As of 2001, doctors had not yet found the generesponsible for Arnold-Chiari malformations. There has not yet been a study that shows whether or not this disorder is inherited, but there are reports of several families where more than one family member has a Arnold-Chiari malformation.
Scientists do not know what causes Arnold-Chiari malformations. One hypothesis is that the base of the skull is too small, forcing the cerebellum downward. Another theory focuses on overgrowth in the cerebellar region. The overgrowth pushes the cerebellum downward into the spinal canal.
Arnold-Chiari malformations are rare. As of 2001, there is no data that shows the incidence of Arnold-Chiari malformations. Arnold-Chiari malformations are the most common type of malformation of the cervicomedullary junction, the area where the brain and spine connect. About one percent of live newborns have a malformation in the cervico-medullary junction.
Signs and symptoms
Some people with Arnold-Chiari I malformations have no symptoms. Typically, with an Arnold-Chiari I malformation symptoms appear as the person reaches the third or fourth decade of life. Symptoms of this disorder vary. Most symptoms arise from the pressure on the cranial nerves or brain stem. The symptoms may be vague or they may resemble symptoms of other medical problems, so diagnosis may be delayed.
One of the most common symptoms of Arnold-Chiari malformations is a headache. The headache generally begins in the neck or base of the skull and may radiate through the back of the head. Coughing, sneezing, or bending forward may bring on these headaches. The headaches can last minutes or hours and may be linked with nausea.
There may be pain in the neck or upper arm with Arnold-Chiari malformations. Patients often report more pain on one side, rather than equal pain on both sides. There may also be weakness in the arm or hand. Patients may also report tingling, burning, numbness, or pins and needles. Balance can be affected as well. A person may be unsteady on their feet or lean to one side.
Some people with Arnold-Chiari malformation may have difficulty swallowing. They may say that food 'catches' in their throat when they swallow. Another common complaint linked with Arnold-Chiari malformations is hoarseness.
People with Arnold-Chiari malformations may have visual problems, including blurred vision, double vision, or blind spots. There may be bobbing of the eyes.
Lisa A. Fratt, The Gale Group Inc., Gale, Detroit,