The synovial lipoma are uncommon articular tumors of unknown origin. W
e report two cases of synovial lipoma arborescens arisen in a man and
a woman respectively 41 and 27 years old. Both had already consulted f
or a tumefaction progressively increasing in volume. It was accompanie
d in the first case by a laxity in the knee joint. Radiography and art
hroscopy showed an important hyperplasia of the articular synovia. A t
otal synovectomy was performed in both cases. The synovia had a hairy
aspect and was extremely thickened. It weighed 1.5 kg in the first cas
e and its section had a fatty aspect. The histological examination con
firmed the diagnosis of synovial lipoma arborescens. The observed aspe
ct of the two tumors and particularly their volume, which was very imp
ortant in the first case are arguments in favor of their tumoral natur
e.