Pathogenesis of Chiari Malformation: A Morphometric Study of the Posterior Cranial Fossa

Abstract

To investigate overcrowding in the posterior cranial fossa as the pathogenesis of adult type Chiari malformation, we morphometrically studied the brainstem and cerebellum within the posterior cranial fossa as well as the occipital bone while taking into consideration their embryological development.

Compared with the control group, the Chiari group had a significantly larger “volume ratio” as PFBV/PFCV, the three occipital enchondral parts (the basiocciput, exocciput and supraocciput) were significantly smaller and the tentorium was much steeper. There was no significant difference in the posterior fossa brain volume or in the axial lengths of the hindbrain (the brainstem and cerebellum). These results suggest that in adult type Chiari malformation an underdeveloped occipital bone, possibly due to underdevelopment of the occipital somite originating from the paraxial mesoderm, induces overcrowding in the posterior cranial fossa which contains the normally developed hindbrain, and secondary the cerebellar tonsils herniate into the spinal canal.