What is Arnold-Chiari malformation?
Chiari malformation, also called Arnold-Chiari malformation, is a rare abnormality at the base of the brain that results in brain tissue extending into the upper end of the spinal canal. It may be present at birth (congenital). Chiari malformation is unrelated to Budd-Chiari syndrome, a blockage of the hepatic vein that carries blood away from the liver.
Chiari malformation is divided into several types based on the degree of displacement of the brain tissue into the spinal canal. The most common are Chiari malformation type I and Chiari malformation type II.
In Chiari-I malformation, brain tissue (cerebellar tonsils) protrudes below the opening of the base of the skull (foramen magnum) into the spinal canal. This puts pressure on the brainstem and spinal cord. Chiari-I malformation may also cause displacement of the lower part of the brainstem (medulla). Chiari-I may be associated with:
Some people with Chiari-I have no symptoms. But in others, signs and symptoms may include:
Because cerebrospinal fluid can't drain properly, excess fluid may build up in the brain (hydrocephalus). This usually requires the surgical placement of a shunt system to divert cerebrospinal fluid to another part of the body.
Chiari-II malformation involves a greater degree of brain tissue protruding into the spinal canal. In addition to the cerebellar tonsils, Chiari-II also includes the medulla and a cavity of the brain called the fourth ventricle. Signs and symptoms are similar to Chiari-I. But Chiari-II is usually associated with myelomeningocele, a form of spina bifida.
A doctor may confirm a diagnosis of Chiari malformation by magnetic resonance imaging (MRI) of the skull. Treatment may be considered if symptoms warrant it. The goal of treatment is to halt or reverse the progression of signs and symptoms. Typically, treatment is surgery to relieve crowding at the back of the brain (cerebellum). The success of treatment depends on the individual's specific situation. Surgery may improve some of the signs and symptoms.
Chiari malformation type I
In Chiari malformation type I, brain tissue (cerebellar tonsils) protrudes below the opening of the base of the skull (foramen magnum).
Last Updated: 04/06/2006
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