Chiari Malformation


What is Chiari malformation?

Chiari malformation is a condition in which brain tissue in the lower back part of your skull is forced into the spinal canal. Most of the time, this happens because of a structural problem –- a misshaped or smaller-than-normal part of the skull. Because there is not enough room in the skull, part of the brain, specifically the cerebellum, grows downward into the spinal canal. This can cause compression on the brain at the base of your skull. Brain tissue in the spinal canal can block the flow of cerebrospinal fluid. This fluid cushions the brain and spinal cord, circulates nutrients and chemicals and removes waste products.

Where is the cerebellum?

The cerebellum and the brain stem share a close space within the lower back portion of the skull. They reside above an opening at the base of the skull –- called the foramen magnum –- through which the spinal cord passes. A Chiari malformation occurs when the cerebellum is forced downward below the foramen magnum and into the spinal canal. The cerebellum controls your muscle movements, posture, balance, speech and coordination.

In the normal brain, your cerebellum and its tonsil remain inside your skull and the spinal canal is unblocked, allowing spinal fluid to flow.

In the normal brain, your cerebellum and its tonsil remain inside your skull and the spinal canal is unblocked, allowing spinal fluid to flow.

Who does Chiari malformation affect?

Chiari malformation can affect anyone. Females have a slightly higher chance of having a Chiari malformation than males.

In most cases, babies are born with the condition. However, sometimes Chiari malformations aren’t discovered until the teen years or adulthood when a brain scan is ordered for another reason. Although there is no cure for Chiari malformation, surgeons can treat or manage symptoms in most people.

How common is Chiari malformation?

Chiari malformation occurs in about one out of every 1,000 people. Because some people don’t have any symptoms or don’t show them until adolescence or adulthood, the condition may actually be more common.

Are there different types of Chiari malformation?

There are several types of Chiari malformations that are distinct entities from each other but share some similarities. Doctors categorize the disorder based on anatomical findings and associated conditions. The main types are:

  • Chiari malformation type I: People with type I may not have any symptoms or they may not develop symptoms until they are adolescents or adults. Type I occurs when the lower part of the cerebellum extends into the hole (the foramen magnum) at the base of the skull. The spinal cord normally passes through this hole. Type I is the most common form of Chiari malformation.
  • Chiari malformation type II: Type II is part of a complex malformation that occurs during brain and spine development in utero. Type II is most commonly found in patients with the most severe form of spina bifida called myelomeningocele. Myelomeningocele occurs when the backbone and spinal canal don’t close properly before the baby is born. Surgery is required to close the spine after birth, and paralysis can occur below the area where the spine is malformed. With type II malformation, there is often both cerebellum and brain stem herniation into the spinal canal, along with other additional brain abnormalities. People with type II may require surgery to treat the other associated conditions, but only require treatment of the Chiari type II if they have symptoms.
  • Chiari malformation type III: This is a rare and most severe of the Chiari malformations. It occurs when some of the cerebellum and brain stem extend through an abnormal opening in the back of the skull (not the foramen magnum). In addition, some of the membranes that surround the brain or spinal cord extend through the opening. This malformation results in a swelling at the back of the skull called an encephalocele. Type III causes severe, life-threatening symptoms and they appear early in life. Children with type III have neurological problems, learning delays and seizures. These often require surgery.

Some scientists classify two other types -- type IV and type 0. Type IV is a rare type and happens when the cerebellum itself is underdeveloped or has parts missing. Parts of the skull and spinal cord may be visible. This type is severe and usually fatal in infants.

Type 0 is a very rare entity. In this type, there is little or no extension of parts of the cerebellum into the foramen magnum but there is significant crowding at that level. Symptoms are thought to be caused by abnormal flow of cerebrospinal fluid at the base of the skull.

Symptoms and Causes

What causes Chiari malformation?

Chiari malformation has multiple causes. Chiari malformation is caused by a structural defect in the brain and spinal cord that happens while a baby is developing in the uterus. Some investigators also believe that the structural defect in the skull (smaller than normal size in the area where the cerebellum sits) leads to the crowding and pressure on the brain that pushes it through the foramen magnum where the brain and spinal cord meets.

Because Chiari malformations have occurred in more than one family member, the disorder might also be inherited (passed down through families) in some cases.

Some researchers believe a lack of certain nutrients during pregnancy may play a role.

Chiari malformations are almost always present at birth, though symptoms may not develop until later in life. Very rarely, a Chiari malformation can develop in someone who was not born with the disorder. In these cases, the skull or spinal cord might change shape due to tumors, irregularities of the spine or hematomas.

What are the symptoms of Chiari malformation?

Symptoms vary from person to person and range from no symptoms to mild to severe symptoms. In some people, symptoms are present at birth. In others, symptoms appear in late childhood or adulthood. Symptoms may also get better or worse at different points in time. Common symptoms include:

  • Headache pain: This is the most common symptom. Headache can start or worsen after coughing, sneezing or straining and often occur at the back of head. Pain may spread to the neck and shoulder. Pain is described as throbbing, stabbing or sharp.
  • Balance and movement problems: Muscle weakness, coordination issues and numbness in the limbs can lead to problems with fine motor skills. Chiari malformation can also cause dizziness, vertigo and balance problems.
  • Problems with hearing and vision: Some people hear a buzzing or ringing sound (tinnitus) and may have trouble hearing. Double vision (diplopia), blurred vision, abnormal eye movements (nystagmus) and sensitivity to light (photophobia) can also occur.
  • Trouble with eating, drinking and speaking: Swallowing problems (dysphagia) can occur. Babies with Chiari malformation may vomit, gag or drool a lot. They may have trouble eating, and they may not be able to gain enough weight to develop properly.
  • Scoliosis: The spine can become curved, a condition called scoliosis.
  • Difficulty sleeping: Insomnia can occur, sometimes due to pain from headaches. Some people also experience sleep apnea (trouble breathing while sleeping).
  • Bladder and bowel issues: Loss of control over the bladder and bowel can result from Chiari malformation.
  • Other symptoms: Other symptoms include chronic fatigue, palpitations, fainting episodes and tingling or burning sensations in fingers, toes or lips.

