A Chiari I malformation occurs when the back of the skull is just a little too cramped and the cerebellum is "squished" down into the foramen magnum, which is the opening of the spinal column. There are many theories as to why and how Chiari I malformation occurs, but a common explanation is that it occurs before we are even born. It is often called a congenital malformation, because most people are born with this abnormal skull anatomy.
Revised: 2/2020