Magnetic resonance imaging cranial and cerebral dimensions: is there a relationship with Chiari I malformation? A preliminary report in children.

The pathogenesis of idiopathic Chiari I malformation (CM I) remains poorly understood, although it is thought to be due to disproportion between hindbrain structures and the posterior fossa (PF) dimensions. This study was undertaken to determine whether CM I and its possible complications are associated with disproportion between cranial and cerebral dimensions. Surface of the vermis, PF and supratentorial (ST) area were measured on magnetic resonance imaging midsagittal sections and were correlated with age in 19 children with CM I and 43 controls. The ratio of the PF/ST area and of the vermis/PF area were also plotted against age in the two groups and against length of the tonsils herniation in the CM I malformation group. Only the vermis midsagittal area and the vermis/PF ratio were found to be significantly higher in CM I malformation subjects. There was no correlation between the length of tonsils herniation and the vermis/PF area or the PF/ST area ratio in this group. The most severe complications (large syrinx and hydrocephalus) were not associated with particular measurements or calculated ratios in the children with CM I malformation except for the relatively small PF area in a neonate. We conclude that factors responsible for the appearance of clinical signs remain largely unknown. In particular, cranial and brain measurements alone do not seem to predict complications or unfavourable clinical evolution.