Overview

Chiari malformation describes a condition in which a portion of the brain herniates, pushing through the opening at the base of the skull. As the herniated tissue pushes through this opening, it presses against the brainstem, blocking the flow of cerebrospinal fluid (CSF). Chiari malformations may be present at birth (congenital). In some patients, the symptoms may not appear until adulthood. Depending on the extent of herniation, these malformations cause a complex of symptoms that vary from mild to severe.

Of the several types of Chiari malformations, Chiari I is the most common. Although it is the mildest form, symptoms can progress, causing severe pain and debilitating deficits. Chiari I malformation may remain undiagnosed until adulthood because symptoms are either absent, delayed, or misdiagnosed. Chiari II and III malformations affect infants; these more severe brain herniations require more prompt treatment.

The ventricles and CSF system

To understand how a Chiari I malformation causes symptoms it is helpful to know how the ventricular system works (Fig. 1). Cerebrospinal fluid (CSF) is a clear, watery substance that flows within and around the brain and spinal cord to help cushion it from injury. This circulating fluid is constantly being absorbed and replenished. CSF is produced by the choroid plexus inside hollow channels in the brain called ventricles. The CSF flows through the ventricles and out into the subarachnoid space where it is reabsorbed into the venous sinus. The brain normally maintains a fine balance between the amount of CSF that is absorbed and the amount that is produced. A disruption or blockage in the system can cause a build up of CSF, which can cause enlargement of the ventricles (known as hydrocephalus) or cause a collection of fluid in the spinal cord (known as syringomyelia).

What is a Chiari I malformation?

When the bony skull base (called the posterior cranial fossa) is too small or misshapen, it compresses a portion of brain (cerebellum). The brain is then pushed down and squeezed out (herniation) of the nearest opening (Fig. 2). This bony opening is the foramen magnum. Herniation of the cerebellar tonsils can extend several millimeters (greater than 5mm) below the foramen magnum. The herniation then puts pressure on the brainstem and spinal cord, and blocks CSF preventing its flow over the brain.

As the extent of herniation varies among patients, so do the symptoms vary in severity and type. The malformation caused by this bony defect progressively affects the brainstem and spinal cord. The flow of CSF is blocked, leading to a variety of neuromuscular deficits.

Syringomyelia, hydrocephalus, and other complications. In some cases, the CSF accumulates within the spinal canal where it eventually forms a syrinx or cyst. This condition, called syringomyelia, causes more neurological problems by damaging the spinal cord. Syringomyelia affects about 65% of patients with Chiari I malformation [1]. In some case, the CSF accumulates 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 and cranial cervical instability.

What are the symptoms?

The symptoms of Chiari I malformation relate to the extent and the area affected by the herniation. Some patients with Chiari I malformation have no symptoms. Other patients are typically affected by pressure-like headaches or pain at the base of the skull or neck. Typical to a headache caused by Chiari I, these symptoms can worsen with physical strain, coughing, or change in position.

Symptoms are caused by disruption of the CSF flow and compression of nervous tissues. Some patients experience sensory deficits such as vision problems (e.g., floaters, flashing lights), dizziness, and swallowing difficulties. Motor deficits can include weakness or tingling in the hands or feet, gait problems, difficulties with balance and coordination, or pseudotumor-like symptoms. Symptoms of pain or sensation problems may flare up. Other symptoms may include ringing or buzzing in the ear, sleep apnea, and snoring.

Table 1. Common symptoms of chiari I and syringomyelia.

Chiari I

Syringomyelia

Severe head and neck pain
Headaches brought on by coughing, sneezing or straining
Difficulty swallowing
Frequent gagging and choking
Dizziness and vertigo
Balance problems
Muscle weakness
Loss of fine motor skills
Poor hand coordination
Blurred or double vision
Hypersensitivity to bright lights
Nystagmus (involuntary eye movements)
Difficulty in tracking objects
Tinnitus (buzzing or ringing in the ear)
Hearing loss
Vocal cord paralysis
Sleep apnea

Headaches and chronic pain
Loss of sensitivity, especially to hot and cold
Muscle weakness and spasticity
Numbness in hands and feet
Motor impairment
Loss of bowel and bladder control
Osteoporosis and scoliosis
Paralysis or quadriplegia

Patients with Chiari I malformations often develop symptoms during their teen or early adult years. Less often, the disorder is seen in young children and older adults. In some cases, trauma triggers the onset of symptoms.

The symptoms are complex, progressing over time. Because of this complexity, the condition is often misdiagnosed. At times, Chiari I malformation is mistaken for fibromyalgia, migraine headaches, sinus disease, multiple sclerosis, and other complex disorders of the nervous system. Some patients have waited for years before an accurate diagnosis is made. Accurate diagnosis and plan of treatment is important before the patient’s nervous system suffers permanent injury.

