Morphological study of bone structure of the posterior cranial fossa in adults with Chiari malformation type Ⅰ without basilar invagination

Abstract

Objective To examine the morphological characteristics of the bone structure in the posterior cranial fossa in adult patients with Chiari malformation type Ⅰ (CMⅠ) without basilar invagination. Methods Thirty-eight adult patients with CMⅠ without basilar invagination treated in our department between January, 2018 and June, 2020 were enrolled in this study as the observation group, and 38 gender- and age-matched healthy adults served as the control group. The differences in the linear and angular variables in the posterior cranial fossa were analyzed between the 2 groups based on thin-slice CT data. Results Compared with the control subjects, the patients with CMⅠ showed significantly decreased clivus length (P < 0.001), supra-occipital length (P < 0.01), occipital length (P < 0.01), Klaus height index (P < 0.001), posterior compressive value (P < 0.01), tentorial angle (P < 0.05) and sagittal area of the bony posterior cranial fossa (P < 0.001) and significantly increased odontoid compressive value (P < 0.01), odontoid and soft tissue compressive value (P < 0.01), anterior compressive value (P < 0.01) and basal angle (P < 0.01). Conclusion In adult patients with CMⅠ patients but without basilar invagination, the clivus and occipital bone are shortened and elevated with co-existing ventral cervicomedullary compression by the posterior margin of the odontoid process.

Keywords

• chiari malformation
• basilar invagination
• computed tomography
• posterior cranial fossa