Chiari Malformation

About Chiari Malformation:

Chiari (kee-AR-ee) malformation (CM) includes a complex group of disorders characterized by herniation of the cerebellum through the large opening in the base of the skull (foramen magnum) into the spinal canal. The herniated tissue blocks the circulation of cerebrospinal fluid in the brain and can lead to the formation of a cavity (syrinx) within the spinal cord. There are three main types of CM. CM1, the simplest and most prevalent form, is generally considered to be a congenital malformation, although acquired cases are recognized. (See diagrams below.) It is rarely apparent at birth. CM2 and CM3 are more severe congenital malformations that are apparent at birth and associated with complex defects of the brain and spinal cord.

Patients with CM1 may experience no symptoms. When symptoms are present, they usually do not appear until adolescence or early adulthood, but can occasionally be seen in young children. The majority of patients complain of severe headache and neck pain. Other common symptoms are dizziness, vertigo, disequilibrium, visual disturbances, ringing in the ears, difficulty swallowing, palpitations, sleep apnea, muscle weakness, impaired fine motor skills, chronic fatigue and painful tingling of the hands and feet. Because of this complex symptomatology, patients with CM1 are frequently misdiagnosed.

How common is Chiari malformation?

Until recent years, CM1 was regarded as a rare condition. With the increased availability of magnetic resonance imaging, the number of reported cases has risen sharply. Current estimates range from 200,000 to 2 million Americans with the condition. Genetic studies spearheaded by Dr. Milhorat support a hereditary tendency with a transmissibility rate of 12 percent. Women are affected three times more often than men. Approximately 3,500 Chiari operations are performed each year in the United States.

How are Chiari malformations diagnosed?

An MRI 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 MRI 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 MRI 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.  All children need follow-up visits to make certain the symptoms do not return.