The Relationship of the Posterior Cranial Fossa, the Cerebrum, and Cerebellum Morphometry with Tonsiller Herniation

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Background: Tonsillar herniation is a condition that manifests as herniation of the brain parts, originating from the hindbrain and progressing through the foramen magnum into the cervical vertebral canal. Although the etiology of tonsillar herniation is unclear, it has been suggested that it may be congenital or acquired. In particular, there is speculation that primary mesodermal insufficiency may affect the size of the posterior cranial fossa. Objectives: Our main objective is to perform measurements of the cranium, cerebrum, and cerebellum in order to clarify the etiology of tonsillar herniation. Patients and Methods: Magnetic resonance images were taken for 1,052 patients (629 females and 423 males) with no disease affecting the bones. Chiari malformation type I (CMI) was detected in 63 of the patients. The remaining 989 patients were considered to be the control group. The patients’ mean age was 36.58 ± 22.34 (1 - 94 years). Measurements were performed using midsagittal and axial T1 and T2 images. Nine parameters were used to evaluate cranium morphometry, while a further nine were used to evaluate cerebrum and cerebellum morphometry. The data collected were analyzed using SPSS version 14 statistics software, in addition to the t-test and the Mann-Whitney U test. The significance level was set at 0.05. Results: In individuals with tonsillar herniation, while the front-back diameter of the foramen magnum, the cerebellum height, and the sagittal diameter of the cerebellum increased, the maximum cranial height, supraocciput length, clivus length, and height of the posterior cranial fossa decreased. Also, in the case of all age groups, there was no statistically significant difference between the healthy controls and the people with tonsillar herniation in terms of tentorial slope angle. The mean herniation value was 4.85 ± 3.09 mm in those with tonsillar herniation. Conclusion: Our results concerning cranium morphometry support the theory that hypoplastic posterior cranial fossa due to mesodermal insufficiency may play a role in the etiology of tonsillar herniation.