Arachnoid cysts are a collection of cerebrospinal fluid (CSF, the fluid that covers the
brain and spinal cord) between two layers of tissue called the arachnoid. They are thought to be present from birth in the large majority of patients. They can occur in any location within the brain. They are often incidental findings with no symptoms and with no consequences. However, when they do cause symptoms, that could include headaches, seizures, and in some rare instances psychiatric problems.