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| Welcome to Chiari Connection International |
Note: There is NO affiliation, whatsoever, between this site , which is Chiari Connection International
and the site calling itself Chiari Connection.
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 cerebellar 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 5mm or even higher herniation of the cerebellar tonsils
below the foramen magnum. However, there have been a significant number of diagnosed cases with no herniation.
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.
Associated Conditions: Other conditions including hydrocephalus, syringomyelia, seizure disorder, scoliosis,
tethered cord syndrome, craniocervical instability, and Ehlers-Danlos syndrome can also be present in a patient
diagnosed with Chiari I malformation. In addition to measuring the degree of herniation of the cerebellar tonsils,
some surgeons look for the presence of a retroflexed odontoid process, basilar invagination, the presence of CSF
flow in the posterior fossa, the volume of the posterior fossa, and the presence of arterial and/or venous
malformations in the brain and cervical spine. Of note, Chiari II (Arnold-Chiari Malformation) is typically associated
with Spina Bifida and myelomeningocele.
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.
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