Are there different types of Chiari malformation?

Are there different types of Chiari malformation?

There are several types of Chiari malformations that are distinct entities from each other but share some similarities. Doctors categorize the disorder based on anatomical findings and associated conditions. The main types are:

• Chiari malformation type I: People with type I may not have any symptoms or they may not develop symptoms until they are adolescents or adults. Type I occurs when the lower part of the cerebellum extends into the hole (the foramen magnum) at the base of the skull. The spinal cord normally passes through this hole. Type I is the most common form of Chiari malformation.
• Chiari malformation type II: Type II is part of a complex malformation that occurs during brain and spine development in utero. Type II is most commonly found in patients with the most severe form of spina bifida called myelomeningocele. Myelomeningocele occurs when the backbone and spinal canal don’t close properly before the baby is born. Surgery is required to close the spine after birth, and paralysis can occur below the area where the spine is malformed. With type II malformation, there is often both cerebellum and brain stem herniation into the spinal canal, along with other additional brain abnormalities. People with type II may require surgery to treat the other associated conditions, but only require treatment of the Chiari type II if they have symptoms.
• Chiari malformation type III: This is a rare and most severe of the Chiari malformations. It occurs when some of the cerebellum and brain stem extend through an abnormal opening in the back of the skull (not the foramen magnum). In addition, some of the membranes that surround the brain or spinal cord extend through the opening. This malformation results in a swelling at the back of the skull called an encephalocele. Type III causes severe, life-threatening symptoms and they appear early in life. Children with type III have neurological problems, learning delays and seizures. These often require surgery.

Some scientists classify two other types -- type IV and type 0. Type IV is a rare type and happens when the cerebellum itself is underdeveloped or has parts missing. Parts of the skull and spinal cord may be visible. This type is severe and usually fatal in infants.

Type 0 is a very rare entity. In this type, there is little or no extension of parts of the cerebellum into the foramen magnum but there is significant crowding at that level. Symptoms are thought to be caused by abnormal flow of cerebrospinal fluid at the base of the skull.