Hydrocele in the scrotum of a 60 year old male patient. A hydrocele is a fluid-filled sac in the scrotum that causes swelling. It may affect one side of the scrotum or both sides. They?™re more common in infants but can also occur in adulthood. In adults the causes may be due to scrotal injury or inflammation. Hydroceles are usually not dangerous but they can be treated by minor surgery to drain the fluid if they cause discomfort or distress.