Chiari 1 Malformation, Factors That May Influence Decision Making, and Introducing the Chiari 1 Malformation Severity Classification System

<b>Background/Objectives</b>: Chiari 1 malformation (CM-1) is a structural abnormality characterised by cerebellar tonsillar descent of 5 mm or more through the foramen magnum. Despite improved imaging, surgical criteria remain inconsistent. This study evaluates the correlation between classical symptoms, imaging findings, and need for surgical intervention, as well as introducing a novel Chiari 1 scoring system aimed at refining the criteria for management options. <b>Methods</b>: A retrospective study was conducted on adult patients who were evaluated for CM-1 at a tertiary neurosurgical department with a specialised Chiari and Syringomyelia service over 12 months. Data included demographics, symptoms, imaging characteristics, and surgical intervention. Statistical analysis was performed using SPSS Version 30. <b>Results</b>: Sixty-nine (69) patients met the inclusion criteria (mean age, 36.26 years; male-to-female ratio, 1:3.1). Thirty patients (43.5%) had classic symptoms, of whom 26 had a tonsillar descent of >10 mm. A significant association was noted between surgery and classic symptoms (<i>p</i> < 0.01), tonsillar descent of >10 mm (<i>p</i> < 0.01), and syrinx presence (<i>p</i> = 0.02). Our novel scoring system had an AUC of 0.974 (95% CI 0.94-1.00; <i>p</i> < 0.001), with an optimum cut of the value of ≥3 points leading to a sensitivity of 100%, specificity of 89.5%, positive predictive value of 66.7% and negative predictive value of 100%. <b>Conclusions</b>: Surgical intervention remains an effective option for symptomatic patients. Our novel scoring system could provide a simplified, practical, and more accurate method for identifying patients who may benefit from surgical intervention.