What is a Chiari malformation?
A Chiari malformation is a congenital (present at birth) defect in the area of the back of the head where the brain and spinal cord connect. The condition is also called Arnold Chiari malformation. There are four types of Chiari malformations, including the following:
- Type I. Commonly goes unnoticed until problems arise in the adolescent or adult years of life. In this condition, the base of the skull and the upper spinal area are not formed properly.
- Type II. This is the most common type of Chiari malformation. In this condition, part of the back of the brain shifts downward through the bottom of the skull area.
- Type II Chiari malformations are typically seen in infants who are born with spina bifida, a neurological condition that causes a portion of the spinal cord and the surrounding structures to develop outside, instead of inside, the body.
- Type II Chiari malformations can also be associated with a condition known as hydrocephalus. Hydrocephalus is a condition in which there is an overproduction or lack of absorption of the cerebral spinal fluid (CSF) that is found inside of the ventricles (fluid-filled areas) inside of the brain. The increased fluid causes the pressure inside of the head to increase and the skull bones to expand to a larger-than-normal appearance.
- Type III. The back of the brain protrudes out of an opening in the back of the skull area.
- Type IV. The back of the brain fails to develop normally.