When the portion of the skull containing the cerebellum is deformed or too small, pressure is exerted on the brain and, in some circumstances, on the brain stem as it enters the spinal canal. This condition, known as a chiari malformation, and the resulting pressure can lead to a host of neurological problems; because the normal flow of cerebrospinal fluid is interrupted, the normal transmission of signals between the brain and the body is compromised.

Chiari malformations are most likely the result of problems in the pre-natal (fetal development) stage, and may also have a genetic or hereditary component. When they are diagnosed they are classified into four different categories: in adults (Type I, the most common type) they’ve developed during brain and skull growth and the symptoms aren’t seen until later in life; in Type II the malformation is congenital and puts pressure on both the cerebellum and the brain stem in the upper spinal canal. Infants suffering with spina bifida and complete or partial paralysis or those with hydrocephalus (too much cerebral spinal fluid in the brain) are most likely to suffer from this type; with Type III, both the cerebellum and brain stem are being forced into the spinal canal opening, causing the rear of the brain to protrude from the back of the skull and resulting in severe neurological problems and issues; and Type IV of the malformation arises when the cerebellum develops abnormally, having missing portions or developing much further down into the spinal canal.

Type I chiari malformations present with headaches, neck pain radiating down the shoulders and problems with walking and coordination. There may also be a change in sensation in the feet and hands and problems with speech, vision, and motor skills as well as chest pains and abnormal spinal curves. Type II, III and IV sufferers will have symptoms consistent with spinal bifida and other congenital birth defects that will be obvious in the post-natal stage. These are typically definitively diagnosed with a physical exam and image testing.

If symptoms are mild and not affecting quality of life, a physician will likely recommend monitoring and pain- and inflammation-relieving medications. However surgery will be required in cases of severe malformation in order to alleviate any impact on the brain and spinal canal if and when the condition worsens. Surgeries aim to relieve pressure on the brain stem and spinal cord and canal, and may include a spinal laminectomy or a posterior fossa craniectomy.