Treatment of “idiopathic” syrinx by atlantoaxial fixation: Report of an experience with nine cases

OBJECTIVE: The authors evaluate the significance of atlantoaxial instability in the management of idiopathic syringomyelia. BACKGROUND: We recently observed that atlantoaxial dislocation can be present even when the atlantodental interval was within normal range. Atlantoaxial instability can be identified on the basis of facetal mal-alignment or even by direct observation of status of joint during surgery. Our observations are discussed in nine patients where we identified and treated atlantoaxial instability in cases that would otherwise be considered as having “idiopathic” syrinx. MATERIALS AND METHODS: The authors report experience with nine cases that were diagnosed to have “idiopathic” syrinx. The main bulk of the syrinx was located in the cervico-dorsal spinal region in all cases. One patient had been treated earlier by syringo-subarachnoid shunt surgery and one patient had undergone foramen magnum decompression. RESULTS: On radiological evaluation, eight patients had posterior atlantoaxial facetal (Type B) dislocation. In one patient there was no facetal mal-alignment and was labeled to have axial or central (Type C) facetal instability. All patients were treated by atlantoaxial fixation. All patients improved symptomatically in the immediate postoperative period and the improvement was progressive and sustained on follow-up. In one case, the size of syrinx reduced in the immediate postoperative imaging. In the period of follow-up (range 6–42 months - average 19 months), reduction in the size of syrinx was demonstrated on imaging in three cases. CONCLUSIONS: The positive clinical outcome suggests that atlantoaxial instability may be the defining phenomenon in development of previously considered “idiopathic” syringomyelia.