Doctors have discovered an embryonic twin, complete with bones, hair and teeth, embedded in the brain of a 26-year-old Indian woman who was going under the knife for a suspected tumor, reports the Times of India.

Yamini Karanam, a PHD candidate at Indiana University, went to her doctor last September after she began to have trouble talking and reading. At one point the young woman could barely eat and was experiencing full-body agony and blinding headaches.

Karanam was diagnosed with a pineal tumour after doctors caught what they initially believed was a cyst on her pineal gland, a tiny pea-shaped mass in the center of the brain.

In March Karanam met with Hrayr Shahinian, a doctor specializing in radical ‘keyhole’ brain surgeries at Los Angeles’ Skullbase Institute. Her friends held a fundraiser to help pay for the operation.

Shahinian made a minuscule incision in the back of Karanam’s head, then threaded an endoscope into her skull and through a channel in her brain to the location of the suspected tumor.

What followed next stunned the doctor:  the suspected tumor was actually a teratoma: a chunk of bone, hair and teeth. Teratomas are believed by some medical professionals to be twins that do not fully develop and are instead absorbed into the surviving twin’s body.

Shahinian successfully excised the teratoma; he expects Karanam to make a full recovery. “This is my second one, and I’ve probably taken out 7,000 or 8,000 brain tumors,” Shahinian told NBC 4.

Karanam also 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.”