Morphometric analysis of the posterior fossa in adolescents with idiopathic syringomyelia

Objective To investigate the morphometric characteristics of the posterior fossa in adolescents with idiopathic syringomyelia (IS) and to elucidate the clinical significances.Methods A retrospective radiographic review was performed on 25 adolescents who were diagnosed as IS and treated at our clinic between January 2008 and October 2011.Another cohort of normal adolescents and chiari malformation type Ⅰ & syringomyelia(CMI-S) patients,matched with the IS patients in age and gender,were recruited as the control group.Six parameters were assessed in mid-sagittal MR images,including the linear parameters (the length of the clivus,the anteroposterior diameter of the foramen magnum,the length of supraocciput,the anteroposterior diameter of the posterior fossa,the posterior fossa height) and the angular parameter (the clivus gradient).Results In the IS group,the length of the clivus ranged from 25.4 mm to 48.7 mm (mean 38.3 mm) ; the anteroposterior diameter of the foramen magnum ranged from 27.2 mm to 44.2 mm (mean 33.6 mm); the length of supraocciput ranged from 23.6 mm to 48.2 mm (mean 36.7 mm),the anteroposterior diameter of the posterior fossa ranged from 62.9 rmm to 88.4 mm (mean 74.3 mm),the posterior fossa height ranged from 18.51 mm to 43.9 mm (mean 31.3 mm) and the clivus gradient ranged from 30.0 to 77.0 (mean 56.7).Significant differences were observed in all the six morphometric parameters when comparing the IS group and CMI-S group with the normal group respectively.Additionally,all parameters were similar between the IS and CMI-S groups except for the clivus gradient which was significantly larger in the IS group (56.69 ± 10.6,P＜0.05).Conclusions The posterior fossa in patients with IS,sharing the similar characteristics with these in patients with CMI-S,is indeed smaller than normal.A steeper clivus is observed in patients with IS when compared with that in patients with CMI-S. Key words: Syringomyelia;  Cranial fossa, posterior;  Magnetic resonance imaging