reported as LA (figure 2). LA is a rare, benign lesion characterised by lipomatous villous proliferation of the synovial membrane. Its aetiology is unknown. Though it occurs in the knee joint most commonly, it may also occur in other joints. LA presents with painless, slowly progressing swelling associated with intermittent joint effusions. MRI is the best modality to