Synovial cyst of the cruciate ligament. Findings with magnetic resonance in 8 symptomatic cases

Intraarticular ganglion cysts are uncommon findings: only 30 cases have been reported since the first paper by Caan in 1924 and they were all associated with cruciate ligaments. Many different cystic or pseudocystic lesions are found in articular knee conditions: the most common cystic lesions are popliteal cysts (Baker's cysts), followed by synovial pseudocysts of the posterior cruciate ligament, meniscal cysts and, finally, ganglion cysts of the cruciate ligaments. In our series of 1600 knee MR exams carried out in our MR department since June, 1994, we have found 8 ganglion cysts of the cruciate ligaments. MR studies are always performed on a dedicated 0.2-T permanent magnet (Artoscan, Esaote Biomedica, Genoa, Italy). Five patients were operated on with arthroscopy. The ganglion cysts affected the anterior cruciate ligaments in 4 cases and the posterior cruciate ligaments in 4 cases. The symptoms were mainly pain radiating to the medial side and worsening in forced flexion or extension. The diagnostic suspicion was meniscal tears in 4 patients, chondral lesions in 3 and a loose intraarticular body in one patient. The shape and structure of ganglion cysts in the cruciate ligaments are clearly depicted with MRI. The ganglion cysts in the anterior cruciate ligaments are usually spindle-shaped and within the ligament, while those in the posterior cruciate ligaments have a well-defined outline, with multilocular appearance, and they are usually localized along the ligament, most often on the dorsal aspect. MR signal studies show intermediate signal intensity on SE T1-weighted images and markedly increased signal intensity on SE T2-weighted images. These typical patterns may change depending on lesion content, for instance in the presence of hemoglobin due to an associated angioma. The origin of ganglion cysts in the cruciate ligaments is still unknown, even though many theories have been suggested, including a synovial herniation in ligament fibers, the ectopic inclusion of synovial tissue, a posttraumatic connectival degeneration and, finally, the proliferation of totipotent mesenchymal cells. From a histologic point of view, "synovial ganglion" is a much better definition than "synovial ganglion cyst", because the typical wall of real synovial cysts is missing. The MR patterns are typical of the morphological features described and of the presence of high protein fluid content.