A Chiari malformation is a congenital (present at birth) defect in the area of the back of the head where the brain and spinal cord connect. The condition is also called Arnold Chiari malformation. There are four types of Chiari malformations, including the following:
Type I. Commonly goes unnoticed until problems arise in the adolescent or adult years of life. In this condition, the base of the skull and the upper spinal area are not formed properly.
Type II. This is the most common type of Chiari malformation. In this condition, part of the back of the brain shifts downward through the bottom of the skull area.
Type II Chiari malformations are typically seen in infants who are born with spina bifida, a neurological condition that causes a portion of the spinal cord and the surrounding structures to develop outside, instead of inside, the body.
Type II Chiari malformations can also be associated with a condition known as hydrocephalus. Hydrocephalus is a condition in which there is an overproduction or lack of absorption of the cerebral spinal fluid (CSF) that is found inside of the ventricles (fluid-filled areas) inside of the brain. The increased fluid causes the pressure inside of the head to increase and the skull bones to expand to a larger-than-normal appearance.
Type III. The back of the brain protrudes out of an opening in the back of the skull area.
Type IV. The back of the brain fails to develop normally.
Although the exact cause of Chiari malformation is unknown, it is thought that a problem during fetal development may cause the abnormal brain formation. Chiari malformation may be caused by exposure to harmful substances during fetal development or associated with genetic problems or syndromes that may have a tendency to run in families.
Theories suggest that the following may predispose the fetus to problems that affect the normal development of the head during pregnancy:
The following are the most common symptoms of a Chiari malformation. However, each child may experience symptoms differently. In infants and older children born with this condition, symptoms may include:
The symptoms of Chiari malformation may resemble other conditions or medical problems. Always consult your child's doctor for a diagnosis.
If a Chiari malformation occurs with other congenital (present at birth) defects, the diagnosis may be made at birth. The occurrence of Chiari malformation has thought to be one in every 1,000 births but, with the increased use of diagnostic testing, it may be much more common. Other times, the diagnosis is made after the onset of specific signs and symptoms, and after diagnostic testing. The doctor obtains a complete prenatal and birth history of the child and may also ask if there is a family history of any medical problems. The doctor will also ask about developmental milestones, such as the age the child sat up, crawled, or walked since a Chiari malformation can be associated with other neuromuscular disorders. Developmental delays may require further medical follow-up for underlying problems.
During the examination, a measurement of the circumference of the child's head is taken and compared to a scale that can identify normal and abnormal ranges.
Diagnostic tests that may be performed to confirm the diagnosis of a Chiari malformation include:
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