The effect of obex position on the development of syringomyelia with morphometric measurements made from the craniocervical junction and posterior fossa in patients with chiari TYPE 1 malformation

Purpose: The aim of this study is to investigate the effect of morphometric measurements made from the craniocervical junction and posterior fossa and the effect of obex position on the development of syringomyelia in patients with Chiari Type 1 malformation (CM-I). Materials and Methods: Between September 2012 and July 2021, 158 patients (107 female, 51 male; age range, 1-76 years; mean age 30,6 years) diagnosed with Chiari Type 1 malformation with brain and cervical MRI examination were included in our study. For each patient; have syringomyelia or not, absence, cerebellar tonsillar herniation degree, syrinx largest diameter, obex position, intracranial volume (ICV), posterior fossa volume (PFV), PFV/ICV ratio, basilar invagination, welcher basal angle, odontoid retroflexion and retroversion angles, CSF flow MRI examinations evaluated separately. In CM-I patients, group means were compared using the Student-t test, and group mean rank was compared using the Mann-Whitney U test. Chi-square test was used to compare the frequencies of categorical variables. The relationship between obex position and herniation degree and syrinx diameter was analyzed by Spearman's test. To predict positivity with syringomyelia, possible factors identified in previous analyzes were analyzed by logistic regression analysis. The Hosmer-Lemeshow test was used for model fit. P<0.05 was accepted as the cut-off value of statistical significance. Findings: In patients with CM-I, the frequency of syringomyelia was significantly lower in the group with platibase (p=0.042). The frequency of syringomyelia was significantly higher in adult (18 years) patients (p=0.007). In patients with or without syringomyelia with CM-I; no statistically significant difference was found in terms of the degree of cerebellar tonsillar herniation, the largest diameter of the syrinx, obex position, PFV/ICV ratio, basilar invagination, odontoid retroflexion and retroversion angles, and CSF flow MRI examinations. Results: We think that basal angle measurement can be used as a radiological evaluation in patients with Chiari Type 1 malformation (CM-I), as a result of welcher basal angle measurement, syringomyelia is seen less frequently in patients with platibase, and in pre-stretching the development of syringomyelia. Key Words: Chiari Type 1 malformation (CM-I), syringomyelia, obex position, platybasia, welcher basal angle, Magnetic Resonance Imaging (MRI).