MR morphometric study on posterior cranial cavity in Chiari I malformation with syringomyelia

Objective;MRI was used to measure the posterior cranial structure in order to find out the pathogenesis of syringomyelia in Chiari I malformation.Methods;The posterior cranial structures were measured on midsagittal MR imaging in 114 patients with the herniation of cerebellar tonsil from 3～78 years old (the average age was 38.6),including 62 male and 52 female.There were 60 patients among them with syringomyelia.The anteroposterior diameter(A) of the great occipital foramen,the anteroposterior diameter(B) of the herniated cerebellar tonsil in line A,the vertical diameter (C) of the cerebellar tonsil,the herniated cerebellar tonsil in line A,the vertical diameter(C) of the cerebellar tonsil,the lenght (D) and the anteroposterior diameter(E) of the syringomyelia were measured respectively.SPSS was used for statistical analysis.Results;There was no significant difference in two groups (without and with syringomyelia) in A,B and B/A value.The value of A,B,B/A had no relationship wiht the degree of the herniation of cerebellar tonsil.The value of D and E have the positive correlation with the degree of the herniation of cerebellar tonsil.Conclusion;The herniation of cerebellar tonsil results in continuous impact of the Spinal cord central canal by cranial spinal fluid (CSF).Subsequently causes the water hammer effect,which dilates the central canal gradually,and finally the syringomyelia occurs.The increase of the CSF pressure and the strengthen of CSF pulsation may caue the gradual enlargement of the lenght and the anteroposterior diameter of the syringomyelia.