I can see why your doctor is ordereing the MRI.
One possibility is that every since you were born, your skull suture was not closed all the way. For example, a baby has a skull suture that is open, but as they get close to about 18 months or so, if I remember correctly, it closes. The purpose of the open suture in the skull is for the birth process, so the skull will be flexible enough to get through the birth canal. Closure after that time is important to prevent damage to the gelatenous (like gelatin) brain.
I looked through research and the regular internet and could not find any instance of a suture staying open. There is a condition where they close to early in an infant, that causes damage because there is not quite enough room for the brain to grow, but I could find nothing about this.
I have an article about the sutures on the skull so that you can see if the indentation that you are speaking about appears to be along the line of one of these.
So I'm sorry, no definate answer. Take very good care of yourself, and I hope everything turns out okay.