What Causes Persistent Runny Nose?

I have running nose for years.The doc suspected there is a leak from my brain,hence the moucus (water from the nose )was sent to the lab to confirm if it true.The result is negative.Nex have to do a CT brain scan which I am really frightened.Can u please help me?The running nose is very active morning and at home.If I am out from home esp on hols,I seldom have running nose.



Thank You