A Chiari malformation is what occurs when a part of the brain called the cerebellar tonsils gets pushed downward through the foramen magnum, the large hole in the base of the skull through which the spinal cord passes. When the cerebellar tonsils get wedged tightly in this hole, it can cause a certain type of sleep apnea called "central sleep apnea", leading to decreased oxygen reaching the brain, particularly at night. This may hurt brain development. Although most common in children with Pfeiffer syndrome, Chiari malformations may also occur in children with other craniofacial syndromes such as Apert and Crouzon syndrome. You should discuss the need for screening with your craniofacial or pediatric neurosurgeon. Screening may be done with CT scans or MRI's of the brain.