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
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.
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.
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.
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.
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.