Chiari Malformation Health Article

Demographics

The true incidence of Chiari malformation is unknown. Some researchers believe that there may be far more cases of Type I malformation, in particular, than reported since many individuals with Type I malformation experience few if any symptoms. Most researchers agree that the rate of both Type I and Type II Chiari malformation is approximately 1 percent of all live births. Of those with Type I malformation, approximately 25 percent also have syringomyelia. However, the majority of all Chiari malformations are Type II and are almost exclusively associated with spina bifida defects. Spina bifida occurs in approximately one to two per 1,000 births. As access to imaging testing such as MRI has increased, so has the number of children diagnosed with Chiari malformation Type I. Therefore, the incidence of known Type I Chiari malformation is anticipated to increase.

Causes and symptoms

All Chiari malformations are present at birth, though symptoms may not begin until years later. The exact cause is unknown; however, it is suspected that, at some point during embryonic development, an increased pressure in the brain may cause brain structures to be displaced or moved into the spinal canal. Other possible causes for this malformation include exposure to harmful substances during fetal development or genetic factors. In general, there are several accepted theories of what may lead to problems that affect normal development of the brain: exposure to toxic or harmful substances; a lack of proper vitamins and nutrients in the mother's diet during pregnancy; infection; maternal use of prescription medication, illegal drugs, or alcohol; and genetic or familial factors. Chiari malformations are found in several known genetic disorders such as achondroplasia, Hadju-Cheney syndrome, and Klippel-Feil syndrome. Similarly, studies of families and identical twins with Chiari malformation show that the malformation occurs more often in these families than in families in which no member is affected. Another proposed cause for Chiari malformation is an abnormality in bone development. Chiari malformation may result because the cerebellum is of normal size, but the bones at the base of the skull are too small.

Symptoms of Chiari malformation vary according to the type of malformation. In Type I Chiari malformation, symptoms may begin anytime between infancy and early adulthood. Depending on when it is diagnosed, these symptoms may include blurred or double vision; involuntary eye movements; headache, usually at the base of the skull or upper neck which may become worse with coughing or straining; scoliosis or an abnormal curvature of the spine; dizziness and impaired muscle coordination; low muscle tone; alteration of the voice or a high-pitched cry; frequent respiratory tract infections, vomiting and difficulty swallowing; drop attacks (a sudden loss of muscle control that results in a collapse to the floor); and central cord syndrome, a pattern of reduced sensation and weakness in the arms.

Symptoms of Type II Chiari malformation include those that occur in Type I malformation. Victims may also exhibit vocal cord paralysis and episodes of apnea (a cessation of breathing sometimes requiring resuscitation). Type II malformation occurs almost exclusively with spina bifida, which causes symptoms that may include paralysis of the lower extremities (and less often, the upper limbs), and bowel and bladder dysfunction. If the child has hydrocephalus, these symptoms may worsen and can be fatal unless the hydrocephalus is treated.