What is a Chiari I malformation?
Chiari (pronounced key-AR-ee) malformation is a condition in which the lower part of the brain, called the cerebellar tonsil, herniates down through the skull and into the spinal canal. There are several different types of Chiari:
- Chiari type I, the most common, affects both children and adults. Because the back of the skull is too small or deformed, a crowding of the brainstem, cerebellum, and tonsils occurs. As the tonsils push out the skull, they block cerebrospinal fluid (CSF) flow. Chiari I may cause a fluid-filled cyst (syrinx) in the spinal cord.
- Chiari type 0, a newly identified form of Chiari, describes the absence (or a “zero” herniation) of the tonsils below the foramen magnum. Yet Chiari 0 includes the presence of both symptoms and a syrinx in the spinal cord. This new type is under study and controversial.
- Chiari type II is present at birth and affects infants. It occurs with the birth defect myelomeningocele, a form of spina bifida. When the spinal canal does not close before birth, some of the spinal cord protrudes like a sac from the baby’s back. Both the brainstem and tonsils are pulled down into the spinal canal to block CSF flow in the brain and causing hydrocephalus. This type is correctly called Arnold-Chiari malformation.
- Chiari type III affects infants and is a rare but severe herniation that involves the cerebellum. It can develop with the birth defect encephalocele, a fluid-filled sac at the back of the baby’s neck.
- Chiari type IV affects infants. This rare and often fatal malformation occurs when the cerebellum does not develop properly.
What causes a Chiari I malformation?
Chiari begins with the underdevelopment of the fetal skull during pregnancy. During childhood, the brain continues to grow and the skull hardens. However, the small size or shape of the Chiari skull is mismatched to the size of the brain. Thus, a crowding of the brainstem, cerebellum, and tonsils occurs. Crowing pushes the tonsils out of the skull through the opening (foramen magnum) where the spinal cord exists. Herniation of the cerebellar tonsils can extend several millimeters below the foramen magnum. The tonsils put pressure on the brainstem and spinal cord, block CSF flow, and result in Chiari signs and symptoms.
What are symptoms of a Chiari I malformation?
Chiari I symptoms vary from patient to patient and are not necessarily related to the size of tonsillar herniation. Some people with large herniations have no symptoms (asymptomatic). Yet others with small herniations have severe symptoms. When symptoms are present, they are often vague or nonspecific. As a result, the diagnosis of Chiari is often delayed until more severe symptoms occur or after symptoms persis for some time. Symptoms are caused by disruption of the CSF flow and compression of nervous tissues.
Because the brainstem is responsible for most body functions, Chiari causes all kinds of strange symptoms. People may experience symptoms that range from headache to irritable bowel. The five most common symptoms are:
- Pressure like headaches at the back of the skull that worsen with physical strain or coughing; often with neck pain
- Hoarseness or swallowing problems
- Sleep apnea
- Weakness or numbness in an extremity
- Balance problems
People with Chiari I often develop symptoms during their teen or early adult years. This disorder is also seen in young children and older adults. In some cases, a head or neck injury from a car accident or sports injury triggers the onset of symptoms.
How is a Chiari I malformation diagnosed?
The complex symptoms of Chiari I can mimic other diseases – often leading to misdiagnosis and delay in treatment. At times, Chiari I is mistaken for fibromyalgia, chronic fatigue syndrome, migraine, multiple sclerosis, mental disorder, depression, sinus disease, trigeminal neuralgia, or other neurological disorders.
There is no specific test to confirm Chiari. Rather, a diagnosis is made by assessment of the patient’s symptoms, neurological exam, and MRI findings.
A complete medical history and physical exam can determine if your symptoms are related to Chiari or another problem. A neurological exam detects problems with cranial nerves such as gag reflex, facial numbness, hoarseness, double vision, tremors, and vision problems. You may be asked ot see an eye or ear specialist, or to undergo a sleep evaluation. Your doctor will order one or more imaging studies including:
- MRI scan
- X-rays
- CT scan
- Cine MRI scan – special study used to observe CSF flow. This test can determine if, and by how much, a Chirai is blocking the back-and-forth flow of CSF between the brain and spine.
What are treatment options for a Chiari I malformation??
Treatment options vary depending on the severity of symptoms, the extent of tonsil herniation, and the presence of other conditions such as syringomyelia. Regular check-ups and periodic MRI scans for those with mild or no symptoms. Headache can be relieved with anti-inflammatory or pain-relieving drugs.
Surgery may be advised for those with moderate to severe symptoms or with a syrinx. The goals of surgery are to stop or control the progression of symptoms caused by herniation of the cerebellar tonsils and relieve compression of the brainstem. Types of surgery include:
- Posterior fossa decompression – surgery removes bone (craniectomy) at the back of the skull and spine to widen the foramen magnum. The surgeon opens the dura overlying the tonsils and sews a dura patch to expand the space, similar to letting out the waistband on a pair of pants. After surgery, symptoms related to the blockage of CSF should decrease as flow normalizes.
- Spinal fusion – may be performed in addition to decompression surgery in certain patients with spine instability. The neck area of the spine may be unstable due to scoliosis, Ehler-Danlos syndrome, or other bone abnormality. Rods and screws are inserted to reinforce the skull and neck vertebrae.
- Shunting – is used to reroute CSF. The shunt includes a flexible tube with a 1-way valve that directs the fluid out in the desired direction. For a syrinx in the spinal cord, one end of the tubing is placed in the syrinx. The other end is placed outside the spinal cord. For hydrocephalus, one end of the tubing is placed in the ventricle of the brain. The other end is placed in the abdomen (called a ventriculoperitoneal shunt). A shunt remains inside the body after surgery. However, shunts pose risks and often become clogged or dislodge. Repeated surgeries may be necessary.
- Transoral decompression – is a surgical procedure to treat basilar invagination. The surgery is performed through the mouth and to the back of the throat to remove an abnormal odontoid bone (C2 vertebra).
Are there clinical trials for a Chiari I malformation?
Clinical trials are research studies in which new treatments — drugs, diagnostics, procedures, and other therapies — are tested in people to see if they are safe and effective. Research is always being conducted to improve the standard of medical care. Information about current clinical trials, including eligibility, protocol, and locations, are found on the Web. Studies can be sponsored by the National Institutes of Health (see www.clinicaltrials.gov) as well as private industry and pharmaceutical companies (see www.centerwatch.com).
If you have more questions or would like to schedule an appointment with one of our Spine Center specialists, please call 515.875.9560.