Chiari malformations are structural defects that affect tissue in the brainstem, cerebellar (the area of the brain at the back of the skull), and spinal cord. They can cause symptoms ranging from headaches and muscle weakness to developmental delays and breathing problems. Typically, they occur in the area where the brain and spinal cord meet. In most cases, parts of the brain push down into the spinal canal and cause pressure in the brain and on the spinal cord. This often blocks the flow of cerebrospinal fluid (CSF), which can cause fluid-filled cysts on the spinal cord (called syringes) and hydrocephalus (a buildup of fluid in the brain). There are four types of Chiari malformations. Types I and II are more common, while types III and IV are rare.
Type I is the most common and can go undiagnosed until symptoms develop during childhood, adolescence, or even into adulthood. This type can cause syringomyelia (when syringes form on the spinal cord). This can cause paralysis, weakness, and stiffness in the back and limbs. Scoliosis (spine curvature) is often associated with this type.
Type II typically affects children born with spina bifida, specifically infants with myelomeningoceles -- spinal cord tissue that protrudes through an opening in the spine.
Type III is a rare and very serious form of Chiari malformation. Some parts of the brain may stick out, or herniate, through an abnormal opening in the back of the skull.
Type IV is very rare. In this type, part of the brain is underdeveloped or missing.