Finding out that your brain tumour isn't actually a brain tumour is usually good news, but in this case we're not so sure.
Last year 26-year-old Yamini Karanam began having trouble with her comprehension and understanding people around her and decided that she needed medical attention. When she went to her doctors however, they weren't sure what to do because they weren't sure what was wrong.
So Karanam hunted down a specialist in Los Angeles who stuck a camera in her brain and found out that the tumour wasn't a tumour at all, but a teratoma that was in fact her embryonic twin who had been in her skull since she was born.
Karanam underwent surgery and the mass/her twin was removed, and she's expected to make a full recovery (apart from the nightmares she's probably going to have for the rest of her life).