There's a book by Philip K. Dick (one of my favorite authors) in which one of the characters is a little girl who's twin brother was born inside of her, and lives there as a parasite, communicating with her telepathically.
Bizarre, right?
Cut to reality:
"Doctors at Chimkent Children's Hospital in Kazakhstan originally believed Mourat Zhanaidarov was suffering from a cyst.
But during surgery, they discovered he was in fact carrying the dead foetus of his twin brother.