Preoperative Predictors of Foramen Magnum Decompression with Dural Splitting for Amelioration of Syringomyelia Associated with Chiari Type 1 Malformation.

OBJECTIVE: Among several procedures for syringomyelia associated with Chiari type 1 malformation (CM-1), foramen magnum decompression (FMD) with dural splitting is one of the treatment choices with low complication rates. However, some meta-analyses have suggested that FMD with dural splitting may be inferior to FMD with duraplasty based on clinical outcomes; therefore, a predictor of a good surgical outcome with dural splitting is essential. This study aimed to clarify the preoperative parameters for good outcomes in patients with FMD with dural splitting, including the volumetric perspective.

METHODS: We reviewed the cases of patients diagnosed with CM-1 and syringomyelia who underwent FMD with dural splitting at our institution. We included patients who underwent magnetic resonance imaging from 6 months to 1 year after surgery and measured radiological parameters using preoperative computed tomography and preoperative/follow-up magnetic resonance imaging.

RESULTS: Thirty-one patients were enrolled. Among all radiological parameters, the volume of the herniated tonsils (Vtonsil) in improved group was significantly smaller, and the difference between the expected volume increment and Vtonsil (Vincr-Vtonsil) in improved group was significantly larger than those in non-improved group. To predict the improvement of the syrinx, Vincr-Vtonsil of 0.77 mL was the optimal cutoff value and yielded 100% sensitivity and 48.0% specificity.

CONCLUSIONS: Vtonsil and Vincr-Vtonsil, which are novel predictors based on the volumetric perspective, might be the optimal predictors for improvement of the syrinx associated with CM-1 by 1 year after surgery.