What is Chiari Malformation?

Chiari malformation is a rather scary-sounding term that basically means there is not enough room for the brain within the skull, so part of the cerebellum (the lower portion of the brain) is forced downward into the spinal canal. It usually develops as a result of structural defects during fetal development, although depending on the type of CM, symptoms may not occur until adolescence or adulthood.

Types of Chiari Malformation

We generally categorize Chiari malformation into four types:

  • Type I—As the brain and skull are growing, the lower skull and/or spinal cord do not develop properly, pushing the lower part of the cerebellum into the small opening at the base of the skull where the spinal cord comes through. This often does not produce symptoms until late childhood or early adulthood.
  • Type II—This type is evident from infancy, typically as a result of spina bifida, a birth defect in which the spinal cord covering is not properly developed.
  • Type III—The most severe type of CM, this occurs when the cerebellum and brain stem protrude into the spinal column, causing serious neurological symptoms. Fortunately, this is a rare occurrence.
  • Type IV—Another rare type, this CM occurs when the cerebellum itself is underdeveloped.


Because the cerebellum is the part of the brain that controls balance, CM symptoms often include trouble maintaining balance, dizziness or hand coordination difficulties. Other symptoms may include headaches (primarily in the back of the head), numbness in hands or feet, and vision problems. In milder cases of Chiari malformation, there might not be any noticeable symptoms.


In mild cases of CM where few symptoms exist, the doctor may simply recommend monitoring the situation, and in some cases may prescribe pain medication. Where symptoms are more pronounced, surgery is usually the best option. A common surgical procedure to treat CM is posterior fossa decompression, in which the surgeon removes a small portion of the lower skull to give the brain more room and to relieve pressure on the spinal cord. Another possibility is spinal laminectomy, in which the doctor removes a small part of the spinal column to make room.

Chiari malformation is usually diagnosed through a combination of physical exams and imaging tests (most commonly an MRI). For more information about symptoms and treatment options for CM, make an appointment with one of our skilled physicians.