Posterior cranial fossa MRI morphometric study in Chiari Imalformation

Objective To determine the morphological change and pathogenesis of malformation Chiari Ⅰby measuring the posterior cranical fossa structures.Method The posterior cranial fossa structures on mid－sagittal MR image were measured in 50 patients with malformation Chiari Ⅰand 50 controls without disease of central nervous system .The t－test was used for statistical analysis.Result The cranical cavity and CSF space in posterior fossa malformation with Chiari Ⅰwas significantly smaller than that of control group,the hindbrain position was significantly lower than control group.There was significant difference in the morhpology of posterior cranial fossa and no significant difference in the size of hindbrain between the two groups.Conclusion The narrow posterior cranical cavity,downward displacement of hindbrain,deformed cerebellar tonsilis displaced downward below foramen magnum,and narrow CSF space in the foramen magnum region is the main morphological change of Chiari Ⅰmalformation.In malformation Chiari Ⅰ,the underdeveloped occipital bone indues overcrowding in the posterior fossa,result in the cerebellar tonsilis displaced downwards foramen magnum.