Predictive Morphometric Indicators of Surgical Outcome in Chiari I Malformation

Objective:Chiari I malformation (CM-I) is characterized by caudal herniation of the cerebellar tonsils and may lead to variable clinical outcomes following posterior fossa decompression (PFD). This study aimed to investigate whether selected morphometric parameters derived from preoperative and postoperative imaging can predict clinical outcomes after surgical decompression.Methods:This retrospective study included 20 adult patients with CM-I who underwent posterior fossa decompression with C1 laminectomy and duraplasty. Patients were divided into two groups according to postoperative clinical outcome: improved (n=10) and non-improved (n=10). Preoperative and postoperative magnetic resonance imaging and computed tomography were analyzed to measure tonsillar descent below the McRae line, displacement of the iter (DOI), and mammillopontine distance (MPD). Morphometric changes were compared within and between groups using appropriate statistical tests.Results:In the improved group, tonsillar descent showed a statistically significant postoperative reduction (p=0.03), whereas changes in DOI and MPD were not significant. In the non-improved group, none of the morphometric parameters demonstrated significant postoperative change. Comparison of postoperative morphometric values between the improved and non-improved groups revealed no statistically significant differences for any parameter (p>0.05).Conclusion:Although posterior fossa decompression may result in partial radiological improvement, commonly used morphometric parameters such as tonsillar descent, DOI, and MPD do not reliably predict clinical outcome in Chiari I malformation. These findings suggest that static morphometric measurements alone have limited prognostic value, and comprehensive clinical evaluation remains essential for surgical decision-making.