Arnold Chiari Malformation

What Is It?

Arnold Chiari Malformation is a malformation of the brain which can lead to neurological symptoms. There are various forms of the malformation, discussed below, and can be both congenital (present at birth) and acquired. Although the various subtypes of Arnold-Chiari vary in their causes and specific patho-anatomy, the common feature which defines them is the decent of the cerebellar tonsils below the foramen magnum.

The cerebellar tonsils are the most inferior portion of the cerebellum, a part of the hind brain which is important for motor coordination. Normally, these tonsils are wholly inside the skull. In the case of Arnold-Chiari, the tonsils are low-lying, below their normal level. The foramen magnum is the opening at the base of the skull, through which the brain stem passes to become the spinal cord. Whereas the normal cerebellar tonsils sit above the level of this opening, in Arnold-Chiari the tonsils lay below the level of the foramen magnum and can crowd this opening, compressing the brain stem, nerves and fluid pathways in the area.

Common symptoms of this malformation vary depending on the type. The types are listed below with links to further information about the symptoms, diagnosis and treatment of each.


Types of Chiari:


Surgical Treatment for Arnold-Chiari:



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Important Note: This site is not intended to offer medical advice. Every patient is different, and only your personal physician can help to counsel you about what is best for your situation. What we offer is general reference information about various disorders and treatments for your education.

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