[Nerve compression by mucoid pseudocysts: arguments favoring an articular cause in 23 patients]

Mucoid pseudocysts are infrequent benign tumors which can develop on all peripheral nerves near joints. The origin of these cysts remains to be determined. We searched for arguments favoring an articular origin which would have an impact on management and risk of recurrence.

Twenty-three patients (21 men and 2 women, mean age 38 years, age range 13-56 years) presented mucoid pseudocysts and were followed for a mean six years. The mucoid pseudocyst was located on the common fibular nerve at the neck of the fibula in 16 patients, on the tibial nerve at the knee in one, on the median nerve in one, on the ulnar nerve in one, and on the suprascapular nerve in two. Pain was local in 18 patients and irradiated to the concerned nerve territory in 20. Motor deficit was the inaugural feature in 17 patients. EMG was performed in all patients, ultrasound exploration in 15, computed tomography in 7 and magnetic resonance imaging in 10. All patients included in this series underwent surgery: pathological diagnosis of mucoid intra-neural pseudocyst was established in all. Systematic search for communication with the neighboring joint was performed in all cases.

An articular communication was found in 17 patients. Mean time to recovery of muscle force (scored 5) and/or normal sensitivity was seven months in 17 patients. One patient did not achieve full recovery. Three patients experienced recurrence and required tibiofibular arthrodesis.

Three theories have been proposed (cystic degeneration of schwannoma, degeneration of nerve sheath connective tIssue, and an articular origin). The articular theory appears to be the most probable. The presence of an articular pedicle in 60% of the patients, the anatomic juxtaposition between the nerves involved and neighboring joints, and occasional migration along the articular nerve as well as the cyst's mucoid content argue in favor of the articular theory. The notion of recurrence after complete minute excision is also in favor of an articular pathogenic mechanism. The diagnosis of mucoid cyst should be retained as a possibility in patients with rapidly progressive signs of nerve compression near a joint. It is important to search for articular communication before and during the surgical excision in order to limit the risk of recurrence.