Lindsey has Chiari What?: What is Arnold Chiari Malformation?

Arnold–Chiari malformation, or often simply called Chiari malformation, is a malformation of the brain. It consists of a downward displacement of the cerebellar tonsils through the foramen magnum (the opening at the base of the skull), sometimes causing hydrocephalus, aka "water on the brain", as a result of obstruction of cerebrospinal fluid (CSF) outflow. The cerebrospinal fluid outflow is caused by phase difference in outflow and influx of blood in the vasculature, or the circulatory system, of the brain. The picture below is an MRI showing a herniated cerebellum. AKA Chiari. The size is measured in millimeters. The picture below shows a 4mm herniation. My Chiari when I was first diagnosed at age 14 was 4.5 mm. Prior to surgery seven years later at age 21 it was herniated 8.5mm. The largest documented case I could find over the Internet was 9mm.