Foramen magnum decompression with removal of the outer layer of the dura as treatment for syringomyelia occurring with Chiari I malformation.

The surgical results of foramen magnum decompression in seven patients with syringomyelia associated with Chiari I malformations are reported. The patients were two men and five women, ranging in age from 23 to 54 years (mean, 30 yr). A bony foramen magnum decompression combined with the removal of the outer layer of the dura mater was performed in seven patients. In an average postoperative follow-up period of 2 years (range, 1-3 yr), neurological symptoms and signs improved in six of seven patients and were unchanged in one patient. Postoperative magnetic resonance imaging scans taken a few weeks after surgery showed a decrease in the size of the syrinx or a disappearance of the syrinx in five of seven patients; a few months were required for a similar reduction in the remaining two patients. In all seven patients, the decompression of the foramen magnum proved to be sufficient, as disclosed by postoperative magnetic resonance imaging. Foramen magnum decompression by our surgical technique is advantageous because all the procedures are extradural and there are, therefore, fewer postoperative complications than the foramen magnum decompression techniques previously reported. Foramen magnum decompression by the authors' surgical technique is effective as the initial surgical treatment for syringomyelia associated with Chiari I malformations.