Chiari malformations (CMs) are structural defects in the cerebellum, the part of the brain that controls balance.
When the indented bony space at the lower rear of the skull is smaller than normal, the cerebellum and brainstem can be pushed downward. The resulting pressure on the cerebellum can block the flow of cerebrospinal fluid (the liquid that surrounds and protects the brain and spinal cord) and can cause a range of symptoms including:
There are three primary types of CM. The most common is Type I, which may not cause symptoms and is often found by accident during an examination for another condition. Type II (also called Arnold-Chiari malformation) is usually accompanied by a myelomeningocele-a form of spina bifida that occurs when the spinal canal and backbone do not close before birth, causing the spinal cord to protrude through an opening in the back. This can cause partial or complete paralysis below the spinal opening. Type III is the most serious form of CM, and causes severe neurological defects.
The prevalence of Type I Chiari malformation is estimated to be in the range of one per 1000 to one per 5000 individuals. The incidence of symptomatic Chiari (Type II and Type III) is less than that of Type I, however the prevalence is unknown.
Many people with Type I CM are asymptomatic and do not know they have the condition. Patients with the more severe types of CM that have surgery often see a reduction in their symptoms and/or prolonged periods of relative stability, although paralysis is generally permanent.
Other conditions sometimes associated with CM include:
Medications may ease certain symptoms, such as pain. Surgery is the only treatment available to correct functional disturbances or halt the progression of damage to the central nervous system. More than one surgery may be needed to treat the condition.