Congenital Chiari malformation

What it is

Congenital Chiari malformation is Chiari malformation that is present from birth, arising from the way the skull base and brain developed. It is the usual situation for most Chiari malformations, including types I and II.

Understanding Congenital Chiari malformation

Most Chiari malformations are congenital, developing before birth — type I often linked to a small or underdeveloped posterior fossa (the bony compartment failing to provide enough room), and type II to abnormalities associated with spina bifida. Although congenital, type I may not cause symptoms until later childhood or adulthood (or ever), so being congenital does not mean symptoms are present from birth. Recognizing that Chiari is usually a developmental condition helps explain its associations (such as with genetic and connective-tissue conditions) and distinguishes it from the rarer acquired forms that develop later due to another cause. Understanding the congenital nature helps frame the condition's origins.

Why it matters

Understanding that Chiari is usually congenital helps families see that it typically arises from how the skull and brain developed — even when symptoms appear later — and distinguishes it from rarer acquired forms with a specific later cause.