Chiari Malformation
Important information:
Chiari malformation is an abnormality in the area where the brain and spinal cord meet. It causes some of the brain tissue in the lower part of the brain to be pushed through the opening at the bottom of the skull and into the spinal canal. This can put pressure on the brainstem and spinal cord, block the normal flow of spinal fluid in and around the brain, and lead to a buildup of spinal fluid within the spinal cord.
This can cause symptoms but is often found during imaging for another reason.
There are several forms of Chiari malformation. Chiari type 1 occurs in otherwise healthy individuals. Chiari type 2 occurs in patients with myelomeningocele (spina bifida).
The brain is divided into 3 major parts:
Cerebrum: Upper part, responsible for thought, memory, personality, and intelligence.
Ventricles: Fluid-filled spaces withing the cerebrum.
Cerebellum: Back part, controls balance and fine motor movements. The very bottom of this part of the brain is called the tonsil (not to be confused with the tonsils in the throat). This area has no known function in humans.
In front of the cerebellum is the brainstem, which is the central relay station that connects the brain with the rest of the body. It transmits signals that allow us to move muscles. It also carries sensations like pain and touch to the brain, where we can feel them. Spinal fluid, or CSF, drains through a passageway that is between the cerebellum and the brainstem. Once it escapes, that fluid circulates up and around the outside of the brain, where it is eventually absorbed back into the bloodstream.
Chiari malformation
Chiari malformation is when part of the cerebellum protrudes into the spinal canal:
Sometimes, the Chiari malformation can block the flow of spinal fluid from the ventricles. In these cases, the fluid can back up into the ventricles and cause hydrocephalus. More commonly, the fluid can back up and cause a cyst to form inside the spinal cord, called a syrinx, or syringomyelia.
Symptoms
A Chiari malformation can cause no symptoms at all and may be found when imaging is done for another reason. In these cases, no treatment is usually required, unless a syrinx is present.
Some patients with a Chiari can have symptoms like headaches, usually at the back of the head or neck. These headaches often get worse with straining, like when lifting, sneezing, coughing, or during a bowel movement. Other symptoms may include gagging, choking, trouble swallowing, or sleep apnea.
If a syrinx is present, it may or may not cause symptoms. A syrinx can be quite large yet remain asymptomatic. When symptoms do occur, they may include numbness, tingling, weakness, and scoliosis.
Diagnosis
A Chiari malformation is often found through brain imaging, such as a CT scan or MRI. Your child's neurosurgeon will likely suggest an MRI of the cervical and thoracic spine to assess the Chiari and check for the presence of a syrinx in the rest of the spine. Testing will also include a specialized MRI called a CSF flow study, which looks for any reduced flow or blockage of spinal fluid around the Chiari malformation.
Treatment
Management options for a Chiari malformation include observation or surgery. There are no medical non-surgical treatments available for this condition. If there are no symptoms attributed to the Chiari malformation and no syrinx is present, then typically no treatment is needed. However, your neurosurgery team may recommend yearly imaging to monitor any changes in the Chiari or the development of a syrinx, as well as to watch for any associated symptoms.
If there are symptoms thought to be related to the Chiari, or if there is a syrinx present, treatment is often recommended. There are two surgical options for management of a Chiari malformation.
Extradural decompression
An incision is made in the back of the head/upper neck. The muscles in the back of the neck are then separated to expose the skull and the back of the upper cervical vertebrae. A portion of this bone is removed to decrease pressure around the Chiari. Finally, the layers of muscle and skin are closed using sutures.
Intradural decompression
The procedure begins with extradural decompression, as described above. Following this, the covering of the brain and spinal cord, known as the dura, is opened. Often, the surgeon will use cautery to reduce the cerebellar tonsils. A graft material is then sewn in to close the dura, expanding the area around the Chiari for decompression. Finally, the layers of muscle and skin are closed with sutures. Since the dura is opened during the procedure, a drain is typically inserted and left in place for several days after the surgery, before being removed at the bedside.
Risks
Generally, a Chiari decompression is considered a safe procedure, but like any surgery, there are some risks, though they are usually low. These risks include infection, which is why your child will receive antibiotics before the surgery. Other risks include bleeding, ongoing Chiari symptoms even after the surgery, and the possibility of needing another operation.
With an intradural decompression, where the covering of the brain containing the cerebrospinal fluid (CSF) is opened, there's an added risk of a CSF leak. This might need medication or a longer time for the drain to be in place. Sometimes, a re-operation might be necessary to fix this issue. Additionally, patients who undergo intradural decompression are at risk of developing chemical meningitis, which is not a true infection, but an irritation to the body from surgery itself. It usually lasts a few days to weeks and can cause symptoms like headache, neck pain, light sensitivity, and fever. It is often treated with steroids. Occasionally, a patient may develop a pseudomeningocele, which is a pocket of spinal fluid that collects under the incision. Usually, this resolves on its own over time as the body absorbs the fluid. However, if it persists or if there's leakage from the incision, another surgery might be needed, and rarely, a shunt may be needed.
Follow up
After discharge from the hospital, your child may return to school or work when they feel ready. They should not participate in gym, contact sports or swimming until cleared by neurosurgery at the post-operative visit, which is typically 4-6 weeks after surgery. Your child's neurosurgeon will decide when follow-up imaging is needed, but usually, the first MRI after surgery is scheduled for about 6 months later.
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Reviewed July 2024 by Allison Rodman PA-C