LOS ANGELES, CA (Catholic Online) - The large mass on her back was identified to be part of an identical twin that had failed to develop and had been enveloped into the body of its sister. Exploratory examinations later revealed that other parts of the unborn twin, such as a breast and an arm which included a shoulder blade and two fingers.

A parasitic twin (also known as an asymmetrical or unequal conjoined twin) is the result of the processes that produce vanishing twins and conjoined twins, and may represent a continuum between the two. Parasitic twins occur when a twin embryo begins developing in utero, but the pair does not fully separate, and one embryo maintains dominant development at the expense of the other. Unlike conjoined twins, one ceases development during gestation and is vestigial to a mostly fully formed, otherwise healthy individual twin. The undeveloped twin is defined as parasitic, rather than conjoined, because it is incompletely formed or wholly dependent on the body functions of the complete fetus. The independent twin is called the autosite.

Professor Baogan Peng, of the General Hospital of Armed Police Force in Beijing was among the first to be notified of the girl's condition. Writing in the journal BMJ Case Reports, Professor Peng said "Based on physical examination and imaging findings, a diagnosis of fetus in fetu was made preoperatively."

The fetus in fetu is a highly rare condition that affects only one in five million live births. It is a condition where the malformed fetus is found in the body of its twin.

In the majority of cases, 80 percent, the fetus is found in the abdomen. There have been reports of the parasitic twin being found in the skull. This case was the first instance of the condition being found in the back.

The girl also suffered from diastematomyelia, which is a congenital disorder in which the spinal cord is split.

Dr. Peng, an expert in spinal surgery, said doctors successfully removed the parasitic twin, despite there being no clear way of separating them. A later analysis also found digestive tract lining in the tissue.

© 2012, Catholic Online. Distributed by NEWS CONSORTIUM