What is Chiari malformation?

Chiari malformation (CM) is a structural abnormality in the relationship of the skull and the brain. This means that the skull is small or misshapen, causing it to press on the brain at the base of the skull. It can cause brain tissue to extend into the spinal canal.

CM affects the portion of your brain called the cerebellum. It’s located behind the brain stem, where the spinal cord meets the brain. When the cerebellum pushes into the spinal canal, it can block the brain’s signals to your body. It can also cause fluid to build up in your brain or spinal cord. This pressure and buildup of fluid can cause a variety of neurological symptoms. The symptoms typically involve balance, coordination, vision, and speech.

CM is named after Austrian pathologist Hans Chiari, who described and categorized the abnormalities in the 1890s. It’s also known as Arnold-Chiari malformation, hindbrain herniation, and tonsillar ectopia.

Read on to learn more about this condition, from types and causes to outlook and prevention.

If CM develops during the fetal stages, it’s known as primary or congenital CM. Several factors may cause primary CM:

  • Genetic mutations may cause the fetus to develop abnormally.
  • Lack of proper vitamins and nutrients during pregnancy, such as folic acid, may affect fetal development.
  • Infection or a high fever during pregnancy may affect fetal development.
  • Exposure to hazardous chemicals, illegal drugs, or alcohol during pregnancy may affect fetal development.

Sometimes CM can occur in adulthood as a result of an accident or infection where the spinal fluid is drained out. This is known as secondary CM.

Type 1: Type 1 is the most common type of CM. It involves the lower part of the cerebellum known as tonsils, but not the brain stem. CM type 1 develops when the skull and brain are still growing. Symptoms may not appear until teen or adult years. Doctors usually find this condition accidentally during diagnostic tests.

Type 2: Also known as classic CM, type 2 involves both cerebellar and brain stem tissue. In some cases, the nerve tissue that connects the cerebellum together may be partially or completely missing. It’s often accompanied by a birth defect called myelomeningocele. This condition occurs when the backbone and spinal canal don’t close normally at birth.

Type 3: Type 3 is a much rarer, but more serious malformation. Brain tissue extends into the spinal cord, and in some cases parts of the brain may protrude. It can involve severe neurological defects and may have life-threatening complications. It’s often accompanied by hydrocephalus, an accumulation of fluid in the brain.

Type 4: Type 4 involves an incomplete or undeveloped cerebellum. It’s usually fatal in infancy.

Type 0: Type 0 is controversial for some clinicians because it has minimal to no physical changes to the cerebellar tonsils. It may still cause headaches.

In general, the more brain tissue that pushes into the spine, the more severe the symptoms. For example, someone with type 1 may not have any symptoms, while someone with type 3 may have severe symptoms. People with CM can have a variety of symptoms, depending on the type, buildup of fluid, and pressure on tissues or nerves.

Since CM affects the cerebellum, symptoms typically involve balance, coordination, vision, and speech. The most common symptom is a headache at the back of the head. It’s often brought on by activities like exercising, straining, bending over, and more.

Other symptoms include:

  • dizziness
  • neck pain
  • numbness or tingling in hands and feet
  • trouble swallowing
  • weakness in the upper body
  • hearing loss
  • loss of pain or temperature sensation in the upper body
  • balance trouble or difficulty walking

Less frequent symptoms include general weakness, ringing in the ears, curvature of the spine, slower heartbeat, and abnormal breathing.

Symptoms in infants

Symptoms in infants from any type of CM may include:

  • trouble swallowing
  • irritability when eating
  • excessive drooling
  • gagging or vomiting
  • irregular breathing problems
  • stiff neck
  • developmental delays
  • trouble gaining weight
  • loss of strength in the arms

If type 2 is accompanied by excess fluid in the brain, additional signs and symptoms may include:

  • an enlarged head
  • vomiting
  • seizures
  • irritability
  • delayed development

Sometimes symptoms can develop rapidly, requiring emergency treatment.

CM occurs in all population groups, with about 1 case in every 1,000 births. It may run in families, but more research is needed to determine this.

