Lipoma Arborescens of the Knee - MRI

Sagittal T1 weighted MRI in 27 year old male shows a large suprapatellar effusion with a frond-like synovial mass of fat intensity in suprapatellar region and in posterior intercondylar region (arrows).

Sagittal PD FS MRI shows the synovial mass to be the same low intensity as fat (arrows).

Axial gradient echo MRI shows the characteristic frond-like pattern.

Discussion:
Lipoma arborescens is a rare benign lesion, which arises in the synovium and is characterized by villous proliferation of fat cells. The proliferating cells appear organic and often resemble a tree thus its name, arborescens, from the Latin arbor for tree.

Cause: is uncertain. One hypothesis is - synovial hyper-proliferation is in response to traumatic or inflammatory stimuli.

Associations: Trauma, osteoarthritis or rheumatoid arthritis.

Radiograph: Findings are non specific.

1. Soft tissue density with areas of lucency suggesting fat.

2. Underlying degenerative changes of the knee.

MRI: is the investigation of choice.

• Villous proliferation, often with a frond-like configuration, which arises from within the synovial cavity.
• Fatty characteristics and typical pattern of proliferation shows isointense to the fat on all the sequences.
• Joint effusion.
• Meniscal  tears.
• Baker's cyst in 38%.