Brain, Spinal Cord and Nerve Conditions and Diagnoses

Chiari Malformation

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Explanation | Symptoms | How Diagnosed | Surgery Options

What is Chiari malformation?

A Chiari malformation is a condition in which the back of the brain (cerebellum) extends down into the upper spinal canal. Children are usually born with this malformation, but it also can develop later in childhood. There are four types of Chiari malformations:

Chiari I malformation is the most common type
Chiari II, commonly referred to as the Arnold-Chiari Malformation, is found almost exclusively in children with spina bifida
Chiari type III and IV malformations are extremely rare
References to a Chiari 0 malformation may be found but all physicians who treat Chiari malformations have not accepted this name

Why Chiari malformations develop is unclear, but since the use of magnetic resonance (MR) imaging, more children have been diagnosed with this condition. It is believed that the portion of the skull containing the cerebellum is smaller and results in crowding of the brain and possibly the spinal cord. In many instances a fluid collection may be present in the spinal cord as a result of the Chiari malformation. This fluid collection is known as a syrinx and may be seen on the MR scan.

Symptoms

A Chiari Malformation may cause a variety of symptoms. In infants and young children, difficulty with feeding and swallowing are more common and may result in gagging, drooling and vomiting. Abnormal breathing may occur resulting in the child having slow or noisy breathing similar to snoring in adults. Irritability, head banging and nighttime awakening may all be signs of headache in young infants. Symptoms in older children commonly include headache, spinal curvature, clumsiness and in rare cases difficulty controlling bladder function.

How are Chiari malformations diagnosed?

An MR scan is the best way to diagnose a Chiari malformation. The brain and upper spinal cord can be seen from many angles, which permit an accurate diagnosis to be made. Additional tests may be also performed to help in evaluating patients with Chiari malformations:

An MR scan of the entire spine may be done to see if the spinal cord is too low in the spinal canal. This problem is known as a tethered cord and is found in a small number of patients with a Chiari malformation.
A swallowing test may be done to see how a patient is able to drink liquids or swallow thickened food. This test may help to explain problems when patients have gagging or excessive drooling.
In patients who have a history of noisy sleeping or snoring, a sleep study is performed to evaluate the breathing pattern and determine if enough oxygen is getting to the brain during sleep.

Sometimes children have a Chiari malformation diagnosed by an MR scan but have no symptoms. These children will seldom require surgery. A follow-up MR scan maybe recommended to see if the Chiari malformation changes.

Surgery for Chiari I Malformations

For children experiencing symptoms and who have been diagnosed with a Chiari malformation, the treatment is surgery in order to create more space for the brain and spinal cord. Without surgery, symptoms would be expected to continue or even worsen over time.

The goal of surgery is increase the amount of space at the base of the brain. A small portion of bone at the bottom of the skull must be removed to create this extra space. The bone that is removed will not be put back but the muscle and skin covering this bone is thick enough to provide protection to the brain.

A small incision or cut is made in the skin in the back of the head. The cut is about four inches in length. The muscles that cover the bone at the bottom of the skull are gently moved out of the way. Small drills are used to cut the bone away from the skull. After this bone is removed, the neurosurgeon may use an ultrasound machine to see if enough space has been made. If enough space is present, the surgery is complete and the incision is sewn closed.

If more space is needed, an opening must be made in the thick covering of the brain. The covering is called the dura mater. Most neurosurgeons then sew a patch of material over this opening to keep spinal fluid from running out of the back of the head. Opening the dura mater and sewing in this patch makes all the space that is needed. In addition, some neurosurgeons will shrink the part of the brain tonsils that are crowding into the upper spinal canal. These brain tonsils do not have any function so it is safe to shrink this brain tissue.

Children who have surgery have a very good chance of being helped by the surgery. The neurosurgeons at Cincinnati Children's Hospital Medical Center have performed surgery on 250 children with Chiari malformations. All children need follow-up visits to make certain the symptoms do not return.