In the back of your brain, there are tonsils, called cerebellar tonsils, that can descend through the base of the skull (foramen magnum). If there is only a slight tonsillar protrusion thru the foramen magnum and the patient does not exhibit typical symptoms of Chiari, the patient may be diagnosed as having cerebellar tonsil ectopia – sometimes considered a milder form of Chiari malformation. A final clinical diagnosis is made only after a neurologic exam and detailed history is taken.
Chiari malformation is a congenital anomaly of the cerebellum and brainstem. Although four types have been described, types I and II are more common. Type I is identified by protrusion of cerebellar tonsils through the foramen magnum, down to the C1 or C2 level of the cervical spine. It may or may not be associated with syringomyelia/hydromyelia. Type II is the most common type of Chiari malformation, always associated with myelomeningocele. The remainder of this summary describes Chiari type I malformation.
Presentation usually begins in adulthood, from ages 20 to 50 years. The most common symptoms are a headache or neck pain, aggravated by coughing, sneezing or extension of the head and neck. Other symptoms may include imbalance or distorted vision. Less common are altered sensation or weakness of the arms and/or legs, which are typically associated with hydromyelia.
MRI scan of the brain and/or cervical spine is the diagnostic test of choice to confirm Chiari malformation. Hydromyelia/syringomyelia can also be identified by MRI scan. Various degrees of Chiari malformation or tonsillar ectopia can be identified on the MRI scan.
The only effective treatment for Chiari malformation is surgery. The most common surgical procedure is suboccipital craniectomy to decompress the cerebellar tonsils (surgical opening of the bony compartment of the back of the head) with laminectomy of C1 and/or C2 to decompress the cervical spinal cord. The opening of the dura (lining of the brain and spinal cord) with dural grafting to expand the cranial and upper cervical spine space completes the procedure. Sometimes the surgeon will elect to not open the dura. The procedure is performed under general anesthesia and usually lasts two to three hours.