What are the causes?

Recent studies suggest that this malformation occurs during embryonic development. It may be caused by underdevelopment of the bony skull base (posterior cranial fossa). The bony skull may be too small for the normally developed brain, specifically the cerebellum.

Who is affected?

Chiari I malformation has been seen on imaging studies in patients of all ages. However, patients typically seek medical attention in their 20s and 30s. Three times more women than men are affected [1]. Some genetic studies show that this condition runs in some families [1]. As each patient may be affected differently, the best medical and surgical management will vary.

How is a diagnosis made?

The symptoms of Chiari I malformation can mimic other diseases. It affects sensory and motor functions. A complete medical history and physical examination can identify if the symptoms are related to Chiari I or another problem. A neurological examination can detect problems with cranial nerves such as gag reflex, facial numbness, hoarseness, double vision, tremors, and disturbances of vision. You may be asked to see an eye (ophthalmologist) or ear (otolaryngologist) specialist to complete your evaluation. Your physician will perform a complete neurologic exam to confirm that the Chiari I malformation is the cause of your symptoms.

Your doctor will order one or more imaging studies to confirm the diagnosis. These include:

Magnetic resonance imaging (MRI) scan is a noninvasive test used to evaluate the patient’s brain, spinal cord, and surrounding CSF. MRI studies will identify the extent of cerebellar herniation, from several millimeters to centimeters (Fig. 3). The herniation may reach to the level of the first two vertebra of the cervical spine (C1 or C2). As a result of the herniation, other anatomical abnormalities may be seen at C1 and C2. In some patients, MRI can also detect an abnormal accumulation of CSF within the spinal canal (Fig. 4). This fluid-filled cavity (syrinx) is surrounded by stretched tissues of the spinal cord.

Cine MRI is a special type of study performed to observe and detect obstruction of CSF flow (Fig. 5).

Computed tomography (CT) scan is used to view the bony skull base and spinal column.

What treatments are available?

Treatment options vary depending on the severity of symptoms, the extent of tonsilar herniation, and the presence of associated conditions such as hydrocephalus, syringomyelia, and disorders of the skull and spine.

Observation
If you have mild or no symptoms, monitoring by regular exam may be recommended. If you have symptoms of pain, pain medication (e.g., anti-inflammatory) may provide relief. Take measures to minimize neck strain in daily activities and while sleeping; use a good pillow. Avoid chiropractic manipulation as it can make the herniation worse or aggravate the brain injury.

Surgery
In patients whose pain are severe or a syrinx is present, surgical treatment is advisable. In general, the goals of surgery are to relieve the progression of symptoms caused by the herniation of the cerebellar tonsils, and compression of the brain stem and cranial nerves. In patients with a syrinx, the goal is prevention or control of progression. Symptoms related to the obstruction of CSF should decrease as flow normalizes.

Posterior fossa decompression is a surgical procedure that removes bone at the back of the skull and spine to widen the foramen magnum. The dura overlying the tonsils is opened and a dural patch is sewn to expand the space and restore normal CSF flow.
Shunt. In some cases a shunt is inserted into the syrinx cavity to reroute the cerebrospinal fluid from the spinal cord.

What happens during surgery?

The most common procedure performed is a posterior fossa decompression. The operation will take about 2 to 3 hours.

Step 1. Patient preparation
After admission to the hospital, you are readied for surgery. In the operating room, an intravenous (IV) line is placed in your arm and general anesthesia is administered to put you asleep. While you lie face down on the operating table, your head is fixed in place by skull fixation. This device, which attaches to the table, holds your head in position during the procedure.

Step 2. Skin incision
The area is prepped with an antiseptic. A skin incision is made through the neck muscles so that the surgeon can see the skull and top of the spine. The skin incision is about 3-4 inches long (Fig. 6).

Step 3. Bone removal
The skin and muscles are lifted off the bone and folded back. The surgeon removes a small section of skull at the back of your head, called a craniectomy. The bone flap is lifted and removed. Sometimes the bony arch of the C1 vertebra is removed, called a laminectomy. These steps expose the protective covering of the brain and spinal cord called the dura (Fig. 7). The CSF flows in between the dura and the brain and spinal cord. Bone removal effectively decompresses the area and relieves the crowding in the posterior fossa to restore normal flow of CSF.

Step 4. Dura opening
Most patients undergo an additional step of opening the dura with scissors. However, not all patients require this step because bone removal alone may restore normal CSF flow. Some surgeons perform a Doppler ultrasound study during surgery to determine if opening the dura is necessary.

Step 5. Dural patch (duraplasty)
A patch of the patient’s tissue is sutured into place to enlarge the dura opening (Fig. 8). This effectively enlarges the space around the herniated tonsils.

