Fact-sheet: Lipoma arborescens
Updated on 01/03/2019 at 6:53 PM
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Definition
Lipoma arborescens is of unknown origin and corresponds to a lipomatous proliferation of the synovial membrane villi.
Its association with osteoarthritis, rheumatoid arthritis, or a previous trauma, along with histological findings of chronic synovial inflammation, suggests a nonspecific reactive origin.
Accounts for less than 1% of all lipomas.
Clinical features
Epidemiology:
This lesion mainly affects adult males.
Mean age: 43 years (9-66 years).
Site of predilection: knee (80%), particularly in the suprapatellar recess. Bilateral in 20% of cases.
Clinically: an anterior articular or periarticular knee swelling of progressive onset, mildly painful, often associated with a recurrent, painless joint effusion.
Radiography
In advanced forms, radiographs show degenerative joint changes.
Ultrasound
Proliferation of hyperechoic synovial fronds, associated with a joint effusion
MRI
Diagnosis relies on MRI, showing:
- hypertrophy of the synovial villi (frond-like, "tree leaf" appearance) with fat signal on all sequences.
- usually accompanied by a joint effusion.
- and marked enhancement of the synovial villi after gadolinium injection, reflecting the current "inflammatory" nature of the disease
Differential diagnosis
- Pigmented villonodular synovitis, in which hemosiderin deposits are seen as hypointense on T1, T2, and T2*.
- Synovial lipoma, which is an ovoid or rounded fatty mass without synovial proliferation.
- Synovial hemangioma, a benign vascular tumor in which phleboliths and variable amounts of fatty clusters combined with vessels may be seen.
- Hoffa's disease, which is a hypertrophy of the fat pad located posterior to the patellar tendon.