[Arthroscopic treatment of a Hoffa ligament cyst].

Cysts of Hoffa's ligament are exceptional. Twelve cases have been reported in the literature, two of which were treated arthroscopically. We report the first case in the French literature. A 21-year-old woman developed an atypical cystic formation of the knee. The diagnosis of ganglion cyst of Hoffa's ligament was strongly suggested at magnetic resonance imaging and confirmed at arthroscopy. We recall the different epidemiologic, pathogenic, clinical and radiological aspects of this condition and emphasize the importance of MRI for the differential diagnosis with other tumors.