broke spark plug "head" in housing
 

hi gang... as i was removing my trailing spark plug off..the spark plug broke off!!! the 4 strap "ground" threaded hollow head is still threaded in the housing, anyone have any suggestions on how to "extract" it out?? im thinking about using a hammer-in style extractor...theres nothing i can drill as the head that stuck in there is hollow

any tips please!!!!!!!!!!!!!!!!!!

thanks

some kind of screw extractor is the only thing I can think of.