Cerebellar vermis morphology in children with spina bifida and Chiari type II malformation

Posterior fossa size and cerebellar weight and volume are reduced in Chiari type II malformation (CII). This is assumed to affect the cerebellum uniformly. We quantified the presumed reduction in vermis size on magnetic resonance imaging (MRI).

A midsagittal brain MRI slice was selected from each of 68 participants with CII (mean age 13 years). Control participants were 28 typically developing children (mean age 14.1 years). Midsagittal surface areas occupied by the intracranial fossa, posterior fossa, vermis, and its lobules were measured.

Mean posterior fossa area was significantly smaller (P<0.003), although mean vermis area was significantly larger (P<0.0001), in participants with CII than in control participants. This expansion involved vermis lobules I-V and VI-VII areas (P<0.0001). The midsagittal vermis was expanded and not reduced in size in participants with CII. This is attributed to compressive displacement of midline structures within the confines of a small posterior fossa.