(Definition & Symptoms from Mayo Clinic)
Definition: Chiari malformation is a condition in which brain tissue protrudes into your spinal canal. It occurs when part of your skull is abnormally small or misshapen, pressing on your brain and forcing it downward. Chiari malformation is uncommon, but improved imaging tests have led to more frequent diagnoses.
The adult form, called Chiari malformation type I, develops as the skull and brain are growing. As a result, signs and symptoms may not occur until late childhood or adulthood. The most common pediatric form, called Chiari malformation type II, is present at birth (congenital).
Treatment of Chiari malformation depends on the form, severity and associated symptoms. Regular monitoring, medications and surgery are treatment options. In some cases, no treatment is needed.
Symptoms: Doctors categorize Chiari malformation into four types, depending on the anatomy of the brain tissue that is displaced into the spinal canal, and whether developmental abnormalities of the brain or spine are present.
Many people with Chiari malformation have no signs or symptoms and don't need treatment. Their condition is detected only when tests are performed for unrelated disorders. However, depending on the type and severity, Chiari malformation can cause a number of problems.