Anterior Clinoid Process in Chiari Malformation Type 2: Measurements, Classifications, Pneumatization Ratio, and Clinical Relevance

Abstract

Objective: To reveal differences in morphologies of the anterior clinoid process (ACP) in patients with Chiari malformation type 2 (CMT2) by comparing normal subjects. Methods: Computed tomography slices of 50 CMT2 (sex: 21 females and 29 males, and mean age: 9.04±5.85 y) and 50 controls (sex: 21 females and 29 males, and mean age: 8.69±5.34 y) were included in the work. The angle (AACP), width (WACP), and length (LACP) of ACP, the width (WOS), and length (LOS) of the optic strut (OS), and the distance (DisOSACP) of OS to ACP were measured. Results: Patients with CMT2 had smaller LACP (P<0.001) and DisOSACP (P=0.007) than controls, but similar WACP, AACP, LOS, and WOS (P>0.05). ACP pneumatization was observed in 10% of CMT2s (10 ACPs) and 12% of controls (12 ACPs). CMT2 did not correlate with the pneumatization (P=0.651). Three configurations regarding ACP pneumatization were detected in CMT2 (types 0: 90%, 1: 8%, and 2: 2%) and controls (types 0: 89%, 1: 9%, and 2: 2%). Four types related to OS position were detected in CMT2 (types B: 5%, C: 30%, D: 51%, and E: 14%) and controls (types B: 3%, C: 15%, D: 69%, and E: 13%). This classification was affected by CMT2 (P=0.041). Conclusions: CMT2s have more anteriorly located OS, and shorter ACP by comparison controls. There is no association between CMT2 and the incidence of ACP pneumatization. Copyright © 2025 Mutaz B. Habal, MD. Unauthorized reproduction of this article is prohibited.