Analysis of the cranial aperture of the optic canal in Chiari type I malformation.

This retrospective computed tomography investigation aimed to view morphological properties of the cranial aperture of the optic canal (CAOC) in Chiari type I malformation (CIM). Radiologic images of 40 CIM patients (24 females / 16 males, mean age: 20.75±14.98 years) and 40 normal subjects (24 females / 16 males, mean age: 23.13±18.89 years) were included in the work to investigate anatomical features of CAOC. CAOC width (p=0.137), CAOC height (p=0.243), the distance between CAOC and midsagittal line (p=0.982), and the angle of the optic canal in sagittal plane (Ang-in-SP) (p=0.598) were similar in CIM and controls. Compared to controls, the distances between CAOC and the anterior (Dis-to-AB) and lateral (Dis-to-LB) boundary of the anterior skull base were observed smaller in CIM (p 0.01), but the angle of the optic canal in axial plane (Ang-in-AP) were observed greater in CIM. Four different aperture shapes were identified in CIM group (tear-drop: 42 sides, 52.40%; triangular: 17 sides, 21.30%; oval: nine sides, 11.30%; and round: 12 sides, 15%) and the control group (tear-drop: 36 sides, 45%; triangular: 14 sides, 17.50%; oval: 10 sides, 12.50%; and round: 20 sides, 25%). Greater Ang-in-AP, and shorter Dis-to-LB and Dis-to-AB were found in CIM compared to controls. The distance measurements display that CIM patients have less anterior fossa length and width than normal subjects.