Chiari malformation

At Boston Children’s Hospital, we understand that a diagnosis of a brain abnormality such as Chiari malformation comes with many questions and concerns for parents and families. We’ve provided straightforward information about Chiari malformation here, and when you meet with our team of doctors, they’ll be able to explain your child’s condition and options fully. Learning more about your child’s diagnosis and treatment options is a great way to become an active participant in his medical management.

What is the difference between type I Chiari malformation and type II Chiari malformation?

Type I and Type II Chiari malformation both cause brain tissue to protrude into the space at the back of the skull.  However, there are a few differences that distinguish these two conditions:

• Type I Chiari malformation occurs because of a developmental abnormality and it can affect any child.  Type I involves the lower part of the cerebellum (also known as the “tonsils”).

• Type II Chiari malformation is specific to children that have spina bifida, a congenital defect that occurs when a baby is born with an open and unprotected spinal cord at the bottom of the spine. Type II involves a greater amount of brain tissue than type I.

Causes

What causes Chiari malformation?

The causes of type I and type II Chiari malformations are different.

Type I

• In the past, it was thought that type I Chiari malformation was congenital, meaning that a child was born with the abnormality. As MRI imaging became more commonplace, doctors saw that the malformation actually develops due to a mismatch between the rate of growth of the skull and the rate of growth of the brain, causing the bottom of the cerebellum to push out of the base of the skull into the spinal canal over time. 

• Researchers have also observed links to genetics and developmental syndromes.

Type II

• Almost all children with type II malformations have spina bifida.  As a result, many of these children require treatment for hydrocephalus (build-up of fluid in the brain).

Signs and symptoms

What are the symptoms of Chiari malformation?

The symptoms of type I Chiari malformation and type II Chiari malformation are different.

Type I:

• The symptoms of type I Chiari malformation and their degree of severity vary from person to person. In most cases, individuals with type I Chiari are asymptomatic and don’t even know that they have it. But if the malformation is severe, the following symptoms may occur:

• One of the primary symptoms of type I Chiari malformation is pain in the lower back of the head into the neck (also known as suboccipital pain). This is a headache that tends to come on quickly and is made worse by any activity that increases pressure in the brain, such as coughing and sneezing.

• In some cases, the cerebellar tissue can extend down low enough into the spinal canal that it blocks the normal flow of cerebral spinal fluid (CSF) or puts too much pressure on the brain or spinal cord. This can affect the child’s nervous system and cause symptoms such as dizziness and problems with balance and coordination.

• Chiari I can also cause fluid to build-up in the spinal cord (syringomyelia), which may lead to scoliosis. The reason for this is still unknown, but many doctors believe that it’s because the fluid gets blocked by the malformation and then collects in the spinal cord. The harmful pressure of the fluid’s pressure on the nerve cells weakens the muscles and leads to a curvature of the spine. Untreated, it can lead to other neurological deficits.

Other symptoms of type I can include:

• Swallowing difficulties

• Sleep apnea

• Rarely, but occasionally, cough syncope can occur. Children who experience a cough syncope lose consciousness for a brief period of time and pass out after coughing or sneezing.

Type II:

Build-up of fluid in the brain (hydrocephalus) occurs in the majority of children with type II Chiari malformation. Older children may notice head pain with a cough or a sneeze, bending over, strenuous physical activities, or straining to have a bowel movement.

More frequently, children with type II Chiari malformation have problems with the function of the nerves in the brain stem, such as:

• Weakness of vocal cords
• Swallowing difficulties
• Breathing irregularities
• Serious changes in the function of nerves of the throat and tongue