The following post is taken from the American Hearing Research Foundation. The author is Timothy C Hain, MD.
What is Chiari Malformation?
The Chiari malformation, also known as the Arnold-Chiari malformation, is a relatively common syndrome involving displacement of the cerebellar tonsils below the level of the foramen magnum. Associated with the Chiari malformation may be hydrocephalus (accumulation of fluid within the central cavities of the brain), spina bifida (a malformation of the spinal cord), and syringomyelia (accumulation of fluid within the spinal cord). In most instances, symptoms present in middle age.
What Causes Chiari Malformation?
The Chiari malformation is generally thought to be present from birth. However, in some instances, mild Chiari malformations may be caused by low cerebrospinal fluid (CSF) pressure. A closely related condition called basilar invagination may also be congenital or acquired from arthritis.
Saggital midline MRI scanFigure 1: Saggital midline MRI scan of person with Chiari-I malformation showing displacement of cerebellar tonsil below the upper margin of the foramen magnum
How is Chiari Malformation diagnosed?
The definitive method of diagnosis is with a sagittal T1 magnetic resonance imaging (MRI) scan of the posterior fossa of the skull, which documents the typical downward herniation of the cerebellar tonsils (see Figure 1). A displacement of greater than 5 mm below the foramen magnum is deemed significant. In some instances, MRI CSF flow studies are used to decide if a displacement is causing any damage.
Recent studies have evaluated the usefulness of somatosensory evoked potentials (SEP) in the evaluation of Chiari malformation (Vidmer, et al., 2011; Sala et al., 2011; Boor 2004, Henriques 2006). These studies found abnormal SEPs to correlate with symptomatic Chiari malformation, suggesting that this is a useful tool to monitor progression of the disorder.
What are the Symptoms of Chiari Malformation?
Symptoms suggestive of Chiari include posterior headaches, dizziness and ataxia, or poor coordination (especially associated with straining), fainting with a cough, and weakness or numbness. A review of the otologic manifestations of Chiari in 16 patients indicated that 81% reported episodic aural fullness, 81% tinnitus, 69% vertigo, and 56% fluctuating hearing. Headache was also common (about 80%). These symptoms overlap with those of Meniere’s disease as well as to lesser extent, migraine (Sperling et al, 2001)
Signs of a significant Chiari malformation often include downbeat nystagmus, poor visual pursuit for age, and alternating skew deviation. Occasionally patients will have sensorineural hearing loss Heuer et al., 2008).
A few individuals with the Chiari malformation develop progressive neurological symptoms. These may include unsteadiness, vertigo, headache, weakness or numbness.
How is Chiari Malformation Treated?
The only effective treatment is surgical treatment, and consists of a procedure called suboccipital decompression. In essence, this procedure involves removal of bone from the back of the skull to make more room for the brain. This treatment is best deferred until symptoms are significant.
How Might Chiari Malformation Affect My Life?
Persons with the Chiari Malformation can often live out a normal life. Only rarely does the feared progressive neurological deterioration occur. We think it best for persons with the Chiari malformation be particularly careful to avoid head injuries. Contact sports such as football may be ill advised.