CausesBy Mayo Clinic staff
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Chiari malformation type I occurs when the section of your skull containing a part of your brain (cerebellum) is too small or is deformed, thus putting pressure on and crowding your brain. The lower part, or tonsils, of the cerebellum are displaced into your upper spinal canal.
Chiari malformation type II is nearly always associated with a form of spina bifida called myelomeningocele.
When the cerebellum is pushed into your upper spinal canal, it can interfere with the normal flow of cerebrospinal fluid that protects your brain and spinal cord.
This impaired circulation of cerebrospinal fluid can lead to the blockage of signals transmitted from your brain to your body, or to a buildup of spinal fluid in the brain or spinal cord.
Alternatively, the pressure from the cerebellum upon the spinal cord or lower brainstem can cause neurological signs or symptoms.
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