A Chiari malformation is a problem
in which a part of the brain at the rear of the skull bulges through a normal opening
(foramen magnum) in the skull where it joins the spinal canal. This puts pressure on
parts of the brain and spinal cord. It can cause mild to severe symptoms. In most cases,
the problem is present at birth (congenital).
There are 4 main types of Chiari
malformations (types I, II, III, and IV). Type I is the most common. This article is
about type II. In this type, 2 parts of the brain (the cerebellum and brainstem) bulge
through the foramen magnum.
This problem can happen in newborns
who have spina bifida or spinal myelomeningoceles. A myelomeningocele is when part of
the spinal cord and meninges grow outside the body instead of inside.
A common problem with type II malformations is too much spinal fluid in the brain (hydrocephalus). The extra fluid puts more pressure on the brain. The bones of the skull expand to a larger-than-normal size.