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Chiari malformation is a condition in which brain tissue protrudes into your spinal canal. It occurs when a portion of your skull is abnormally small or misshapen, pressing on your brain and forcing it downward. Although Chiari malformation is uncommon, it's now diagnosed more frequently, largely due to improved imaging tests.

Chiari malformation is usually present at birth (congenital), but it can develop in some children after they are born. Signs and symptoms may not occur until adulthood.

Doctors categorize Chiari malformation into several types, depending on the amount of brain tissue that is pushed down into the spinal canal, and whether developmental abnormalities of the brain or spine are present. The more common types are less severe and involve less displaced tissue. Other types are rare and more severe.

Treatment for Chiari malformation depends on its severity and the characteristics of your condition. Regular monitoring, medications and surgery are all treatment options.

Some people with Chiari malformation have no signs or symptoms. Their condition is detected only when tests are performed for unrelated disorders. However, depending on the type and severity, Chiari malformation can cause a number of signs and symptoms.

Signs and symptoms usually start during infancy, although they can begin in adolescence or adulthood. Even when they're less serious, as in the more common types I and II, signs and symptoms still can be problematic and life disrupting.

Headaches, often severe, are the classic symptom of Chiari malformation. They are typically precipitated with sudden coughing, sneezing or straining. People with Chiari malformation type I also can experience:

• Neck pain (running down the shoulders at times)
• Unsteady gait (problems with balance)
• Poor hand coordination (fine-motor skills)
• Numbness and tingling of the hands and feet
• Dizziness
• Difficulty swallowing (sometimes accompanied by gagging, choking and vomiting)
• Vision problems (blurred or double vision)
• Slurred speech

Less often, people with Chiari malformation may experience:

• Ringing or buzzing in the ears (tinnitus)
• Poor bladder control
• Chest pain, in a band-like pattern around the chest
• Curvature of the spine (scoliosis) related to spinal cord impairment
• Abnormal breathing — specifically, sleep apnea characterized by periods of breathing cessation during sleep

Some people have occasional "dropping" episodes — feeling faint and unexpectedly collapsing to the floor, losing consciousness for a few seconds.

In Chiari malformation type II, in which a greater amount of tissue protrudes into the spinal canal compared with type I, the signs and symptoms can include not only those above, but also myelomeningocele, a form of spina bifida in which the backbone and the spinal canal have not closed properly before birth. This type is sometimes called Arnold-Chiari malformation.

In one of the most severe types of the condition, Chiari malformation type III, a portion of the lower back part of the brain (cerebellum) or the brainstem extends through an abnormal opening in the back of the skull.

In people with the even more severe Chiari malformation type IV, the brain itself has never developed normally.

Chiari malformation occurs when the section of the skull containing the cerebellum is too small or is deformed, thus putting pressure on and crowding the brain. There's no clear cause of this misshapen skull.

When the cerebellum is pushed into the upper spinal canal, it can interfere with the normal flow of cerebrospinal fluid (CSF) that protects your brain and spinal cord. This impaired circulation of CSF can lead to the blockage of signals transmitted from your brain to your body, or to a buildup of spinal fluid in the brain or spinal cord. Alternatively, the pressure from the cerebellum upon the spinal cord or lower brainstem can cause neurological signs or symptoms.

Chiari malformation occurs about three times more often in females than in males.

There's some evidence that Chiari malformation runs in some families. However, research into a possible hereditary component is still in its early phase.

If you have any of the signs and symptoms that may be associated with Chiari malformation, see your doctor for an evaluation.

Because many symptoms of Chiari malformation can also be associated with other disorders, a thorough medical evaluation is important. Head pain, for example, can be caused by migraines, sinus disease or a brain tumor, as well as Chiari malformation. Other signs and symptoms overlap with conditions such as multiple sclerosis.

For a thorough examination, your primary care doctor may refer you to a specialist in the brain and nervous system (neurologist) and to a specialist in interpreting X-rays and other imaging (radiologist) to conduct the most appropriate tests.

The diagnostic process begins with your doctor taking your medical history and with a complete physical examination. Your doctor will ask whether you're having symptoms such as head and neck pain, and will ask you to describe them. He or she will also check your fine-motor skills and swallowing ability.

If you have symptoms such as head pain, and the exact cause isn't apparent to your doctor, you'll likely undergo a magnetic resonance imaging (MRI) scan of your skull, which is the definitive diagnostic tool for Chiari malformation.

Using magnetic fields and radio waves, this test produces three-dimensional, high-resolution images of structural abnormalities that may be contributing to your symptoms. It can also provide pictures of the cerebellum and determine whether it extends into the spinal canal. A dye or contrast medium can be injected, and once it travels to your brain, it can enhance the MRI images. An MRI is a safe and painless test. Over time, repeat MRIs can be used to monitor the progression of this disorder.

Your doctor may use other imaging techniques as well. For example, your doctor may recommend a computerized tomography (CT) scan, which uses X-rays in conjunction with a computer to produce precise, sectional images of the bone tissue that surrounds the spinal column.

In some people, Chiari malformation can become a progressive disorder and lead to serious complications. In others, there may be no associated symptoms and no intervention is necessary. The complications associated with this condition include:

• Hydrocephalus. This accumulation of excess fluid within the brain may require placement of a flexible tube (shunt) to divert and drain the cerebrospinal fluid to another area of the body.
• Paralysis. This may occur due to the crowding and pressure on the spinal column. Paralysis tends to be permanent, even after treatment with surgery.
• Syringomyelia. Some people with Chiari malformation also develop a condition called syringomyelia, in which a cavity or cyst (cyrinx) forms within the spinal column. Although the mechanism connecting Chiari malformation with syringomyelia is unclear, it may be associated with injury or displacement of nerve fibers in the spinal cord. When a cavity forms, it tends to be filled with fluid and can additionally impair the function of the spinal cord.
• Death. When a child is born with Chiari malformation type IV, death is common, usually early in infancy.

Treatment for Chiari malformation depends on the severity and the characteristics of your condition. If you have no symptoms, your doctor likely will recommend no treatment other than monitoring with regular examinations.

When headaches or other types of pain are the primary symptom, your doctor may recommend pain medication. Some people experience symptom relief with anti-inflammatory or pain-relieving agents such as indomethacin (Indocin). This approach may prevent or delay the need for an operation.

Reducing pressure by surgery
Surgery is the approach doctors use most often to treat symptomatic Chiari malformation. The goal is to stop the progression of changes in the anatomy of the brain and spinal canal, as well as ease or stabilize symptoms. When successful, surgery can reduce pressure on the cerebellum and the spinal cord, and restore the normal flow of spinal fluid.

In the most common operation for Chiari malformation — called posterior fossa craniectomy or posterior fossa decompression — your surgeon removes a small section of bone in the back of the skull, relieving pressure by giving the brain more room. The covering of the brain, called the dura, is then opened, and a patch is sewn in place to enlarge the covering and provide more room for the brain; this patch may be an artificial material, or it could be tissue harvested from your own leg or neck. The exact technique may vary, depending on whether a fluid-filled cavity is present, or if you have hydrocephalus. The operation takes about two to three hours, and recovery in the hospital usually requires two to four days.

Risks and follow-up
The use of surgery carries risks — the possibility of infection or problems with wound healing. Discuss the pros and cons with your doctor when deciding whether surgery is the best alternative for you. The operation is successful in most people, but if nerve injury in the spinal canal has already occurred prior to surgery, this procedure won't reverse the damage.

After the operation, you'll need regular follow-up examinations with your doctor, including periodic imaging tests to assess the outcome of surgery and the flow of cerebrospinal fluid.