Arnold Chiari Malformation
The Common Vein Copyright 2010
Definition
Chiari malformation (aka Arnold Chiari malformation) isusually a congenital malfrmation but may be seen in conditions that have ligamentous laxity such as Ehlos- DAnlos Syndrome where occipitoatlantoaxial hypermobility results in structural changes of the cerebellar tonsils by positional alteration characterized by downward displacement of the cerebellar tonsils through the foramen magnum often resulting in hydrocephalus. There are 4 types described.
Functionally the obstruction causes elevated intracranial pressure thus causing a clinical presentation of fatigue, headaches, nausea and vomitting, and motor dysfunction caused by involvement of the cerebellum. In childhood, the patients may be asymptomatic.
The diagnosis is initially based on clinical presentation and then confirmed by imaging, usually by MRI when the tonsils project more than 5mms beyond the foramen magnum. CT is also useful, and prenatal ultrasound is used to diagnose the entity in utero.
Treatment is surgical sometimes through decompression by laminectomy of the proximal cervical vertebra and or by shunt decompression.
Chiari Type 1 |
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Note the malposition of the compressed cerebellar tonsils beyong the foramen magnum but no obvious associated hydrocephalus. Courtesy James Donnelly MD Uploaded 23167 |