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Chiari (kee-AR-ee) malformation (CM) includes a complex group of disorders characterized by herniation of the cerebellum through the large opening in the base of the skull (foramen magnum) into the spinal canal. The herniated tissue blocks the circulation of cerebrospinal fluid in the brain and can lead to the formation of a cavity (syrinx) within the spinal cord. There are three main types of CM. CM1, the simplest and most prevalent form, is generally considered to be a congenital malformation, although acquired cases are recognized. (See diagrams below.) It is rarely apparent at birth. CM2 and CM3 are more severe congenital malformations that are apparent at birth and associated with complex defects of the brain and spinal cord.
Patients with CM1 may experience no symptoms. When symptoms are present, they usually do not appear until adolescence or early adulthood, but can occasionally be seen in young children. The majority of patients complain of severe headache and neck pain. Other common symptoms are dizziness, vertigo, disequilibrium, visual disturbances, ringing in the ears, difficulty swallowing, palpitations, sleep apnea, muscle weakness, impaired fine motor skills, chronic fatigue and painful tingling of the hands and feet. Because of this complex symptomatology, patients with CM1 are frequently misdiagnosed.
How common is Chiari Malformation?
Until recent years, CM1 was regarded as a rare condition. With the increased availability of magnetic resonance imaging, the number of reported cases has risen sharply. Current estimates range from 200,000 to 2 million Americans with the condition. Genetic studies spearheaded by Dr. Milhorat support a hereditary tendency with a transmissibility rate of 12 percent. Women are affected three times more often than men. Approximately 3,500 Chiari operations are performed each year in the United States.
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