The National Institute of Neurological Disorders and Stroke (NINDS) reports that more women than men are likely to have CM. NINDS also notes that type 2 malformations are more prevalent in people of Celtic descent.

People with CM often have other diseases, including hereditary neurological and bone abnormalities. Other related conditions that can increase the risk of CM include:

  • myelomeningocele: a type of spina bifida, or birth defect where the spinal canal and backbone don’t close before the baby is born
  • hydrocephalus: accumulation of excess fluid in your brain, often present with CM type 2
  • syringomyelia: a hole or cyst in the spinal column, called a syrinx
  • tethered cord syndrome: a neurological disorder caused when the spinal cord attaches to the bone of the spine. This can cause damage to the lower body. The risk is higher in people with myelomeningocele.
  • spinal curvature: a common condition, especially with children who have type 1 CM

CM is often diagnosed in the womb during ultrasound tests, or at birth. If you have no symptoms, your doctor may find it accidentally when you are being tested for something else. The type of CM present depends on:

  • medical history
  • symptoms
  • clinical evaluation
  • imaging tests
  • physical exam

During a physical exam, your doctor will assess functions that may be affected by CM, including:

  • balance
  • cognition
  • memory
  • motor skills
  • reflexes
  • sensation

Your doctor may also order imaging scans to help in the diagnosis. These can include X-rays, MRI scan, and CT scan. The images will help your doctor look for abnormalities in the bone structure, brain tissues, organs, and nerves.

Treatment depends on the type, severity, and symptoms. Your doctor may prescribe medications to ease pain, if CM doesn’t interfere with your daily life.

For cases where symptoms do interfere or there is damage to your nervous system, your doctor will recommend surgery. The type of surgery and number of surgeries you need depends on your condition.

For adults: Surgeons will create more space by removing a part of the skull. This relieves pressure on the spinal column. They’ll cover your brain with a patch or tissue from another part of your body.

The surgeon may use electrical current to shrink the cerebellar tonsils. It may also be necessary to remove a small part of the spinal column to create more space.

For infants and children: Infants and children with spina bifida will need surgery to reposition their spinal cord and close the opening in their back. If they have hydrocephalus, the surgeon will install a tube to drain excess fluid to relieve pressure. In some cases, they may make a small hole to improve fluid flow. Surgery is effective for relieving symptoms in children.

Surgery can help relieve symptoms, but the evidence from research is somewhat mixed on how effective treatment is. Certain symptoms tend to be more likely to improve after surgery than others. In the long-term, people who have surgery to treat CM will need frequent monitoring and retesting to check for changes in symptoms and functioning. The outcome for each case is different.

More than one surgery may be needed. Each outlook depends on your:

  • age
  • type of CM
  • overall health
  • existing conditions
  • response to treatment

Type 1: Chiari type 1 is not considered fatal. One study looked at 29 people with CM type 1 and found that 96 percent reported improvement six months after surgery. One person reported no change. All participants still felt residual symptoms after surgery. The most common symptoms felt after treatment included pain and loss of sensation. CM surgery can’t reverse existing nerve damage, but treatment helps prevent further damage.

CM and syringomyleia: A 2009 review study followed up on 157 cases of CM-related syringomyelia. It found a 90 percent chance of long-term improvement or stabilization.

Each outcome depends on the person. Talk to your doctor about your condition, operation risks, and other concerns. It may help to define success, which can vary from improving symptoms to eliminating symptoms.

Pregnant women can avoid some of the possible causes of CM by getting proper nutrients, especially folic acid, and avoiding exposure to hazardous substances, illegal drugs, and alcohol.

The cause of CM is the subject of ongoing research. Currently, researchers are looking at genetic factors and risks for developing this disorder. They’re also looking at alternative surgeries that may help fluid flow in children.

For more information on CM, you can visit Chiari & Syringomyelia Foundation or American Syringomyelia & Chiari Alliance Project. You can also read personal perspectives and stories about people with this condition at Conquer Chiari.