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. An accurate diagnosis and prompt treatment are important to prevent permanent injury to the nervous system.

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 is 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.

Bone deformity

A variety of bone abnormalities can occur in Chiari:

The posterior fossa may be smaller than normal. If too small, the effects can be crowding of the brainstem and cerebellum, as well as herniation of the tonsils through the foramen magnum.
The occipital bone may be misshaped or thickened.
Basilar invagination occurs when the top of the C2 (odontoid) pushes upward into the brain. This defect can narrow the foramen magnum and crowd the brainstem and cerebellum.
Scoliosis is a curvature of the bony spine. There is a high rate of scoliosis with Chiari and syringomyelia, especially in children.
Ehler-Danlos syndrome (EDS) is a connective tissue disorder that may increase the incidence and severity of Chiari. EDS causes joint hypermobility and loose/unstable joints. At the craniocervical junction, strong ligaments attach the C1 and C2 vertebrae to the skull, allowing movement of the head. For someone with both Chiari and EDS, extra testing and precautions are taken to ensure the connection between the spine and skull is intact. Spinal fusion surgery may be needed to support the neck and skull.

Cerebellum herniation

The cerebellum is the lower part of the brain located in the posterior fossa. On the underside of the cerebellum are two tonsils. The cerebellum coordinates body movement. It maintains muscle tone and balance. The cerebellum is also involved in attention, language, memory, and learning. Signs of cerebellum problems include loss of coordination, unstable walking (gait), trouble with speech, and difficulty with eye movement and swallowing.

Brainstem compression

Acting as a relay center, the brainstem connects the cerebrum and cerebellum to the spinal cord. The brainstem performs many automatic functions such as breathing, heart rate, body temperature, wake and sleep cycles, digestion, sneezing, and coughing. Then of the 12 cranial nerves originate in the brainstem.

In Chiari, compression of the brainstem and cranial nerve nuclei can occur. Patients may experience problems with sleeping (pons), breathing (medulla), swallowing, facial pain or numbness, hearing loss, irregular heartbeat, and digestion.

Cerebrospinal fluid blockage

Cerebrospinal fluid (CSF) is a clear, watery-like liquid that flows within and around the brain and spinal cord to help cushion it from injury. This fluid is produced inside the ventricles by the choroid plexus and is constantly being absorbed and replenished.

The CSF flows through the ventricles and out into the space between the brain and skull (subarachnoid space) and down into the spinal canal. A large amount of CSF lies at the back of the cerebellum in an area called the cisterna magna.

As the heart beats, CSF flows into the brain. This is normally balanced by CSF then flowing from the brain into the spinal compartment. In a Chiari malformation, this balanced flow is disrupted. The obstructed CSF begins to force its way like a water hammer through the foramen magnum. Pushing the tonsils down even farther, it exerts pressure on the brainstem. The increasing pressure compromises normal functions of the brain and/or spinal cord and a myriad of symptoms occur.

Excess CSF can collect and enlarge either the ventricles of the brain (hydrocephalus) or form a cyst in the spinal cord (syringomyelia).

Syringomyelia, hydrocephalus, and other complications

When cerebrospinal fluid (CSF) flow is obstructed and collects within the spinal canal, it can eventually form a syrinx. This condition, called syringomyelia (pronounced sir-RING-o-my-elia), damages the spinal cord. The compressed fiber inside the cord cause a wide variety of symptoms. Problems affect the arms or legs, or affect feeling, strength, or balance. Syringomyelia occurs in about 65% of patients with Chiari I malformation.

Is some cases, the CSF collects within the ventricles of the brain (hydrocephalus); this condition may require placement of a shunt to divert this excess fluid. Bony abnormalities, which affect about 25% of patients, can include basilar invagination, scoliosis, and cranial cervical instability.

What are the symptoms?

Chiari I symptoms vary from patient to patient and are not necessasrily 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.

Who is affected?

Chiari I is seen on MRI scans in people of all ages. Its incidence was earlier estimated to affect 1 in every 1,000 births. Now with increasing use of diagnostic imaging, Chiari may be far more common. Patients typically seek medical attention in their 20s and 30s. Three times more women than men are affected. Genetic studies show that Chiari may cluster in some families.

How is a diagnosis made?

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 treatments are available?

Treatment options vary depending on the severity of symptoms, the extent of tonsil herniation, and the presence of other conditions such as syringomyelia. Options could include:

Observation – monitoring by regular check-ups and periodic MRI scan may be recommended for those with mild or no symptoms. Headache can be relieved with anti-inflammatory or pain-relieving drugs.
Surgery – 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.
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).

Clinical trials

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.

Chiari I Malformation