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Chiari Malformation Type I

What is a Chiari malformation?

A Chiari malformation is a problem in which a part of the brain at the rear of the skull bulges through a normal opening (foramen magnum) in the skull where it joins the spinal canal. This puts pressure on parts of the brain and spinal cord, and can cause mild to severe symptoms. In most cases, the problem is present at birth (congenital). 

There are several types of Chiari malformations, but type I (CM-I) is the most common type. In type I, part of the cerebellum bulges through the foramen magnum. This type is most often congenital (also called primary CM-I), but is often not found until a person is a teen or young adult. In rare cases, this type may also develop later in life. This is known as acquired or secondary CM-I.

What causes a Chiari malformation type I?

The exact cause of a congenital Chiari malformation type I is not known. A problem during fetal growth may cause the defect. It may be caused by contact with harmful substances during pregnancy. Or it may be linked with genetic problems that run in families.

An acquired Chiari malformation type I happens to a person after birth. It is caused by excess leaking of spinal fluid from the lower back (lumbar) or chest (thoracic) areas of the spine. This can happen because of an injury, contact with harmful substances, or an infection.

What are the symptoms of a Chiari malformation type I?

You may not have any symptoms. Or symptoms may develop slowly over time. Most people don't have symptoms until they are teens or young adults.

The most common symptoms are headaches or pain in the back of the head or neck. The headaches and pain are made worse by coughing, laughing, or sneezing.

Other symptoms of a Chiari malformation type I are:

  • Hoarseness or  trouble speaking

  • Trouble swallowing

  • Rapid, back and forth eye movements (nystagmus)

  • Periods of not breathing during sleep (sleep apnea)

  • Weakness or abnormal movements

  • Trouble with balance

  • Abnormal reflexes

  • Abnormal shape of the spine (scoliosis)

You may also have a pocket of fluid in the spinal cord or brain stem. This is called a syrinx. A syrinx can cause trouble walking or pain in the arms or legs.                      

How is a Chiari malformation type I diagnosed?

If you have no symptoms, the defect may be found when you have imaging tests for other reasons. If you have symptoms, your health care provider will ask about your medical history and give you a physical exam. He or she may refer you to a specialist.

Imaging tests are done to detect a Chiari malformation type I. Your child may have 1 or more of these tests:

  • MRI. This test is the one most often used to diagnose Chiari malformations. It uses large magnets and a computer to make detailed pictures of the inside of the body.

  • CT scan. This test uses a series of X-rays and a computer to create detailed pictures of the inside of the body. A CT scan is more detailed than a regular X-ray.

How is a Chiari malformation type I treated?

You may be treated by a neurologist or neurosurgeon. These are experts in brain and spinal cord problems. Treatment will depend on your symptoms, age, and general health. It will also depend on how severe the condition is.

  • With no symptoms. Your health may be watched closely. This may include frequent physical exams and MRI tests.

  • With symptoms. Your health care provider may prescribe medicines to reduce pain. Or he or she may choose surgery. This is done to relieve pressure on the brain or restore the flow of spinal fluid.

  • With few or no symptoms, but a syrinx. Your health care provider may suggest close monitoring of the defect with a special type of MRI called cine phase contrast. This test looks at the flow of spinal fluid. It also looks at areas where the fluid is blocked. You may need surgery, based on the MRI results or if symptoms get worse.

  • With signs of sleep apnea. You may need a sleep study if you have sleep apnea. Sleep apnea means that you stop and start breathing during sleep. A sleep study can also help your health care provider decide if you need other treatment.

What other health problems are caused by a Chiari malformation type I?

These health problems can include:

  • Long-term pain

  • A syrinx. This is a pocket of fluid in the spinal cord or brain stem. This forms over time.

  • Life-long damage to muscles or nerves

  • Paralysis. This means your arms or legs can’t move because the muscles no longer work.

Carefully watching for changes in your health can help prevent these problems. This helps to make sure that treatment is done early.                                                              

When should I call my health care provider?

Call your health care provider if you notice any changes. Be sure to call if you notice problems with:

  • Breathing

  • Swallowing

  • Feeding

  • Speaking

  • Walking or moving

Key points about Chiari malformation type I

  • With a Chiari malformation, the lower part of the brain dips down through a normal opening at the bottom of the skull. In some cases, more brain tissue also dips down through this opening.

  • In most cases, the problem is present at birth (congenital). 

  • There are several types of Chiari malformations. Type I is the most common type.

  • You may not have symptoms. If symptoms occur, the most common ones are headaches or pain in the back of the head or neck. The headaches and pain are made worse by coughing, laughing, or sneezing.

  • You may also have a pocket of fluid in the spinal cord or brain stem. This is called a syrinx.

  • Imaging tests are done to detect a Chiari malformation type I. You may have an MRI or a CT scan.

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