Health Library

Chiari Malformation

What Causes a Chiari Malformation?

Doctors are not sure what causes Chiari malformations. The defect begins before birth when the base of a baby’s skull does not grow to a normal size. After birth, the skull hardens as the brain grows. This creates a mismatch between the skull size and brain size. As a result, the child’s brainstem, cerebellum and cerebellar tonsils become crowded.

Over time, the cerebellar tonsils (and sometimes the brain stem) get pushed down into the spinal canal. This blocks the flow of cerebrospinal fluid and causes symptoms.

In rare cases, a Chiari malformation occurs later in life to a child whose skull grew normally before birth. This is called acquired or secondary Chiari malformation. Causes can include an injury, exposure to a harmful substance or an infection.

Types of Chiari Malformations

There are four types of Chiari malformations. Chiari I and II are the most common types. Chiari III and IV are extremely rare.

Chiari I

Chiari I occurs when a portion of the brain called the cerebellar tonsils extends out of the skull and into the upper part of the spinal canal. This can disrupt the flow of cerebrospinal fluid. It is a little bit like what happens when a rock is sitting in the middle of a stream.

Chiari I can cause symptoms in infancy. Symptoms sometimes do not occur until late childhood or early adulthood, if at all. This condition often is diagnosed when a person has imaging tests for unrelated reasons.

Chiari II

Chiari II occurs when the cerebellar tonsils and the brain stem push down through the base of the skull into the upper spinal canal. Chiari II is often called Arnold-Chiari malformation. It is present at birth. Typically, it is seen in infants with myelomeningocele (a form of spina bifida) and/or hydrocephalus (a buildup of cerebrospinal fluid in the brain). It is the most common type of Chiari malformation. Almost all children with a myelomeningocele have Chiari II malformation.

Chiari III and IV

Chiari III and IV are very rare and may be life-threatening. Please talk to your child’s physician for more information about these diagnoses.

What are the Symptoms of Chiari Malformations?

A variety of problems can occur with Chiari malformations. Symptoms vary for each child.

Chiari I Symptoms

The main symptom with Chiari I is a headache in the back of the brain. The headache can be severe. Other problems can include:

• Dizziness and balance problems
• Double or blurred vision
• Numbness
• Spontaneous gagging and vomiting
• Sensitivity to bright lights

In rare cases, a child will experience sleep apnea. This is a condition in which breathing pauses during sleep.

Diagnosing Chiari I in an infant is challenging. Symptoms are not always obvious. Also, the child is not able to communicate exactly what is wrong. Common signs can include irritability, head banging and nighttime wakening.

About half of patients with a Chiari I malformation also develop a syrinx, which is sometimes called a syringomyelia or hydromyelia. A syrinx is a fluid-filled cavity in the spinal cord. It occurs when the normal flow of cerebrospinal fluid is obstructed.

A syrinx expands over time. It can injure nerve fibers in the spinal cord. It eventually can cause symptoms such as:

• Muscle weakness in the extremities
• Muscle stiffness
• Reduced ability to feel pain or temperature
• Chronic pain
• Loss of bladder and bowel control
• Numbness and tingling
• Clumsiness

Chiari II Symptoms

Chiari II is most often seen in infants with myelomeningocele, a form of spina bifida. Symptoms can include swallowing problems and slow or noisy breathing. The condition can lead to feeding problems, gagging, drooling and vomiting.

Conditions Associated with a Chiari Malformation

Children with a Chiari malformation sometimes have associated conditions. For this reason, it is important that they receive care from a multidisciplinary team of physicians. Team members may include doctors who specialize in pediatric neurosurgery, neurology, disorders of the ear, nose and throat, and other areas of medicine.

Conditions Associated with Chiari I

Patients with Chiari I may develop a syrinx, scoliosis, and/or have a tethered spinal cord.

