There are several types of Chiari malformations. Previously referred to as "Arnold-Chiari malformations," they describe abnormal development of certain parts of the nervous system. The most common type is the Chiari 1 malformation. When the lower part of the brain is "cramped," it can be pushed downward toward the spinal canal. This may disrupt the flow of cerebrospinal fluid in the head or the spinal cord. Symptoms can include pain in the back of the head and neck, numbness and tingling in the hands, or even clumsiness. Treatment involves decompression, which essentially makes more room for the crowded brain tissue and restores normal flow of cerebrospinal fluid.