Children's Hospital Colorado

Chiari Malformation

What is Chiari malformation (CMI)?

A Chiari malformation is an abnormal connection between the bottom of the brain and the spinal column. In the most common type of Chiari malformation, Type I (called CMI), the structure at the bottom of the brain, called the cerebellar tonsils, extends past the bottom of the skull and into the spinal canal. Sometimes the malformation can include more structures of the brain and is considered a more serious form of the condition.

What are the types of Chiari malformation?

There are four different types of Chiari malformation (I, II, III and IV).  Although they share some characteristics, they are very different. Type I is by far the most common in children. Ten to 20% of patients with CMI also have scoliosis, an abnormal curvature of the spine, or a syrinx, a pocket of fluid that collects in the spinal cord. These conditions often contribute to the patient's symptoms and findings during a neurological exam.

What causes Chiari malformation?

Current research indicates that CMI usually happens when the volume of the inside of the back or bottom of the skull is too small to hold all the neural tissue within it. As a result, a small portion of the bottom of the cerebellum, the back of the brain, pushes downwards into the spinal canal.

Current research does not suggest that there are any environmental or maternal risk factors that cause CMI.

Who gets Chiari malformation?

Because most children with CMI have no symptoms and do not require therapy, the exact number of patients with the condition is not known. Some sources estimate that 3% of the total population has Chiari malformation.

While no gene or gene combination has been correlated with CMI, occasionally families have more than one member with CMI. There are some genetic syndromes that include CMI, which indicates that people with some genetic profiles may be more likely to develop the condition.

What are the signs and symptoms of Chiari malformation (CMI)?

In children who have CMI, the most common symptom is headache, with or without neck pain (which occurs in 28% to 63% of patients). Typically the neck pain is severe and short-lived, and often related to coughing or straining. Less frequently, the pain is dull and persistent.

In nonverbal children, pain may manifest as persistent crying or irritability, sometimes with hyperextension of the neck or entire spine. There are many other potential symptoms, which sometimes makes diagnosis challenging. Examples include poor balance, eye movement abnormalities, swallowing problems and facial numbness. Spinal cord compression, which may result from fluid within the spinal cord, may cause pain, weakness or sensation changes. One in 5 patients may have dysfunction of nerves of the face or head. This can cause sleep apnea, difficulty speaking, hoarseness, recurrent aspiration and tongue atrophy.

In studies of children with CMI, numbness or sensation loss has been reported in 26% to 50% of patients. Partial loss of strength is present in 12% to 19% of patients, and it is considerably more common in patients who have a fluid collection within the spinal cord.

What tests are used to diagnose Chiari malformation Type 1 (CMI)?

Magnetic Resonance Imaging (MRI) – MRI is a magnetic-based test that does not involve radiation. It has allowed many children with CMI to be diagnosed before significant symptoms develop and is the best test to show the anatomy of the brain and spinal cord tissue.

Tests for a child thought to have CMI should include MRI imaging of the brain to rule out a Chiari malformation caused by a mass lesion or hydrocephalus. An MRI of the entire spine should be done to test for the possibility of a fluid collection within the spinal cord, abnormal curvature if the spine (scoliosis) or other less common abnormalities such as a tethered spinal cord.

Computed Tomography (CT) – A CT scan is an X-ray based test that shows the bone of the skull and spine in better detail than any other imaging test. It is sometimes, but not always, part of the evaluation of a patient with CMI.

X-ray – An upright spine X-ray is also used to look for abnormal curvature of the spine (scoliosis). X-rays with the patient flexing and extending the neck may be needed to evaluate movement between the bones of the neck or skull and neck.

Why choose Children's Hospital Colorado for testing?

An MRI is the best test for children with suspected CMI, and it has the advantage of being a radiation-free test. However, MRI machines are noisy and the test can last about an hour. Because of this, many children require sedation in order to remain still during the study.

Children's Colorado has anesthesia and radiology specialists who take care of children all day, every day. They have considerable experience handling the big and small details that make the imaging experience as smooth as possible for your child and family.

What should you expect from an MRI?

The longest test used to diagnose Chiari malformation is an MRI of the entire spine. Because this test can last for about an hour, younger children may need anesthesia to stay calm and still. For older children, we provide ear buds and glasses for the patient to watch movies during the study.

How do doctors at Children's Colorado diagnose Chiari malformation?

The MRI scan shows whether the back or bottom of the brain extends into the spinal canal. It can also show if there is a fluid collection in the spinal cord (syrinx) or abnormal curvature of the spine (scoliosis). We combine this information with an evaluation of your child's history and physical examination in order to determine if there is symptomatic CMI, which may require surgery.

How is Chiari malformation Type 1 treated?

In most cases, Chiari malformation Type 1 (CMI) does not require any treatment because it does not cause symptoms or pain that affect a child's life.

In the cases that do require treatment, surgery is the first option because there are no other effective medical therapies. During the procedure, a small area of bone from the skull and neck is removed. Sometimes during the surgery, doctors expand the size of the protective layers that surround the brain and spinal cord.

What to expect from surgery

The goal of surgery is to provide more space for the small portion of the brain (cerebellar tonsils) that extends into the spinal canal. This also allows for better flow of the cerebrospinal fluid at the junction of the skull and spine. This fluid is a normal an important part of the brain and nervous system.

During surgery a small portion of the bone at the back of the skull and first bone of the neck are removed. At this point, there is an option to open the outermost protective layer of the brain (called the dura mater) or to thin this layer without opening it completely in order to provide more space for important brain structures.

Opening the protective tissue layer and sewing in a patch to make the space larger is called duraplasty. The surgical procedure is called "posterior fossa decompression with or without duraplasty." The decision to perform duraplasty is tailored for each patient based on symptoms, the characteristics of the malformation seen on imaging tests, and a discussion with the patient and parents.

Why choose Children's Colorado for your child's Chiari malformation?

Children's Colorado has the largest and most experienced pediatric neurosurgical faculty in Colorado. Our team cares exclusively for children with neurosurgical problems, and we perform the most pediatric neurosurgical procedures of any hospital in a six-state region.

Our staff has extensive experience performing the corrective surgery for Chiari malformation Type 1 (CMI) and has written medical research papers regarding the procedure. We are also a member of the largest research group in the United States that is studying children with CMI.

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