The Chiari Malformations

The Chiari (kee-ar-ee) malformations are a congenital abnormalities of the posterior fossa (base of brain where the spinal column joins the skull). This usually causes a protrusion of the cerebellum through the bottom of the skull (foramen magnum) into the spinal canal. This results in a poor circulation of  cerebrospinal fluid from brain to spinal cord. See pictures below.

          

History
Professor Hans Chiari was a German pathologist who first described these abnormalities of the brain at the junction of the skull with the spine in 1890. Another doctor, Arnold, later added to the type II description, hence the name "Arnold-Chiari Malformation". Of the four classifications of Chiari, only two types of the malformation have practical importance, commonly referred to as Chiari type I and Chiari type II.

Description
The Chiari I Malformations are a result of the smallest herniation of an otherwise normal hindbrain. The tonsils would normally be round but often become elongated as they protrude down the spinal canal. Diagnosis can be difficult because not all patients will have the classical sign of deeply herniated tonsils.

The Chiari II is usually found in children with spina bifida or myelomeningocele. Not only is part of cerebellum unusually low and lying below the bottom of the skull, but the brain stem can be malformed in several ways. This malformation is part of a much greater malformation of the nervous system. This is the type of Chiari malformation that is correctly referred to as "Arnold Chiari" malformation.

Symptoms
Usually symptoms of Chiari malformations do not appear until early adulthood but can occasionally be seen in young children. Some common symptoms include headaches, neck pain, dizziness, vision problems, balance problems and muscle weakness. Other symptoms include difficulty swallowing, frequent gagging and choking and, in some cases sleep apnea may be present. 

Treatment
Surgery to enlarge the opening of the posterior fossa of the skull is often recommended for patients. Techniques are quite diversified amongst neurosurgeons and patient responses vary greatly. A successful surgery will alleviate pressure on the neural elements and may result in an improvement of symptoms.