A Chiari malformation is a developmental abnormality of the nervous system that patients are born with. This occurs when the bottom portion of the cerebellum called the cerebellar tonsils protrudes from the skull into the upper spinal canal, causing crowding of the cerebellum, brainstem and spinal cord at this site. This can be seen on the MRI scan below.
Figure 1. The cerebellum (cbllm) is indicated and the tonsils (t) are shown extending below the red line that depicts the border of the foramen magnum.
When the flow of spinal fluid is obstructed, headaches can occur. The pain is usually experienced in the occipital area and the upper neck. There may be associated nausea and dizziness. Some patients may progress to have symptoms that include difficulties with swallowing, choking, and double vision. An associated condition called syringomyelia can sometimes develop. This is a cyst that forms in the center of the spinal cord.
Figure 2. The syringomyelia appears on the MRI as a cyst of varying dimension extending down the center of the spinal cord (depicted by an X) .
Syringomyelia can cause symptoms in the arms including pain, numbness, tingling, weakness, and loss of temperature sensation. Some patients with this condition may experience burns on their hands because they cannot appreciate temperature of objects they touch.
Patients are born with Chiari malformations but often do not experience symptoms until middle age or sometimes even later.
Is Treatment Necessary?
Not every patient with Chiari malformation needs to have surgery. The decision is based on whether the condition is genuinely giving rise to symptoms. It is important to discuss with patients that there can be many causes of headaches, and finding a Chiari malformation on imaging studies does not necessarily mean that this is the cause of the headache. Surgery in such cases would not be helpful for headaches due to other causes.
You will need to have a careful history and neurological examination by your neurosurgeon to determine if you have symptoms or signs of your Chiari malformation.
Surgery for Chiari Malformation
The surgical treatment involves making an incision over the back of the head and upper neck. The occipital bone behind the foramen magnum is removed to make a decompressive window, and usually the arch of the C1 vertebra needs to be removed. This is done with a drill and some special instruments. Under the operating microscope. the thick membrane over the brain called the dura mater is opened. It always has an associated thick connective tissue band that is part of the Chiari malformation that needs to be resected to relieve the crowding of the hindbrain structures. The cerebellar tonsils can be visualized.
Figure 3. The dura is opened, and both of the low-lying cerebellar tonsils are visualized at the C1 level (t).
The cerebellar tonsils can be carefully freed of any thickened arachnoidal membrane attachments, and the spinal fluid channels and the opening to the fourth ventricle of the brain opened.
A connective tissue patch is sewn in to make the membrane over the low hanging tonsils larger.
Figure 4. In order to enlarge the dura, a patch of connective tissue material is used. After it is appropriately trimmed to size, it is meticulously sewn in place in a watertight fashion to prevent cerebrospinal fluid leakage.
It is crucial to ensure that this suture line is watertight. This can take some time. If leakage occurs after surgery, another operation would usually be necessary to repair it.
Often, the Chiari decompression surgery will be effective in preventing syringomyelia, if present, from progressing and worsening. If not, sometimes a later operation may be necessary on the spinal cord to place a very small shunt tube in the syrinx and allow it to drain into the fluid-filled space around the spinal cord.
Post-operatively patients will experience some incisional pain for several days. Patients are allowed to get up and walk the next day and generally require only 2 or 3 nights in the hospital.
Recently, Dr. Stechison was interviewed as part of a Fox 5 Atlanta News story about a patient with Chiari Malformation.