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Chiari malformations are structural defects in the cerebellum. That's thepart of thebrainthat controls balance.

Some people with Chiari malformations may have no symptoms. Othersmay have symptoms such as:

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dizziness muscle weakness numbness vision problems headaches problems with balance and coordinationChiari malformations affect females more often than males.

Scientists once believed that Chiari malformations occurred in only 1 in

every 1,000 births. But the increased use of diagnostic imagingtechniques such as CT scans and MRIs suggests that the conditionmay be much more common.

Accurate estimates are difficult to make. That's because some childrenwho are born with the condition either never develop symptoms or don'tdevelop symptoms until they reach adolescence or adulthood.

Causes of Chiari Malformations

Chiari malformations are usually caused by structural defects in thebrain and spinal cord. These defects develop duringfetal development.

Due to genetic mutations or a maternal diet that lacked certain nutrients,the indented bony space at the base of the skull is abnormally small. Asa result, pressure is placed on the cerebellum. This blocks the flow ofthe cerebrospinal fluid. That's the fluid that surrounds and protects thebrain and spinal cord.

Most Chiari malformations occur during fetal development. Much lesscommonly, Chiari malformations can occur later in life. This can happenwhen an excessive amount of cerebrospinal fluid is drained away

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because of:

injury infection exposure to toxic substances

Types of Chiari Malformations

There are four types of Chiari malformations:

Type I. This is by far the most commonly observed type in children. Inthis type, the lower part of the cerebellum -- but not the brain stem --extends into an opening at the base of the skull. The opening is calledthe foramen magnum. Normally, only the spinal cord passes throughthis opening.

Type I is the only type of Chiari malformation that can be acquired.

Type II. This is usually only seen in children born withspina bifida.Spina bifida is the incomplete development of the spinal cord and/or itsprotective covering.

Type II is also known as "classic" Chiari malformation or Arnold-Chiarimalformation. In type II Chiari malformation, both the cerebellum andthe brain stem extend into the foramen magnum.

Type III. This is the most serious form of Chiari malformation. It involves

the protrusion or herniation of the cerebellum and brain stem throughthe foramen magnum and into the spinal cord. This usually causessevere neurological defects. Type III is a rare type.

Type IV. This involves an incomplete or undeveloped cerebellum. Itsometimes is associated with exposed parts of the skull and spinal cord.Type IV is a rare type.

In addition to spina bifida, other conditions sometimes associated withChiari malformations include:

Hydrocephalus.An excessive buildup of cerebrospinal fluid in thebrain.

Syringomyelia.A disorder in which a cyst develops in the spinal cord'scentral canal.

Tethered cord syndrome.A progressive disorder in which the spinalcord attaches itself to the bony spine.

Spinal curvature. This includes conditions such as:

scoliosis(a bending of the spine to the left or right)kyphosis(a forward bending of the spine)

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Symptoms of Chiari Malformations

Chiari malformation is associated with a wide range of symptoms whichvary by type.

Type I Chiari malformation usually causes no symptoms. Most peoplewith the condition don't even know that they have it unless it isincidentally discovered during a diagnostic imaging test.

But if the malformation is severe, type I may cause symptoms such as:

Pain in the lower back of the head into the neck.It usually developsquickly and intensifies with any activity that increases pressure inthe brain, such ascoughingand sneezing.

Dizzinessand problems with balance and coordination.

Swallowing difficulties. Sleep apnea.Most children born with type II Chiari malformation have hydrocephalus.Older children with type II Chiari malformation may develop head painassociated with:

coughing or sneezing bending over strenuous physical activities straining to have a bowel movement

Some of the most common symptoms are linked to problems with thefunction of nerves in the brain stem. These include:

weakness of vocal cords swallowing difficulties breathing irregularities serious changes in the function of nerves in the throat andtongueTreatment of Chiari Malformations

If a Chiari malformation is suspected, a doctor will perform a physical

exam. The doctor will also check functions controlled by the cerebellumand spinal cord. These functions include:

balance touch reflexes sensation motor skillsThe doctor may order diagnostic tests, such as:

X-ray

CT scan MRI

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An MRI is the test most often used to diagnose Chiari malformations.

If Chiari malformations cause no symptoms and do not interfere withactivities of daily living, no treatment is necessary. In other cases,medications can be used to manage symptoms such as pain.

Surgery is the only treatment that can correct functional defects or stopprogression of damage to the central nervous system.

In both type I and type II Chiari malformations, the goals of surgery areto:

Relieve pressure on the brain and spinal cord. Re-establish normal fluid circulation through and around the area.In adults and children with Chiari malformations, several types ofsurgery can be performed. These include:

Posterior fossa decompression surgery. This involves the removal ofa small portion of the bottom of the skull and sometimes part of thespinal column to correct the irregular bony structure. The surgeon alsomay open and widen the dura. That's the firm covering of the brain andspinal cord tissues. This creates additional space for the cerebrospinalfluid to circulate.

Electrocautery. This uses high-frequency electrical currents to shrinkthe lower part of the cerebellum.

Spinallaminectomy.This is the removal of part of the arched, bonyroof of the spinal canal. This increases the canal's size and reducespressure on the spinal cord and nerve roots.

Additional surgical procedures may be needed to correct conditionsassociated with Chiari malformations such as hydrocephalus.

Surgery usually results in a significant reduction of symptoms and aprolonged period of remission. According to Children's Hospital inBoston, which specializes in the treatment of Chiari malformations,

surgery virtually eliminates symptoms in 50% of pediatric cases.Surgery substantially reduces symptoms in another 45% of cases.Symptoms are stabilized in the remaining 5%.

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