Chiari malformation (ACM, CM) is a rare condition where the lower part of the brain (the cerebellar tonsils) has herniated down in to the spinal cord area.
Hans Chiari first identified the disorder in the 1890’s. A colleague of Professor Chiari, Dr. Arnold, later contributed to the definition of the condition, and the students of Dr. Arnold suggested the term "Arnold-Chiari malformation" to be the full term for the condition.
There are 2 main types -Type I and Type II. Tyoe 2 being more serious and is associated with Spina Bifida. We then have Type III and IV, however these are very rare.
The cause is unknown, believed to be primarily a congential condition, although there have been some reported cases of an acquired form.
This condition affects people of all ages, however is usually diagnosed in children and adults in late 20’s – early 30’s.
Classic definition involves the length of the herniation (>3-5mm).
Research has shown little correlation between length of herniation and symptoms; focus now on flow of cerebrospinal fluid (CSF); malformation blocks normal flow. This can also lead on to a secondary condition, syringomyelia, in some people.