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Chiari Malformation: A Basic Overview

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What is a Chiari Malformation?
Chiari malformation is a condition that causes brain tissue to settle into the spinal canal. It develops where your skull and neck (cervical spine) come together; when part of the skull is either too small or misshapen, part of the brain can settle into the foramen magnum. The foramen magnum is a large opening at the bottom of your skull. Nerves from the brain go through it and into the spinal canal, joining the spinal cord.

The brain shouldn't press through the foramen magnum; there should only be nerves in there. If the brain does press into the foramen magnum, that's a Chiari malformation.

You can visualize a Chiari malformation by thinking about a funnel. The foramen magnum is the skinny part at the bottom, and above that is where the brain should rest. With a Chiari malformation, though, the brain goes into the skinny part of the funnel.

Causes
Chiari malformation can be caused by a structural problem with the brain, skull, or spinal canal. Those structural problems can be present at birth—those are congenital defects. Chiari malformation caused by structural defects is also called primary Chiari malformation; it isn't caused by any other condition.

Secondary Chiari malformations are caused by something else—most often by surgery. This is very rare, but it is possible to develop a Chiari malformation after having surgery to remove a tumor in the skull/neck area. The surgeon may remove too much bone along with the tumor, allowing the brain to settle into the foramen magnum.

It's also possible to develop a more severe Chiari malformation after surgery to correct a primary Chiari malformation. During a posterior fossa decompression, the surgeon may remove too much bone, making it possible for the brain to settle further into the spinal canal. Again: this is very rare, but it is a possible complication of Chiari malformation surgery, one you should review with your surgeon.

Types
There are four types of Chiari malformations, categorized by how much of the brain is protruding into the spinal canal.

  • Type I: This is the adult version of Chiari malformation, and it's also the most common. It's generally first noticed during adolescence or adulthood, and often, it's discovered during an examination for something else—most people don't realize that they have Chiari malformation, unless the symptoms are quite severe.

    In Type I Chiari malformation, part of the brain settles into the foramen magnum—the cerebellar tonsils, to be exact, is the part going into the foramen magnum.

  • Type II: This is one of the pediatric version of Chiari malformation. More brain tissue pushes through the foramen magnum in Type II: the cerebellar tonsils and a portion of the brainstem protrude. Because more tissue is protruding, the symptoms are more severe with Type II than with Type I.

    Also, Type II always involves myelomeningocele, a form of spina bifida. With myelomeningocele, the vertebrae and spinal canal don't close correctly before birth, so the spinal cord isn't protected.

    Type II is called Arnold-Chiari malformation.

  • Type III: This is also a form that affects children, and it's more severe than Types I or II. In it, a significant portion of the brain—the cerebellum—and the brainstem push all the way through the foramen magnum and into the spinal canal.

  • Type IV: This is the most severe form of Chiari malformation. In Type IV, the brain doesn't develop as it should.

Symptoms
A Chiari malformation can disrupt the flow of cerebrospinal fluid (CSF). CSF is necessary to protect your brain and spinal cord, and if it can't flow normally, then it's more difficult for your brain and spinal cord to send and receive nerve messages.

The pressure caused by parts of the brain pushing through the foramen magnum can also cause nerve problems.

As you can tell, the majority of Chiari malformation symptoms relate to neurological problems. The symptoms do vary based on the type and severity, but the most common symptom is a headache. People with a Chiari malformation generally have headaches in the occipital region of the brain; that's the back of your head, right where you skull joins with your cervical spine (neck). These headaches are generally aggravated by particular positions and actions, including tilting your head back and coughing.

Some other typical symptoms include:

  • weakness
  • balance problems
  • difficulty with fine motor skills (e.g., writing)
  • dizziness
  • vision issues
  • trouble swallowing

For some patients, symptoms can come and go because they're dependent upon how much CSF has built up.

Patients with Type I Chiari malformation may not have any symptoms—it all depends on the severity of the condition.

Diagnosis
The best way to diagnose Chiari malformation is with a magnetic resonance imaging test—an MRI. The MRI will show the doctor the various parts of your brain, skull, spinal cord, and spinal canal; he or she will be able to see any abnormalities that could point to Chiari malformation.

Treatment
The recommended treatment depends on the severity of the Chiari malformation. As mentioned above, it is possible to have Chiari malformation and not have any symptoms—then you won't need treatment.

If you have pain, the doctor may suggest various pain medications to help control the pain. You may need to take a non-steroidal anti-inflammatory (NSAID), a medication that works to reduce inflammation as a way to reduce pain. Or you may need an analgesic—a pain killer. Both NSAIDs and analgesics come in over-the-counter and prescription strength—your doctor will work with you to figure out the best medication for your pain.

Surgery can be used to relieve some symptoms of Chiari malformation; surgery is the only way to relieve the pressure on the spinal cord and nerves caused by the malformation. The goal of surgery is to stop the malformation from getting worse.

Typically, surgeons use a posterior fossa decompression. In that surgery, the surgeon removes part of the skull to make more room for the brain. The surgery takes pressure off the brain and spinal cord—decompression means "to take pressure off"—and should reduce the neurological symptoms and problems. The surgeon may also do laminectomies at C1 and C2—the first and second levels of the cervical spine. The laminectomies are also supposed to make more room for the brain.

Also in a posterior fossa decompression, the surgeon may increase the size of the dura, the sac around the brain. He or she does that by putting in a patch—made from either animal-derived or synthetic tissues—that will grow into the dura. The patch will make the dura bigger, giving more room for the brain. Not every surgery to treat a Chiari malformation will involve this dural patch.

Updated on: 12/10/09
Jason M. Highsmith, MD
This article was reviewed by Jason M. Highsmith, MD.
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