What are the complications of Chiari malformation?

Chiari malformation can cause severe health problems and developmental delays. Complications include:

  • Hydrocephalus: This life-threatening condition occurs when cerebrospinal fluid (CSF) builds up in the brain. Hydrocephalus happens when the CSF can’t drain. As CSF builds up, it causes pressure within the head and can result in mental disabilities and/or a misshaped skull. It can be fatal if not treated. A flexible tube (a shunt) may be placed to drain the CSF. This complication is most often seen in Chiari malformation type II.
  • Syringomyelia and Hydromyelia: When CSF is not flowing properly at the junction between the brain and the spine, some CSF can accumulate in the spine. This fluid build up can cause damage to the spinal cord and causes a variety of health issues. These problems can include movement and balance problems, pain, muscle weakness, muscle spasms and contractions, numbness/decreased sensation to hot and cold, and loss of bladder and bowel control.
  • Tethered cord syndrome: People with chiari malformations may have associated spinal conditions such as spina bifida. In some forms, there may be an abnormal attachment of the spinal cord to the spine that causes tension on the nerves with growth and movement. Additionally, children born with myelomeningocele (a severe form of spina bifida) are at increased risk for developing tethered cord syndrome as they grow. This occurs when the spinal cord becomes attached to the spine due to scarring from the original closure surgery. With tethered cord syndrome, there can be slow and progressive nerve damage that affect the muscles of the lower body and legs, and bowel and bladder function.

Diagnosis and Tests

How is Chiari malformation diagnosed?

Sometimes, Chiari malformations appear on prenatal ultrasounds before a baby is born. An ultrasound is an imaging test that uses sound waves to produce pictures of soft tissues.

To diagnose Chiari malformation, doctors perform a complete physical exam. Your doctor will test your movement, balance and sensation in your hands and feet. Doctors also check for memory problems, learning issues and cognitive delays. To see a detailed image of the brain and spinal cord, your doctor may order:

  • Magnetic resonance imaging (MRI): This imaging test can show soft tissues and bones. It can evaluate the brain, spinal cord and cerebrospinal fluid. MRI can show the extent that the cerebellum is extending into the spinal canal.
  • Cine MRI: This test is similar to a traditional MRI, but it allows your doctor to see the flow pattern of cerebrospinal fluid (CSF) around the base of the skull.
  • Computed tomography (CT): A CT scan helps detect problems in bones at the base of the skull and the spinal column.
  • X-ray: Doctors use X-rays to check for bone abnormalities in the skull and neck.

Management and Treatment

How is Chiari malformation treated?

Your doctor will make a treatment plan based on the severity of symptoms. If symptoms are mild, your doctor will monitor your health with regular MRIs.

More severe cases may need surgery. Surgical procedures to treat Chiari malformation include:

  • Posterior fossa decompression: This is the most common procedure to treat Chiari malformation. A surgeon relieves pressure on the brain, giving it more room, by removing a part of the back of the skull called the posterior fossa.
  • Laminectomy: Depending on how severe the Chiari malformation is, the surgeon may also need to remove a small portion of bones covering the spinal column to restore the flow of cerebrospinal fluid and allow more room for the spinal cord.
  • Duraplasty: In this decompression surgery, the surgeon opens the dura (a membrane on the outside of brain). Then the surgeon sews in a patch to make the membrane larger so the brain has more room. This procedure enlarges the area and relieves pressure on the brain.
  • Electrocautery: To create more room and allow the cerebrospinal fluid (CSF) to drain, surgeons may apply a small amount of electricity to shrink a small part of the brain called the cerebellar tonsils. The cerebellar tonsils retract without causing neurologic damage.


Can you prevent Chiari malformation?

Chiari malformation usually develops while the infant is in the uterus. It is created due to a genetic mutation. It can’t be prevented. Sometimes Chiari malformation occurs along with spina bifida. If you’re pregnant or plan to become pregnant, you may be able to lower the risk of having a baby with spina bifida by taking folic acid. Talk to your doctor before taking folic acid or other supplements.

Outlook / Prognosis

What is the outlook for people with Chiari malformation?

The outlook varies depending on the severity and type of Chiari malformation. Some people live their entire lives with Chiari malformation and experience mild symptoms or none at all. Other people with Chiari malformation have severe disabilities. It’s important to work closely with doctors and surgeons who can monitor your symptoms and determine the right treatment plan for you.

Last reviewed by a Cleveland Clinic medical professional on 10/20/2020.


  • National Organization for Rare Disorders. Chiari Malformations. ( Accessed 10/10/2020.
  • American Association of Neurological Surgeons. Chiari Malformation. ( Accessed 10/10/2020.
  • National Institutes of Health. National Center for Advancing Translational Sciences. Chiari malformation type 1. ( Accessed 10/10/2020.
  • National Institute of Health. National Institute of Neurological Disorders and Stroke. Chiari Malformation Fact Sheet. ( Accessed 10/10/2020.

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