At the top of my forehead on the left side, just below the hairline, I have a two-inch long flat/indented part of my skull that seems to have a small gap in the middle, like a line running through it, parallel to the hairline, that I can push the tip of my finger down into. It has been like this for quite a while, with no pain or other symptoms, but it seems to gradually be getting bigger. Is this a cause for concern?