<qa>  What is the protective fluid that fills the empty spaces around the brain and spinal cord?Cerebrospinal fluid CSF is the protective fluid that fills the empty spaces around the brain and spinal cord. CSF is naturally produced and absorbed, but with age abnormal metabolism and clearance of amyloid beta proteins can lead to accumulation of these proteins, resulting in plaque formation, a leading contributor to the progression of Alzheimers disease AD. The shunt treatment is designed to drain CSF with these toxic elements from the skull and allow replenishment of normal CSF. This clinical study is designed to determine if this device will stop or slow the progression of Alzheimers disease. 