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Chiari (kee-AR-ee) malformation is a serious neurological disorder where the lower part of the brain, the cerebellum (which controls balance and coordination) descends into the spinal canal. Since the skull is not big enough, the tips of the cerebellum, called the cerebellar tonsils, are pushed down through the foramen magnum (the bottom part of the skull) where the brain attaches to the spinal cord. The tonsils obstruct the normal flow of cerebral spinal fluid (CSF, which surrounds and protects the brain and spinal cord) and the resulting pressure on both the brain and spine causes many symptoms.
Many Chiarians (people with Chiari) also suffer from syringomyelia (sear-IN-go-my-EEL-ya), a disorder in which a fluid-filled cyst (or syrinx) forms within the spinal cord. The syrinx can expand over time and, if not treated, can cause paralysis.
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Chiari malformation is named after Dr. Hans Chiari, an Austrian pathologist, who classified the malformations into Types I to III in 1891. There is also a Type IV.
There are roughly 300,000 people diagnosed with Chiari in the United States, although that statistic may not accurately reflect the true number of Chiarians in our country. As more doctors become aware of Chiari and access to MRIs become more readily available, we believe that the number will rise. Chiari is seen around the globe, so most likely there are millions of Chiarians worldwide.
Females are affected three times more often than males. It is usually congenital (present at birth). If left untreated, it can cause paralysis in some people. Death usually affects those with Chiari III or IV, which are rare.
Chiari I is the most common and the posterior fossa (back area of the skull) is too small or poorly shaped.
Chiari II is usually seen in infants born with myelomeningocele (my-e-lo-MENING-o-seal), a type of spina bifida in which the backbone and spinal canal do not close before birth. It also involves more of the brain than Chiari I. The symptoms are the same, but are usually worse and occur earlier.
Chiari III is an extremely severe condition and is rarely survivable. In Chiari III, a portion of the brain extends through an abnormal opening in the back of the skull.
Chiari IV is also rare and the patient has a slim chance of surviving. In Chiari IV, the brain itself has not developed normally.
While the cause of Chiari is unknown, the most common treatment is posterior fossa decompression surgery to either relieve or prevent further progression of the symptoms. A neurosurgeon will then remove a small part of the back of the skull and part of the first vertebrae of the spine to widen the bottom part of the skull. Dura mater, the tough membrane that covers the brain in the affected area, is opened up and a dural patch (tissue taken from either the patient, a cow or a cadaver) is sewn to expand the space and restore normal CSF flow.
University of Wisconsin Hospital and Clinics, Princeton Brain & Spine Center, Seattle Children’s Hospital, Research and Foundation, Mayfield Clinic, CNN Health, The Chiari Institute, Child Neurology Education and Research Foundation, Mayo Clinic.
This publication is for information purposes and is not intended as medical advice.