Chiari Malformation
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 result from low cerebrospinal fluid (CSF) pressure. A closely related condition, basilar invagination may also be congenital or acquired from arthritis.
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| Figure 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 saggital T1 magnetic resonance imaging (MRI) scan of the posterior fossa, 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.
What are the Symptoms of Chiari Malformation?
Symptoms suggestive of Chiari include posterior headaches, dizziness and ataxia (especially associated with straining), fainting with a cough, and weakness or numbness. A recent 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 pursuit for age, and alternating skew deviation. Occasionally patients will have sensorineural hearing loss (Hendrix, 1992).
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.
Research Studies on the Chiari Malformation
At the American Hearing Research Foundation (AHRF), we are particularly interested in projects that might lead to improved management of the hearing symptoms that may result from the Chiari malformation. Click here if you would you would like more information about contributing to the AHRF's efforts.
References
- Ahmmed, A. U., I. Mackenzie, et al. (1996). "Audio-vestibular manifestations of Chiari malformation and outcome of surgical decompression: a case report." J Laryngol Otol 110(11): 1060-4.
- Albers, F. W. and K. J. Ingels 1993). "Otoneurological manifestations in Chiari-I malformation." J Laryngol Otol 107(5): 441-3.
- Chait, G. E. and H. O. Barber (1979). "Arnold-Chiari malformation--some otoneurological features." J Otolaryngol 8(1): 65-70.
- Hendrix, R. A., C. K. Bacon, et al. (1992). "Chiari-I malformation associated with asymmetric sensorineural hearing loss." J Otolaryngol 21(2): 102-7.
- Johnson, G. D., R. E. Harbaugh, et al. (1994). "Surgical decompression of Chiari I malformation for isolated progressive sensorineural hearing loss." Am J Otol 15(5): 634-8.
- Samii, C., E. Mobius, et al. (1999). "Pseudo Chiari type I malformation secondary to cerebrospinal fluid leakage." J Neurol 246(3): 162-4.
- Sperling NM, Franco RA, Milhorat TH. Otologic manifestations of Chiari-I malformation. Otology Neurotol 22:678-681, 2001
- Stovner, L. J. (1993). "Headache associated with the Chiari type I malformation." Headache 33(4): 175-81.
- Weber, P. C. and S. P. Cass (1993). "Neurotologic manifestations of Chiari 1 malformation." Otolaryngol Head Neck Surg 109(5): 853-60.
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