Morphometric Features of Posterior Cranial Fossa are Different between Chiari I Malformation with and without Syringomyelia

Abstract

Introduction To investigate whether the posterior cranial fossa (PCF) morphology in Chiari I malformation without syringomyelia (CMI only) is different from that in Chiari I malformation with syringomyelia (CMI-S). Patients and Methods A total of 14 patients with CMI and without syringomyelia constituted the CMI-only group, whereas 30 patients with CMI and syringomyelia were assigned to the CMI-S group. Another cohort of 30 age-matched asymptomatic adolescents was enrolled to serve as the control group. Six measurements were evaluated and compared between these three groups from T1-weighted magnetic resonance (MR) imaging, including the length of the clivus (AB), the anteroposterior diameter of the foramen magnum (BC), the length of the supraoccipital (CD), the anteroposterior diameter of the posterior fossa (DA), the posterior fossa height (BE), and the clivus gradient (∠α). The PCF morphology in relation to syrinx severity was also investigated. Results Compared with the normal controls, the AB, CD, DA, BE, and ∠α were significantly larger in the CMI-S group. Similar changes in AB, CD, DA, and BE were also demonstrated in the CMI-only group, whereas the clivus gradient (∠α) was found to be relatively normal when compared with the control group. A significantly decreased clivus gradient was observed in the CMI-S groups compared with CMI-only group. In addition, the clivus was significantly flattened in patients with a distended syrinx in comparison to those with a nondistended syrinx. Conclusion Small sizes of the posterior fossa were detected both in CMI cases with and without syrinx. The clivus gradient served as the only morphologic difference in the PCF between CMI-S and CMI-only patients and was correlated with the severity of the syrinx, may support the theory that the restricted circulation of cerebrospinal fluid at the anterior paramedial subarachnoid space contributes to the formation of a syrinx.