Chiari malformation (CM) is a structural abnormality in the brain in which the cerebellum is located in a lower position than usual. This happens when the skull is abnormally small or misshapen. Under normal circumstances, the cerebellum is situated at the lower rear of the skull, above the foramen magnum (the opening to the spinal canal). When Chiari malformation occurs, the cerebellum is located above the foramen magnum. In this location, more pressure is exerted on the cerebellum and medulla (brain stem), and the functions they control, including balance and motor control, may be adversely affected. This condition may be congenital or develop as the patient grows and it may or may not result in symptoms.
Types of Chiari Malformation
Congenital Chiari malformation, also known as primary Chiari malformation, may be the result of a genetic defect or may be caused by inadequate maternal nutrition during gestation. Acquired, or secondary, Chiari malformation can develop later in life either because of infection, exposure to toxic substances, or as a result of excessive drainage of spinal fluid from the body through injury or as a complication of surgery. The congenital form of this disorder is the more common one.
Chiari malformations are further categorized into several types, the symptoms and severity of which may vary. Type I, the most common variety, is the only type that can be acquired. Patients with Type I may be asymptomatic. It is possible for patients with some types of CM to be free of symptoms in adolescence, but develop symptoms later in life.
Patients with Chiari malformation may also present with a concurrent spinal or brain abnormality, such as:
- Spina bifida
- Tethered cord syndrome
- Spinal curvature