Sixteen year old girl went in to have her appendix removed and doctors stumbled upon a tiny brain instead.

A team of doctors in Japan came across a 10 centimeter wide tumor with a 3 centimeter wide brain inside with clumps of hair and a thin skull bone. The brain was found to be a smaller version of the cerebellum which sits just under the brains two hemispheres.

About one fifth of ovarian tumors contain foreign tissue like hair, teeth, cartilage and fat. The theory is that they arise when immature egg cells turn rogue, producing body parts. The tumors are most diagnosed in women's reproductive years.

While many tumors do develop other tissues like fat and hair, it is very unusual for them to form into brains. The brain that was found in the Japanese girl developed to send electric pulses between neurons like a regular brain.

While the girl didn't have symptoms, there have been cases where women experience personality changes, paranoid thoughts, confusion, agitation, and memory loss. Symptoms tend to arise when the immune system recognizes brain cells as foreign and launches attacks.