Step 6. Closure
The dural patch is sutured in a watertight fashion and the suture line is covered with a dural sealant to prevent CSF leak. The small area where bone has been removed is covered by the strong neck muscles and skin, which are sutured together. A soft adhesive dressing is placed over the incision.

What happens after surgery?

After decompression, you will awake in the recovery room and be monitored for overnight. You will remain in the hospital for 2 to 3 days. After surgery, typical symptoms may include headache and neck pain that may last for several days.

Possible risks of surgery include:

2-5% risk of pseudomeningocele or CSF leak
1% risk of infection
Risk of head and neck pain is variable
Neurological deficit is rare

What are the results of treatment?

The results of your decompression surgery depend on the severity of the Chiari malformation and the extent of any previous brain and nerve injury before treatment. Eighty five to 95% of patients experience some relief of their symptoms [2]. However, nearly 50% of patients may continue to have residual effects from syringomyelia, particularly if the injury to the spinal cord has been advanced.

Follow up is needed to continue to monitor CSF flow and the syrinx site. For any residual symptoms (e.g., neck pain) or headache, you and your doctor will discuss possible options to determine the best care.

Clinical trials

Clinical trials are research studies in which new treatments—drugs, diagnostics, procedures, and other therapies—are tested in people to assess their safety and efficacy. Research is always being conducted to improve the standard of medical care. Information about current clinical investigations, including their eligibility, protocol, and participating locations are found on the web. Clinical trials are sponsored by the National Institutes of Health (NIH), www.clinicaltrials.gov, as well as by private industry and pharmaceutical companies, www.centerwatch.com

Current Studies
Click here for information about clinical trials conducted by our doctors at local Cincinnati hospitals or call 1-800-325-7787 ext. 5260.

Sources & Links

If you have more questions, please contact the Mayfield Clinic at 800-325-7787 or 513-221-1100. Additional information is available on the web.

Links
World Arnold Chiari Malformation Association www.wacma.com
American Syringomyelia Alliance Project www.asap.org
www.conquerchiari.org

Sources

Milhorat TH, Chou MW, Trinidad EM, Kula RW, Mandell M, Wolpert C, Speer MC. Chiari I malformation redefined: clinical and radiographic findings for 364 symptomatic patients. Neurosurgery 44(5):1005-17, 1995
Bindal AK, Dunsker SB, Tew JM Jr. Chiari I malformation: classification and management. Neurosurgery 37(6):1069-74, 1995

Glossary

cerebrospinal fluid (CSF): a clear fluid produced by the choroid plexus in the ventricles of the brain. CSF bathes the brain and spinal cord, giving them support and buoyancy to protect from injury.

craniectomy: surgical removal of a portion of the skull.

dura mater: the outer protective covering of the brain.

hydrocephalus: an abnormal build-up of cerebrospinal fluid usually caused by a blockage of the ventricular system of the brain. Increased intracranial pressure can compress and damage brain tissue.

pseudomeningocele: an abnormal collection of cerebrospinal fluid (CSF) that communicates with the CSF space around the brain or spinal cord. Unlike a meningocele, the fluid has no surrounding membrane but is contained in a cavity within the soft tissues.

shunt: a drainage tube to move cerebrospinal fluid from inside the ventricles of the brain into another body cavity (e.g., abdomen).

syringomyelia: a chronic progressive disease of the spinal cord caused by an obstruction of normal cerebrospinal fluid (CSF) flow that redirects the fluid into the spinal cord to form a syrinx.

syrinx: a cavity filled with cerebrospinal fluid (CSF) that expands and elongates over time, destroying the center of the spinal cord.

updated: 1.2009
reviewed by: John M. Tew, MD, Nancy McMahon, RN

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Figure 1. Anatomy of the ventricle system and CSF flow through the subarachnoid spaces.

Figure 2. Chiari I malformation.
With the size of the posterior fossa too small, the cerebellar tonsils may herniated through the foramen magnum into the spinal canal, blocking the flow of cerebrospinal fluid.

Figure 3. An MRI of the brain shows the tonsils (arrow) herniating through the foramen magnum (yellow line).

Figure 4. An MRI of the neck shows a collection of cerebrospinal fluid, called a syrinx, has formed in the spinal cord.

Figure 5. A cine MRI movie shows the flow of CSF fluid (white) is blocked by the herniated tonsils in the foramen magnum.

Figure 6. A 3 to 4 inch skin and muscle incision is made down the middle of the neck. Shaded areas represent bone to be removed.

Figure 7. A small portion of the skull is removed (craniectomy). The protective covering of the brain, called the dura, is seen. CSF flows between the dura and brain where it acts as a cushion.

Figure 8. A dural patch is sewn to the dura margins to effectively enlarge the CSF space around the herniated tonsils.