there was a dutch guy that did this in 1965, Bart Huges.   strange thing is, after a particularly 'energetic' meditation I got a slight dent in my forehead, as if the connective tissue at that spot had melted. it has deepened quite a bit through the years and is now so deep that i guess skullthickness has thinned too.  It begins to look like his one.   I remember in my youth this guy was talked about as the summum of crazyness. He died at the age of 70 in 2004