IS Case 248: Lipoma arborescens

Sam McCabe, MD

Imaging Sciences URMC 2008
Publication Date: 2009-05-26


Patient is a 41-year-old male with chronic painless knee swelling.


There is a large knee joint effusion. Frond-like synovial projections are evident. These follow fat signal on all sequences.


Lipoma arborescens


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.

The clinical differential diagnosis includes other causes of painless joint effusion including pigmented villonodular synovitis (PVNS), synovial osteochondromatosis, and synovial hemangioma.

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.


  1. Hallel T, Lew S, Bansal M. Villous lipomatous proliferation of the synovial membrane (lipoma arborescens). J Bone Joint Surg Am. 1988 Feb;70(2):264-70. [PMID: 3343272 ]
  2. Feller JF, Rishi M, Hughes EC. Lipoma arborescens of the knee: MR demonstration. AJR Am J Roentgenol. 1994 Jul;163(1):162-4. [PMID: 8010204]

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