Do people become famous because their heads are large, or does celebrity actually cause the head to enlarge?

Over in last night's "American Idol" thread, Trooper York wrote:

The girl that sang "At Last" has an extremely big head. Which is very good since most popular actors have heads out of proportion to their bodies.

This reminds me of something that I read a while back in Tina Brown's excellent book "The Diana Chronicles":

What struck me at lunch was how much celebrity itself had transformed Diana's appearance. I have come to think that being looked at obsessively by people you don't know actually changes the way your face and body are assembled — not just in the obvious ways of enhanced fashion sense or tricks of charm and self-possession, but in the illusion of size. The heads of world-class celebrities literally seem to enlarge. Hillary Clinton's, for instance, has grown enormously since she was the mere wife of the governor of Arkansas. It nods when she talks to you like a balloon in the Macy's Thanksgiving Day parade. The years of limelight so inflated the circumference of Jackie O's cranium, it seemed her real face must be concealed by an oversized Halloween mask. If you looked into her eyes, you could see her in there somewhere, screaming.