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| Chiari Malformation |
Chiari I Malformation
Definition: Chiari I Malformation
(CMI) is one of several identified malformations of the
hindbrain, which consists of the cerebellum, pons, and
medulla oblongata. Additionally, the back part of the
skull (posterior fossa) is too small, and the cerebella
tonsils (part of the cerebellum) are pushed downward through
the hole at the base of the skull (the foramen magnum).
Chiari I malformation is typically defined as a 3 to 5
mm herniation of the cerebella tonsils below the foramen
magnum. The result can include compression of the brain
stem, the part of the brain which controls involuntary
body responses such as the heart beating and breathing;
compression of the cranial nerves; and disruption of the
flow of cerebrospinal fluid.
Treatment: Symptoms vary from patient to patient in severity, duration and location. If symptoms become life
threatening or the quality of life poor, surgery may be needed to relieve pressure at the back of the brain.
The simplest form of this surgery involves removal of part of the bone in the back of the skull (suboccipital
craniectomy). Additional surgery may be required if the removal of bone does not relieve enough pressure.
Other findings such as a retroflexed odontoid process, basilar invagination, and abnormalities of the cervical
vertebrae must also be considered prior to surgical intervention. It should be noted that the degree of herniation
does not dictate whether or not the patient should have surgery. A patient could have a very small herniation, but
severe symptoms as a result of an associated disorder such as hydrocephalus, which requires surgery. On the other hand,
a patient could have a larger herniation and not have any symptoms, in which case surgery is not indicated.
Symptoms: Please see our page for a comprehensive Symptom List
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