An 11-year-old girl in China had a life-changing procedure recently when doctors discovered that she had a third arm emerging from her back.

Doctors were stunned to discover that she had a shoulder blade and arm with two fingers, as well as some breast tissue growing from her back.

The girl was afflicted with an extremely rare condition called fetus in fetu. The condition affects just one in 5 million births. Researchers believe that the arm belonged to an unborn twin sister who was growing inside of her. The girl was the second child in a family that had not previously reported twin births or birth abnormalities.

As rare as the situation is in itself, this unnamed girl's particular case is extremely unheard of. Normally, when fetus in fetu is discovered, it is because of a growth on the stomach; that occurs in 80 percent of cases. Such growths have also been discovered on the skull, sacrum, scrotum, and mouth. Her case was the first time organs from a twin had been discovered growing from a person's back.

In addition to her literally parasitic twin, the girl was discovered to have another rare condition called diastematomyelia. This condition is a congenital disorder, or a disorder that appears at or shortly after birth, in which the spinal cord is split. It is unclear by the report whether doctors also addressed that separate disorder.

Fortunately, Baogen Peng, the author of the case report published in the British Medical Journal, said that doctors were able to successfully remove her twin. This feat was made all the more astonishing because doctors had no clear way to separate them.

Peng and his colleague Duanming Li reported that doctors also found a digestive tract among the removed tissue.

The case report did not state how the girl was doing following her surgery.