'Fetus in Fetu' is a rare phenomenon, also known as baby within a baby that doctors say results in the absorption of one's embryonic twin.
This week, Greek doctors had removed what they believe was an embryonic twin absorbed into the abdomen of a 9-year-old girl while they were both in the womb. The removed 2-inch-long embryo was a fetus with a head, hair and eyes, but no brain or umbilical cord.

'Fetus in Fetu' occurs in the first month of pregnancy while still developing in the womb. What it happens is that one twin "enters into the other through the umbilical cord where it acts as a parasite. After birth, it is an abdominal mass. However, the fetus does go through a developing phase at the beginning but it never fully develops. Structures like an axial spine and the beginnings of organs do develop. But the parasitic twin is neither a true twin nor a conjoined twin.

Before being removed, this mass palpates in the stomach. On images, it appears as a calcified structure but you can actually see the bone structure and axial configuration of the spine. The mass doesn't represent a problem to the host and these children are otherwise perfectly healthy. After the removal, the host child quickly recovers with no long-term side effects.

The girl, whose name has not been released publicly, had a swelling on the right side of the abdomen but the doctors didn't suspect this tumor was an embryo. She is recovering well after the removal.

Fetus in fetu is very rare. It occurs only once in every 500,000 people.