Debbie
My son, who is 11, was also just diagnosed with an arachnoid cyst. The neurosurgeon diagnosed him with "Dandy Walker syndrome". It is a congenital problem in his brain that causes the cerebrospinal fluid to collect in the arachnoid layer of his brain. Where is his cyst? My son's was in the cerebellar region. It is not big enough right now to drain, but he will need MRI's every 6 months to check on it's progress and may need a shunt to drain it. You can email me if you would like more info.