Chiari 0 malformation

What it is

Chiari 0 malformation is a described variant in which a person has syringomyelia (a fluid-filled spinal cord cavity) and impaired cerebrospinal fluid flow at the craniocervical junction, but with little or no descent of the cerebellar tonsils. It challenges the idea that herniation is always required.

Understanding Chiari 0 malformation

In Chiari 0, the cerebellar tonsils are not significantly herniated, yet there is a syrinx and evidence of obstructed CSF flow at the skull-spine junction — and, notably, the syrinx may improve after posterior fossa decompression (the same surgery used for Chiari I). This suggests that CSF flow dynamics at the craniocervical junction, not just the amount of tonsillar descent, can underlie Chiari-related problems. Chiari 0 is a relatively recently described and still-evolving concept that broadens the understanding of the condition. It is identified through imaging (including CSF flow studies) and the clinical picture. Understanding Chiari 0 helps explain why some people with a syrinx but minimal herniation may still benefit from decompression.

Why it matters

Understanding Chiari 0 helps families see that Chiari-related problems can occur with minimal herniation, that CSF flow dynamics matter, and that some people with a syrinx but little tonsillar descent may still benefit from decompression.