What Causes Fluid Retention On Forehead After An Accident?

I am a 48 year old female 5'2 150 pounds. I was injured in a car accident 1 year ago that resulted in a TBI which I am currently being treated for. As a child (2 years) i fell down stairs and had a collection of fluid on my forehead. after 2 weeks my mother became alarmed and brought me to a doctor. He said i didnt have a concussion. what would the collection of fluid have been. This event has been brought up in my therapy, any ideas? My mother doesnt remember the details.