Causes

Chiari malformation type 1 occurs when the section of the skull containing a part of the brain (cerebellum) is too small or is deformed, thus putting pressure on and crowding the brain. The lower part of the cerebellum (tonsils) is displaced into the upper spinal canal.

Chiari malformation type 2 is nearly always associated with a form of spina bifida called myelomeningocele.

When the cerebellum is pushed into the upper spinal canal, it can interfere with the normal flow of cerebrospinal fluid that protects the brain and spinal cord.

This impaired circulation of cerebrospinal fluid can lead to the blockage of signals transmitted from the brain to the body, or to a buildup of spinal fluid in the brain or spinal cord.

Alternatively, the pressure from the cerebellum on the spinal cord or lower brainstem can cause neurological signs or symptoms.