Glossary term:

Chiari 0

This curious term clearly implies that there is no Chiari malformation present and yet it is not synonymous with “normal”. People diagnosed as having “Chiari zero” present with symptoms which are typical of an anatomically obvious Chiari malformations but they display apparently normal appearances at the craniovertebral junction, as seen on magnetic resonance imaging. In some cases the imaging reveals a syringomyelia cavity lower down, in the spinal cord, providing further evidence that symptoms are due to some disturbance of cerebrospinal fluid flow across the craniovertebral junction.