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What is Chiari malformation?

Chiari malformation is an abnormality in the back of the head where the brain and spinal cord meet. It causes some of the brain tissue at the base of the skull to be pushed into the spinal canal. This can cause pressure on the brain and block the normal flow of spinal fluid in and around the brain. Sometimes this leads to a buildup of spinal fluid within the spinal cord, called a syrinx.

What are the types of Chiari malformation?

There are four types of Chiari malformation. They are categorized by which parts of the brain are pushed into the spine and the severity of the condition:

  • Chiari malformation type I is the most common. It’s the only type that can also develop after birth. People with type I often have no symptoms and need no treatment.
  • Chiari malformation type II almost always affects children who have spina bifida and develops before birth. Most children with type II Chiari malformation need surgery.
  • Chiari malformation type III is very serious, but rare. In this type, some parts of the brain may protrude from the skull. It usually causes severe disabilities.
  • Chiari malformation type IV is also very serious and very rare. In this type of Chiari malformation, part of the brain is not developed or is missing.

Because type III and type IV Chiari malformations are so rare, we will focus only on type I and type II on this website.

Chiari Malformation | Symptoms & Causes

What are the symptoms of type I Chiari malformation?

Children with type I Chiari malformations often have no signs or symptoms. In many cases, they are diagnosed after having a magnetic resonance imaging (MRI) scan for another problem.

When symptoms do occur, they most often start in the teen years or early adulthood. These may include:

  • headaches, especially when coughing, sneezing, or straining
  • neck pain
  • balance problems
  • dizziness
  • trouble swallowing
  • numbness or tingling in the arms or legs
  • vision problems
  • breathing problems, especially during sleep
  • loss of bowel or bladder control
  • a curve of the spine, called scoliosis

What are the symptoms of type II Chiari malformation?

Children with type II Chiari malformations are more likely to have symptoms. These may include:

  • a build-up of fluid in the brain (hydrocephalus)
  • a weak cry
  • trouble swallowing
  • breathing problems
  • problems with nerve function in the throat and tongue

What are the causes of Chiari malformation?

  • Type I: This type occurs if the skull is too small or if the brain grows more quickly than the skull, causing the bottom of the brain to push into the spinal canal.
  • Type II: Almost all children with a type II malformation have a form of spina bifida called myelomeningocele, when the backbone and spinal canal don’t close before birth.

Chiari Malformation | Diagnosis & Treatments

How is Chiari malformation diagnosed?

The doctor will examine your child and ask about his or her symptoms and medical history. To help diagnose Chiari malformation, your child’s doctor may also use one or more of the following tests:

How is Chiari malformation treated?

Many children with type I Chiari malformation do not need treatment. If your child has no symptoms, your doctor will likely recommend watching the condition with exams and MRIs.

If your child has symptoms, they will likely need surgery to relieve pressure on the brain and spinal cord and to restore the normal flow of spinal fluid in the area. The type of surgery your child’s doctor recommends will depend on the type of Chiari malformation your child has and his or her age and symptoms.

What is brain decompression surgery?

The most common surgery for Chiari malformation is posterior fossa decompression. During this surgery, the surgeon removes a bit of bone from the lowest part of your child's skull. This helps relieve pressure and reduces symptoms. The surgeon may also use an electrical current to shrink some of the tissue.

Are there other types of surgery for Chiari malformation?

Children with type II Chiari malformation may need surgery to close the opening in the back of the skull and to move the position of the spinal cord.

If your child has other conditions related to the Chiari malformation, such as hydrocephalus, he or she may need a different type of surgery or a shunt (a thin tube) to drain extra fluid out of the brain.

What is the long-term outlook for Chiari malformation?

In most cases, the surgery relieves symptoms completely or reduces symptoms. In some cases, children with Chiari malformation may need more than one surgery.

How we care for Chiari malformation

At Boston Children’s Hospital, our team of experts in the Department of Neurosurgery has years of experience helping infants, children, and teens who have been diagnosed with a Chiari malformation.

Chiari Malformation | Programs & Services