Posterior Fossa Measurements in Patients With and Without Chiari I Malformation

Purpose: To determine if there is a correlation between cerebellar tonsillar descent in patients with and without Chiari I malformation and three skull morphometric measurements: clivus length, anteroposterior diameter of the foramen magnum, and Boogard's angle. Methods: Cerebellar tonsillar descent, clivus length, anteroposterior diameter of the foramen magnum, and Boogard's angle were measured in mid-sagittal T1-weighted magnetic resonance images of 188 patients. The study included 81 patients with Chiari I malformations (CMI). Without identifiable pathology, 107 patients served as a comparison group. Two-sample t-tests were used to assess for significance. A Pearson correlation matrix was constructed to assess the strength of linear dependence between measured parameters for the study population. Results: A negative correlation was found between tonsillar herniation and clivus length (r = -0.30, P < 0.001), while a positive correlation was found between tonsillar herniation and foramen magnum size (r = 0.15, P = 0.0431), and Boogard's angle (r = 0.23, P = 0.0014). Clivus length was shorter (P = 0.0009) in CMI patients (4.02 cm +/- 0.45) than comparison patients (4.23 cm +/- 0.42). In addition, the anteroposterior diameter of the foramen magnum was wider (P = 0.0412) (3.74 cm +/- 0.40 compared to 3.63 +/- 0.30) and Boogard's angle was larger (P = 0.0079) (123.58 degrees +/- 8.27 compared to 120.62 degrees +/- 6.79) with CMI. Conclusion: A greater degree of cerebellar tonsillar herniation is associated with a shorter clivus length, a wider anteroposterior diameter of foramen magnum, and a wider Boogard's angle.