Morphometric analysis of posterior fossa in adult Chiari malformation type Ⅰ and its correlation with syringomyelia and the extent of cerebellar tonsillar displacement

English Keywords:Adult Chiari malformation type Ⅰ  Posterior fossa volume  Morphometric analysis  Syringomyelia

English Abstract:

  【Abstract】 Objectives: To determine the characteristics of the posterior fossa linear volume in adult patients with Chiari malformation type Ⅰ(CMⅠ) and its association with the extent of cerebellar tonsillar displacement and syringomyelia. Methods: A retrospective radiographic study was performed on adult patients with CMⅠ who were treated in our hospital between June 2010 and June 2014. The inclusion criteria were as followings: (1)age more than 30 years old; (2)the diagnosis of CMⅠ in each patient was confirmed by a combined head and cervical spine MRI; (3)patients with skull fracture or other diseases which can lead to secondary CMⅠ were excluded. Age-matched healthy adults were recruited as control group. The length of clivus, the anteroposterior diameter of foramen magnum, the length of supraocciput, the anteroposterior diameter of posterior fossa, the posterior fossa height and the clivus angle were measured on the mid-sagittal MRI images to compare the posterior fossa volme between adults CMⅠ patients and controls. Then a further analysis was performed to determine the association between the posterior fossa volum in adult CMⅠ patients and the severity of cerebellar tonsillar displacement as well as the syringomyelia. Results: 37 CMⅠ patients (18 males and 19 females) with a mean age of 38.5±5.5(31-56) years old were recruited in this study. 41 healthy adults(19 males and 22 females) were recruited as the control group with a mean age of 36.4±6.3(33-58) years old. The length of clivus, the length of supraocciput, the anteroposterior diameter of posterior fossa, the posterior fossa height and the clivus angle of CMⅠ patients were 35.9±4.2mm, 38.2±5.8mm, 77.4±6.1mm, 28.2±3.9mm and 47.4°±6.4° respectively, which differed significantly with the indexes in the control group(43.92±2.9mm, 43.5±5.6mm, 82.5±4.5mm, 35.4±3.4mm and 58.6°±5.7°, P＜0.05). The clivus angle was significantly smaller in CMⅠ patients with syingomyelia than that in those without syingomyelia(45.8°±7.6° vs. 49.7°±5.1°, P＜0.05). The length and angle of clivus were significantly smaller in CMⅠ patients with Ⅱ grade tonsillar descent(31.4±3.6mm and 42.3°±5.4°) than those in grade Ⅰ patients(36.2±3.8mm and 48.1°±5.2°, P＜0.05). Conclusions: The bony component of posterior fossa decreases in adult CMⅠ patients, but it is not correlated to the presence of syringomyelia or the severity of cerebellar tonsillar denscent. Maldevelopment of clivus is correlated to the presence of syringomyelia and the severity of cerebellar tonsillar denscent in CMⅠ patients.