Analysis of Clinical and Radiographic Outcomes of the Angle between Clivus and Supraocciput in Patients with Chiari's Malformation Type I Following Surgical Decompression.

The objective of this study was to investigate whether different angles between the clivus and supraocciput (C-SO angle) in patients with Chiari's malformation type I (CMI) after posterior fossa decompression lead to different clinical and radiographic outcomes.  A total of 73 patients who underwent surgical decompression at our institution between 2010 and 2016 were retrospectively divided into two groups: group A, with an angle less than 96 degrees, and group B, with an angle ≥ 96 degrees. Patient clinical outcomes were determined using the Chicago Chiari Outcome Scale (CCOS), and radiographic outcomes were determined by changes in the syrinx size before and after surgery. Direct comparisons were made between the two groups.  There were no statistically significant differences between the two groups regarding demographics, preoperative symptoms or radiographic characteristics (  > 0.05), except for the cerebellar tonsillar descent ( ≤ 0.001). The mean overall CCOS score was 13.11 ± 1.99. The total CCOS score was significantly different between the two patient groups (  < 0.05). Moreover, group A demonstrated significantly better postoperative improvements than group B in clinical outcome measures based on the CCOS system (  = 0.035). For radiographic outcomes, the change in the syrinx between the two groups was also significantly different, with a value  0.024.  A direct comparison between the two groups revealed that a smaller C-OS angle (< 96 degrees) was related to unsatisfactory clinical and radiographic outcomes. Thus, the C-OS angle may emerge as a predictor of clinical or radiographic outcomes following surgical decompression in patients with CMI.