What are Chiari malformations?

Quick Answer
A group of disorders where the cerebellum extends below the opening of the spinal canal (the foramen magnum). Chiari malformations are classified according to severity and how much of the brain extends into the spinal canal: Type I is the most common and may be asymptomatic, type II is considered the classic Chiari malformation, and types III and IV are rare and the most serious.
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Causes and Symptoms

Primary or congential Chiari malformations are a result of structural flaws during fetal development of the brain of spinal canal. The classification of Chiari malformations into four types is based on the extent of the structural flaws. Chiari malformations may also occur after surgery of the head and neck area or after an injury; they are considered secondary or acquired Chiari malformations.

Some individuals with type I do not have any symptoms and may not even know they have a Chiari malformation. This type is considered the adult form of the disorder because often symptoms first appear in adolescence or adulthood. Headaches, neck pain, balance problems, dizziness, hearing and vision problems, and numbness in the arms and legs are the symptoms that result from the pressure on nerves caused by the herniation of the cerebellum into the foramen magnum; the symptoms may come and go. A secondary condition called a syringomyelia may develop in some cases, and it can cause permanent nerve damage.

Type II, also known as an Arnold-Chiari malformation, is considered the classic Chiari malformation. In this type, both the cerebellum and part of the brain stem are pushed into the foramen magnum. Type II is a pediatric disorder, and it almost always involves a form of spina bifida.

Types III and IV, also pediatric disorders, are the most serious forms of Chiari malformations and involve significant brain and neurologic defect. Children with these types do not usually live past two years of age.

Treatment and Therapy

Treatment is not necessary for those individuals who do not have symptoms. Otherwise, treatment is based on the severity of the disorder. Pain medications or nonsteroidal anti-inflammatory drugs (NSAIDs), or both, are used to reduce the pain.

Surgery, specifically some type of decompression surgery, is used to alleviate the pressure on the spinal cord and nerves. Various surgical procedures may be performed to reduce pressure by making more room. One frequently used procedure is a posterior fossa decompression, in which a small piece of the skull at the back of the head is taken out; sometimes a piece of synthetic tissue, called a dura patch, is used to enlarge the area for the brain. Another surgical procedure that is used to relieve pressure and make more room is a laminectomy, in which some of the bony border of the spinal canal is removed.

Other surgical procedures, such as insertion of a shunt for drainage of a syringomyelia or surgical closure of the spinal column in spina bifida, may be necessary. Some surgeries for treatment of the pediatric forms of the disorder are done before birth.

Surgery does not cure Chiari malformations, and it cannot undo the nerve damage that has already occurred. Nevertheless, the various surgical procedures can reduce the pressure and relieve the symptoms. Surgery is not always effective, however, and it is possible that a more severe Chiari malformation may result after surgery.


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National Institute of Neurological Disorders and Stroke. "Chiari Malformation Fact Sheet." NINDS, Apr. 18, 2013.

Novegno, F., M. Calderelli, A. Massa, et al. “The Natural History of Chiari Type I Anomaly.” Journal of Neurosurgery Pediatrics 2, no. 3 (September, 2008): 179–87.

Oakes, W. Jerry, and R. Shane Tubbs. “Management of the Chiari Malformation and Spinal Dysraphism.” In Clinical Neurosurgery, edited by Guy M. McKhann. Denver: Lippincott Williams and Wilkins, 2004.

Parker, James N. The Official Parent’s Sourcebook on Chiari Malformations. San Diego, Calif.: Icon Health, 2003.