Chiari Type 1 malformation: CSF flow dynamics and morphology in the posterior fossa and craniocervical junction and correlation of these findings with syrinx formation.

BACKGROUND: Chiari type 1 malformation (CMI) is a disorder in which cerebellar tonsils descend below the foramen magnum. Although syringomyelia associated with CMI thought to be caused by hypoplastic posterior fossa and stenosis at the craniocervical junction; it has characteristic neurological and radiological features and the exact mechanism of syringomyelia remains unknown.

PURPOSE: The purposes of this study were to gain insight into morphological changes in posterior fossa and to find whether there is a difference in aqueductal stroke volume (ASV) between CMI with syrinx and without syrinx which may be an underlying mechanism of syrinx development.

MATERIALS AND METHODS: We consecutively evaluated 85 patients with Chiari malformation between January 2017 and December 2019 who had undergone phase-contrast MRI examination for CSF flow and between 18-60-years-old. We divided patients into two groups as subjects with syrinx (n=19) and without syrinx (n=66). After evaluating morphological changes, peak and average velocity (cm/s), forward and reverse flow volume (μl), net forward flow volume (μl), ASV (aqueductal stroke volume) (μl), aqueductus Sylvi (AS) area (mm2 ), and prepontine cistern diameter to AS diameter ratio (PPC/AS) were calculated. Distribution of variables from two groups was evaluated by using Shapiro-Wilk normality test. Independent t test was used for groups comparison.

RESULTS: The forward and reverse volumes were statistically significantly higher in patients with syrinx (P=0.021, P=0.005 respectively). ASV was significantly increased in patients with syringomyelia (P=0.014). The PPC/AS was significantly lower in patients with syrinx compared to those without (P <0.001). AS area was significantly larger in those with syrinx. (P=0.022). The diameter of foramen magnum was significantly lower in patients with syrinx than those without (P <0.0001). The diameter of the herniated tonsilla at the foramen magnum level was found to be significantly lower in those with syrinx (P=0.011).

CONCLUSION: Foramen magnum diameter, ASV, diameter of herniated tonsil, and PPC/AS ratio are important factors in syrinx development.