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Arnold-Chiari I Malformation

What is Arnold Chiari I Malformation?

Arnold Chiari I Malformation is a congenital condition in which the lowest lying portion of the back of the brain is crowded out of its normal place inside the skull. These downwardly displaced structures, the cerebellar tonsils, can compress parts of the brainstem or upper spinal cord and block the normal flow of spinal fluid into and out of the head.

What are the symptoms of Chiari I Malformation?

These structural abnormalities can lead to headaches as well as a variety of other neurological symptoms including:

  • swallowing problems
  • dizziness
  • vision problems
  • clumsiness
  • spasticity of the limbs
  • sudden “drop attacks” where the legs seem to buckle for no reason

Symptoms may be worse when the neck is flexed or extended.

Many of the most significant neurological symptoms begin during childhood. The most serious complication is a syrinx (syringohydromyelia), a fluid-filled cavity in the spinal cord that can result in permanent numbness and weakness in the arms, among other symptoms.

Chiari I malformations may go unrecognized in adults until something happens that causes symptoms. Scars called adhesions may form over time at the site of compression, resulting eventually in a gradual onset of symptoms. A whiplash-type injury or other accident or trauma may cause sudden onset of symptoms.

The headaches most typical of Chiari I malformations are usually located at the back of the head, and are often made worse by exertion. There is often neck pain and stiffness. It is important to note that true migraine headaches are almost never caused by Chiari I malformations.

How are Chiari I malformations diagnosed?

Diagnosis is typically made by a standard MRI scan. There is a more specialized type of MRI scan that can also detect the blockage of the normal spinal fluid flow caused by the over-crowding.

While the condition is easily identified by MRI, many people with mild Chiari I malformations do not require any treatment at all. In fact, the condition is often completely asymptomatic and commonly found incidentally on brain scans obtained for another reason. Most patients with severe headaches, for example, will eventually have an MRI scan at some point. If it happens that a patient also has a Chiari I, it is easy to jump to the conclusion that the malformation itself is causing the headaches when it may simply be a coincidence. In practice, it is far more common to see patients who have chronic or transformed migraines plus an unrelated and mild Chiari I that is not causing any trouble than it is to see patients with chronic headaches actually caused by the malformation.

What is the treatment for Chiari I malformations?

Adults with a mild form of the Chiari I malformation rarely require surgery, unless there are clear signs or symptoms of brain or spinal cord dysfunction. In these cases, decompression surgery will open up more space for the cerebellum at the back of the head, relieving the pressure on the brainstem and spinal cord. To do this, the cellophane-like lining around the brain (the dura) is typically cut, and often bone is removed as well. Associated syrinxes of the spinal cord usually resolve with the decompression; only rarely will they will require separate surgical drainage procedure.

To ensure that appropriate patients are referred for surgery, each case is carefully considered. For those needing surgery, our Hopkins neurosurgeons are available to assist.

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