Posterior cranial fossa dimensions in Chiari I malformation relates to the degree of cerebellar tonsillar descent and syringomyelia

Objective To measure the linear structures of posterior cranial fossa in Chiari I malformation(CMI) patients base on fMRI techniques and to investigate the causes associated with different degrees of cerebellar tonsillar descent and syringomyelia.Methods A retrospective radiographic study was performed for 97 CMI patients who were treated in Jishuitan hospital during 2004-2012.According to the degree of cerebellar tonsillar descent,CMI patients were divided into three categories:CMI Ⅰ in 48 cases(49.5%),CMI Ⅱ in 36 cases(37.1%),and CMI Ⅲ in 13 cases(13.4%).According to the radiographic demonstration,patients were divided into two categories:patients with syringomyelia which accounted for 69 cases(71.1%) in total,and patients without syringomyelia which accounted for 28 cases(28.9%).The t-test was performed for statistical analysis.Results For patients with CMI Ⅰ,the following statistically significant differences were identified when compared with patients with CMI Ⅱ and CMI Ⅲ:increased length of clivus(d+e),increased length of the basiocciput(e),increased length of hindbrain(b),increased length of cerebellar hemisphere(c)(P 0.05).For patients with syringomyelia,the McRae's line(B to OP) significantly reduced when compared with those without syringomyelia.However,the length of hindbrain(b) was longer in the syringomyelia group.Conclusion In CMI patients,the main causes of cerebellar tonsillar descent and syringomyelia are the abnormalities of both bony and neural structures in posterior cranial fossa.Surgical strategy to modify the malformation in this area was recommended.