Brain, Nervous System and Mental Conditions

Chiari Malformation

What Is a Chiari Malformation?

Chiari malformation

An MRI of a child with a Chiari I malformation. The white line shows where the large hole in the base of the skull (foramen magnum) is. The arrow shows the bottom parts of the cerebellum (cerebellar tonsils) pushing down 10 millimeters into the cervical spinal canal. Photo courtesy of the Chiari and Syringomyelia Foundation.

A Chiari malformation (pronounced key-AR-ee mal-for-MAY-shun) is a problem with the way parts of the brain are shaped and the way they sit in the skull.

In children who have a Chiari malformation, the cerebellum and sometimes the brainstem and the brain's fourth ventricle come down through the large hole in the base of the skull (foramen magnum) into the upper neck. They squeeze into the space where the spinal cord enters the first one or two bones of the spine (cervical spinal canal).

Crowding in the cervical spinal canal may limit the flow of cerebrospinal fluid (CSF). It also may put pressure on the brain and spinal cord.

Types of Chiari Malformations

There are four types of Chiari malformations. We discuss only types I and II here because they are much more common than types III and IV. Types III and IV are very rare.

  • In a Chiari I malformation, the bottom parts of the cerebellum (cerebellar tonsils) come down into the cervical spinal canal. The cerebellum affects balance and coordination.
  • In a Chiari II malformation, the cerebellar tonsils, the lower part of the brainstem and the fourth ventricle come down into the cervical spinal canal. The brainstem connects the brain with the spinal cord.

Chiari Malformation in Children

Often a Chiari malformation is present when a child is born (congenital), but it may happen after birth, too.

Sometimes doctors and families do not know a child has a Chiari I malformation until later in life because the child has no symptoms. Some people don't learn that they have this condition until they are adults. For this reason, Chiari I malformation is sometimes called adult Chiari. Most people with a Chiari I malformation are not born with any other health problems.

Chiari II malformations happen most often in children who have spina bifida or myelomeningocele and sometimes in children who have hydrocephalus. Some children have a Chiari II malformation, myelomeningocele and hydrocephalus. Together, these three conditions form a complex birth defect.

Reasons for Chiari Malformations

Chiari malformations can happen for many reasons. Usually they happen because the back of the child's skull is too small for the child's growing brain. Less often, the skull bones are not the normal shape or at the normal angle (malformed). Other conditions that can affect the brain, such as brain tumors, can also cause Chiari malformations. Each of these conditions can prevent the brain from fitting into the skull, causing brain tissue to "escape" through the foramen magnum.

Rarely, children with a Chiari malformation have a tethered spinal cord - their spinal cord is pulled down and stuck in their spinal canal. This might play a role in their brain being pulled down into their cervical spinal canal. They may need treatment for their tethered cord before their Chiari malformation is treated.


Children with a Chiari I or II malformation may have a cyst in their spinal cord called syringomyelia (pronounced se-ringo-my-EEL-e-ah). The cyst, also called a syrinx, is filled with CSF. It may form because the normal flow of CSF is partly blocked and it's easier for CSF to collect inside the spinal cord than to flow around or seep through the blockage.


Most children with scoliosis do not have a Chiari malformation. But if a child's scoliosis doesn't act the way doctors expect - like if the scoliosis gets worse quickly or happens along with neurologic deficits - the child may have a Chiari malformation and syringomyelia. A syrinx could be causing the child's spine to curve. For some of these children, treating the Chiari malformation and syrinx may stop the scoliosis from getting worse or even improve it.

Genes and Chiari malformations

The role of genes in Chiari malformations is complex. Genes appear to play only a very small role. If you have a child with a Chiari malformation, your chance of having another child with this condition is probably no greater than anyone else's. In some families, more than one person has a Chiari malformation. These families may be at greater risk. Your child's doctor can talk with you about the risk for your family.

Chiari Malformation at Seattle Children's

Children from across the United States come to Seattle Children's for treatment of Chiari malformations. Each year our neurosurgeons perform about 40 surgeries on children with this condition. We also evaluate and follow many children with Chiari malformations who don't need surgery - either because they have no symptoms or they have mild symptoms that we can treat in other ways. In our Neurodevelopmental Clinic, we work closely with experts in many medical areas to care for children affected by Chiari malformations.


Our first step in your child's care is making an accurate diagnosis. For many children, this means having an MRI (magnetic resonance imaging) scan. Your child's doctor may also order a special MRI called a cine-MRI (or cine MRI CSF flow study). This can show how CSF moves around the lower part of your child's brain. Richard G. Ellenbogen, MD, and a team of researchers helped develop the use of cine-MRI for children with Chiari malformations.

Our approach to surgery

Another important part of your child's care is making a thoughtful decision about if they need surgery. At Seattle Children's, we take a conservative approach. We do surgery for Chiari malformations only in select children. These include children whose symptoms limit their lifestyle significantly and children with syringomyelia, scoliosis or neurologic deficits that are getting worse. For children who need surgery, we follow the most modern protocols. Our neurosurgeons monitor many children who have not had surgery so we can detect whether surgery becomes the right choice for them at some point.

When you come to Seattle Children's, your child's team will carefully diagnose your child's condition. Then we will work with you to decide whether surgery, some other treatment or regular check-ups are best for your child.


Dr. Richard Ellenbogen studies the best surgical treatments for Chiari I malformation and the results of surgery for patients. He is also involved in research using magnetic resonance imaging (MRI) to better understand how the flow of cerebrospinal fluid (CSF) around the brain and spinal cord affects people with syringomyelia. Ellenbogen has treated more than 1,000 patients with Chiari malformation or syringomyelia, and he serves on the scientific, education and advisory board of the Chiari & Syringomyelia Foundation.

Seattle Children’s doctors and scientists are also leading research to discover the genetic causes of Chiari malformation so we can use current treatments more effectively and develop new, better therapies.