Chiari malformations (types I-IV) are a group of congenital brain abnormalities affecting the structural relationships between the cerebellum, brainstem, the upper cervical cord, and the bony cranial base. Chiari type I malformation is the most common and the least severe of the spectrum and is often diagnosed in adulthood. The prevalence of Chiari I is 0.1-0.5% with a slight female predominance. Most patients with CMs have no symptoms and their malformations are discovered while conducting diagnostic procedures for other disorders. Symptoms include headaches, neck pain, dizziness and balance problems, muscle weakness, numbness or tingling in the arms or legs, blurred vision, double vision, sensitivity to light, insomnia and depression.
The hallmark of Chiari I malformation is a cerebellar tonsillar herniation below foramen magnum. Some CM1 patients are asymptomatic and the condition does not interfere with a person’s activities of daily living. In other cases, medications may ease certain symptoms, such as pain.
Chiari malformations type I follows an autosomal dominant inheritance pattern. The molecular basis of the disease is unknown.