I look up sick shit all the time and have read about basically every kind of infection/infestation/abnormality you can have. And I have NO CLUE what the fuck this is. Anyone?? PLEASE!!! It's driving me nuts!
Probably got injured/attacked or something, lost a chunk of his head and didn't get it checked, got infected and this is the end result.
Also, He's probably been dead for awhile now.