IS Case 248: Lipoma arborescens
Imaging Sciences URMC 2008
Publication Date: 2009-05-26
Patient is a 41-year-old male with chronic painless knee swelling.
Lipoma arborescens (LA) is a rare, idiopathic condition characterized by non-neoplastic synovial and subsynovial fatty proliferation. It is believed to be an atypical response to chronic synovial irritation or degenerative joint disease. It forms frond-like masses in the joint, hence the term "arborescens", meaning "growing like a tree". LA presents with slowly progressive painless joint swelling and intermittent effusions. There is no gender predilection. LA affects adolescents and adults. LA is typically a monoarticular process affecting the knee, although it has been described in the ankle and wrist as well. In the knee, the most common locale is the suprapatellar pouch.
On plains radiographs, a joint effusion is usually seen. There may be relative hyperlucency of the involved area of the joint. MRI has characteristic findings of frond-like synovial projections that follows fat signal on all sequences. LA can be differentiated from PVNS by the absence of susceptibility artifact on gradient echo MR imaging. Other nonspecific associated findings include joint effusion (always present), marginal articular erosions, synovial cysts, joint space narrowing, and osteophytes. The treatment of choice is synovectomy.
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