Yamini Karanam, a PHD student at Indiana University, was undergoing surgery for a suspected tumour when the doctors found an embryonic twin.
In a shocking discovery, doctors in the US have found an embryonic twin complete with bone, hair and teeth in the brain of a 26-year-old Indian woman, who was undergoing surgery for a suspected tumour.
Yamini Karanam, a PHD student at Indiana University, sought medical help last September after she started having trouble reading and talking.
Ms Karanam was diagnosed with pineal tumour after doctors spotted what they thought was a cyst on her pineal gland, a tiny pea-like structure in the centre of the brain, The Washington Post reported.
At one point Ms Karanam, who is from Hyderabad, could barely eat and pain ran from her head throughout her body.
In March this year, Ms Karanam connected with Hrayr Shahinian, a doctor performing radical 'keyhole' brain surgeries at the Skullbase Institute in Los Angeles.
Dr Shahinian made a tiny incision in the back of Ms Karanam's head, then strung an endoscope into her skull and through a natural channel in her brain to the site of the suspected tumour.
However, Dr Shahinian was shocked to discover that the tumour was actually a teratoma: a clump of bone, hair and teeth.
Dr Shahinian successfully removed the teratoma and now expects Ms Karanam to make a full recovery.
Ms Karanam told NBC 4 that she was stunned to learn that her tumour wasn't just a lump of cells, but her "evil twin sister who's been torturing me for the past 26 years."
Some doctors believe teratomas are twins that never quite develop and are instead absorbed into the surviving baby's body.