Chiari malformations

Chiari malformations are distortions at the base of the brain that may be present at birth or can form throughout life.  The cerebellum, the part of the brain that controls balance and coordination, sits just above the opening at the bottom the skull (the foramen magnum) through which the brainstem passes to the spinal cord.  In some people, the bottom edge of the cerebellum starts to sink down through the foramen magnum, where it can become pinched against the brainstem.  Although many patients notice no symptoms, this can sometimes cause intermittent or continuous dizziness and imbalance as well as other symptoms. 

Basket of Puppies, CC BY-SA 3.0 <https://creativecommons.org/licenses/by-sa/3.0&gt;, via Wikimedia Commons

There are a few different types of Chiari.  We’ll concentrate here on the type called Chiari I, which develops and causes symptoms that generally begin after childhood. Headache and neck pain are common.  Balance can be poor, with dizziness, hearing loss and tinnitus.  Sleep apnea can result, with insomnia and morning headaches. 

The dizziness results from nystagmus, a vertical scrolling of the eyes.  This can often be brought out by lying down flat on the back with the chin tipped up.  In this way it is similar to benign positional vertigo. However, the nystagmus will usually continue unchanged as long as the head remains in this position, while in BPPV the nystagmus reaches a peak and then subsides over less than a minute.  To an observer, the nystagmus is vertical—the eyes seem to scroll or beat in a downward direction, called downbeat nystagmus.  Because the nystagmus indicates that  the brainstem is being compressed, it is best to leave testing to a physician.  The nystagmus can be recorded by VNG testing.  A sleep study can pick up any associated sleep apnea.

If the examination suggests Chiari malformation, it can be diagnosed by an MRI of the brain.  Once found, the underlying cause can sometimes be identified and treated. For example, leaks of spinal fluid in the low back can sometimes cause the syndrome, and it can improve when the leak is repaired.  In other cases, surgery to decompress the cerebellum and enlarge the opening to the foramen magnum can be done.   Milder cases can be managed without surgery.

Published by Vertigone

I translate the medical world of dizziness for non-medical people

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