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Genetic and Rare Diseases Information Center (GARD)

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Chiari malformation type 1


* Not a rare disease
Other Names for this Disease
  • Arnold Chiari malformation type I
  • Chiari malformation type I
  • Chiari type I malformation
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What is Chiari malformation type 1?

What causes Chiari malformation type 1?

How might Chiari malformation type 1 be treated?

What is Chiari malformation type 1?

Chiari malformation type 1 is a structural abnormality of the cerebellum, the part of the brain that controls balance. It involves the extension of the lower part of the cerebellum into the foramen magnum (the large hole at the base of the skull which allows passage of the spinal cord), without involving the brainstem. Normally, only the spinal cord passes through this opening. This malformation is the most common type of Chiari malformation and may not cause any symptoms.[1] Depending on the symptoms present and severity, some individuals may not require treatment while others may require pain medications or surgery.[2][3]
Last updated: 3/12/2012

What causes Chiari malformation type 1?

Primary or congenital Chiari malformations are caused by structural defects in the brain and spinal cord that occur during fetal development. The underlying cause of the structural defects are not completely understood, but may involve genetic mutations or lack of proper vitamins or nutrients in the maternal diet.[1]

Less frequently, Chiari malformation type 1 is acquired after birth. Causes of acquired Chiari malformation type 1 involve the excessive draining of spinal fluid from the lumbar or thoracic areas of the spine as a result of injury, exposure to harmful substances, or infection.[1] Click here to view a diagram of the spine.

Last updated: 3/12/2012

How might Chiari malformation type 1 be treated?

Some individuals with Chiari malformation type 1 are asymptomatic and do not require treatment.[2] Individuals who have minimal symptoms, without syringomyelia, can typically be treated conservatively. Mild neck pain and headaches can usually be treated with pain medications, muscle relaxants, and the occasional use of a soft collar.[3]

Individuals with more severe symptoms may be in need of surgery.[3] Surgery is the only treatment available to correct functional disturbances or halt the progression of damage to the central nervous system.[2] The goals of surgical treatment are decompression of the point where the skull meets the spine (the cervicomedullary junction) and restoration of normal flow of cerebrospinal fluid in the region of the foramen magnum (the hole in the bottom of the skull where the spinal cord passes to connect to the brain).[3] Prognosis after surgery for the condition is generally good and typically depends on the extent of neurological deficits that were present before the surgery. Most individuals have a reduction of symptoms and/or prolonged periods of relative stability. More than one surgery may be needed to treat the condition.[2][3]
Last updated: 3/12/2012

  1. Chiari Malformation Fact Sheet. National Institute of Neurological Disorders and Stroke Web site. 2009; Accessed 12/22/2009.
  2. Chiari Malformation Fact Sheet. NINDS. February 1, 2012; Accessed 3/11/2012.
  3. Peyman Pakzaban. Chiari Malformation. eMedicine. March 2, 2012; Accessed 3/11/2012.