MODEL RELEASED. Cerebral shunt. X-ray image showing the placement of a ventriculo-atrial shunt from an arachnoid cyst in the brain of a 17-year old woman. The shunt drains fluid from the cyst (centre) down through her neck (lower right) toward the right atrium of the heart. Once at the heart the fluid enters the bloodstream. Arachnoid cysts are pockets of cerebrospinal fluid (CSF) covered by arachnoid cells and collagen. As the cyst grows it may block the normal flow of CSF from the brain resulting in hydrocephalus. Arachnoid cysts are found in about 1 in 2000 people, although they may often be asymptomatic and relatively benign.