• A syrinx is a fluid-filled cavity in the spinal cord. It can lead to a number of neurological problems. These include muscle stiffness, weakness and pain. Surgeons typically do not operate to correct the syrinx. But surgery to correct the Chiari malformation may relieve these symptoms.
• A syrinx can cause scoliosis, an abnormal curvature of the spine. For some children, treating the Chiari malformation can alter the progression of scoliosis. In other cases, children may need additional surgery to treat the scoliosis itself.
• In rare cases, a child with a Chiari malformation may have a tethered spinal cord. This means that their spinal cord is abnormally attached to tissues around the spine. A child may need surgery to correct the tethered cord, in addition to treatment for the Chiari malformation.

Children with Ehlers-Danlos syndrome (EDS) may be at increased risk for Chiari I malformation. EDS is a connective tissue disorder that causes hypermobility and unstable joints.

Conditions Associated with Chiari II

Two serious conditions associated with Chiari II are myelomeningocele and hydrocephalus. A multidisciplinary team can help diagnose and treat these conditions.

• Myelomeningocele is a severe form of spina bifida. It occurs when part of the spinal cord and surrounding nerves stick out from an opening in the spine. Children with this condition sometimes have other medical problems. These can include hydrocephalus and heart defects.
• Hydrocephalus is a buildup of cerebrospinal fluid in the brain and spinal cord.

In addition, some children with Chiari I or II have some form of sleep apnea. This is a condition in which they stop breathing temporarily during sleep. Treating the Chiari malformation may stop or lessen the sleep apnea.

How is a Chiari Malformation Diagnosed?

A magnetic resonance imaging (MRI) test is the best way to detect a Chiari malformation. An MRI can create three-dimensional images of the brain and upper spinal cord from many angles. This helps doctors make an accurate diagnosis.

MRIs also can help physicians see whether the child has a syrinx within the spinal cord or a tethered spinal cord. Follow-up MRIs can help the medical team see whether the Chiari malformation changes or worsens over time.

Once the medical team establishes a diagnosis of Chiari malformation, other tests can be used to help evaluate the child’s condition. These include:

• Computed tomography (CT) scan. This test can show blockage in the spinal canal.
• Ultrasound scan. This test can evaluate motion of the cerebellar tonsils during surgery.
• Evoked potentials. These electrical tests can determine whether the brainstem is functioning properly. They also can give information about peripheral nerves, the spinal cord and brain function.
• A swallowing test. This test can show how well the child is able to drink liquids or swallow thickened food. It is helpful for children who experience gagging or excessive drooling.
• A sleep study. This study can look at a child’s breathing pattern and determine whether enough oxygen is getting to the brain during sleep. This test is helpful for children who have a history of noisy sleeping or snoring.

How is a Chiari Malformation Treated?

Treatment for Chiari I and II varies depending on many factors. These include the exact type of malformation, the progression of the structural defect and the child’s symptoms.

If your child has a syrinx in the spinal cord, the team will recommend decompression surgery. The purpose of this surgery is to relieve pressure on the brain and spinal cord.

Rarely, the medical team may recommend surgery to place a shunt. A shunt is a tube that can help establish a normal flow of cerebrospinal fluid around and behind the cerebellum.

Chiari I Treatment

If your child has Chiari I but does not have a syrinx or symptoms, no treatment is necessary. The medical team will perform follow-up MRI scans to monitor your child’s condition. If the malformation is causing neck pain or headache, pain-relief medication may help. If your child is experiencing swallowing issues, speech therapy may be helpful.

If the pain is severe, or your child is experiencing other symptoms that affect their quality of life, the medical team may recommend decompression surgery to relieve symptoms. Without surgery, a child will likely continue to have symptoms, which may worsen over time.

Chiari II Treatment

Children with Chiari II typically do not undergo surgery, unless the malformation is causing breathing and swallowing difficulties. In that case, the medical team may recommend decompression surgery.

Long-term Outlook for Children with a Chiari Malformation

Some children never require treatment for a Chiari malformation. Others are able to enjoy a good quality of life with the help of non-surgical therapies. These therapies may include pain-relief medicine or physical therapy.

When surgery is needed, results are often very positive. Many children are symptom-free or have significantly fewer symptoms. Follow-up care includes performing MRIs at regular intervals. These tests help doctors evaluate the results of the decompression, the response of any associated syrinx, and any scar tissue development.

In a small number of cases, a second decompression surgery may be needed.