A condition whereby a part of the brain called the cerebellum bulges through the natural opening of the base of the brain where it joins the spinal canal, causing pressure upon the exiting brainstem and disrupting the flow of cerebrospinal fluid (the fluid in which bathes the brain and spinal cord)

Can be associated with syringomyelia (cyst within the central part of the spinal cord)

Symptoms such as headaches, altered arm/leg sensation, weakness or incoordination of hands and feet can occur

Surgery can take the form of removal of a bar of bone behind the bulging cerebellum with reconstruction of the lining of the brian (dura) to allow for restoration of normal flow of cerebrospinal fluid