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More than a tongue-twister, Arnold-Chiari malformation is a well-described congenital (present at birth) abnormality of the cerebellum and brain stem. While four different types have been described, types 1 and 2 are most common. Types 2, 3, and 4 are typically diagnosed in infancy because of abnormalities involving the skull or spinal cord. However, type 1, considered a milder form of the condition, may not cause symptoms until adulthood.
In all types, changes affect the posterior part of the brain and spinal cord. Instead of fitting into the posterior fossa, a portion of the cerebellum (the "balance center" of the brain) squeezes through the base of the skull next to the spinal cord. This can cause changes within the spinal cord, ranging from a relative flattening of the cord to a collection of fluid within the cord (called a syrinx). Increased fluid in the brain (hydrocephalus) can also develop.
The headache associated with Arnold-Chiari may take on various forms, including an intermittent form or a persistent one. The pain may be frontal (as in the forehead area) or in the neck or back of the head area. Characteristically, but not always, the pain may worsen with neck movement, coughing, or straining movements. Associated neck pain is a frequent complaint. Upon examination, other problems may be found including incoordination, difficulty swallowing, impaired eye movements, sensory disturbances, and others. Arnold-Chiari is diagnosed by an MRI of the brain and spinal cord but cannot be identified by a CT scan.
If a severe malformation is present, neurosurgery may be needed to eliminate pressure on various parts of the brain and spinal cord and relieve associated symptoms. If surgical intervention is not required, treatment is typically based upon symptoms. For example, daily or periodic (abortive) medications are administered for headaches in a manner similar to treatment for headaches caused by other factors.