In Type I Chiari malformation, the lower part of the cerebellum, called the cerebellar tonsils, protrudes through the opening at the base of the skull (the foramen magnum) into the upper spinal canal. This can cause obstruction of CSF flow and compression of the brainstem.
Symptoms of Type I Chiari malformation can vary widely among individuals and may include headaches, neck pain, vertigo, balance and coordination problems, ringing in ears or hearing loss, vision problems, sleep disturbances, and weakness in arm or legs.