Intraoperative Subarachnoid Pressure to Predict the Result of Posterior Decompression in Syringomyelia Associated with Chiari Type I Malformation

Summary

The surgical treatment for syringomyelia associated with Chiari type I malformation is reported. Surgical treatment is not yet established because the genesis of syringomyelia has not been clarified. We report here the subarachnoid cerebrospinal fluid flow findings during posterior decompression that correlate to the disappearance of syringomyelia.

During 1991 to 1999, among the patients with syringomyelia associated with Chiari type I malformation on whom we operated, we selected six cases with pos-terior decompression that avoided injuring the arachnoid. We describe here one male and five female patients from 17 to 54 years old (mean, 43.3 years old). Associated disorders were basilar impression, atlantoaxial dislocation, and assimilation of CI to occipital bone in one patient, scoliosis in one patient, and Huntington’s chorea in one patient. We incised the cervical dura linearly with extreme care, under a microscope, to not injure the arachnoid. The dura was incised in a Y-shape toward the cerebellar side. The subarachnoid usually bulged initially so we could avoid injuring the arachnoid. Subarachnoid pressure decreased when the incision was completed, to the cerebellar side, and pulsation was observed. We report how to evaluate subarachnoid CSF pressure during incision of the dura mater to predict the result of syringomyelia. There is good correlation between decompression and decreased syringomyelia size. This technique is not difficult and does not need any special equipment.