About that lump in your abdomen—it was likely your unborn twin. So a teenager in India was told after surgeons removed "hairy cheesy material" from her abdomen two years ago, LiveScience reports. More precisely, the mass measuring 14 by 6 by 4 inches contained apparent ribs and vertebrae along with "multiple teeth and structures resembling limb buds," per an analysis in BMJ Case Reports. The 17-year-old had complained about a growing abdomen lump that sometimes caused her pain or the feeling of being full. After a CT scan, doctors diagnosed her with fetus in fetu, a rare condition in which an oddly developed fetus is found inside a person's body. Why it occurs is unclear.
Scientists say it's probably one identical twin absorbing another during early pregnancy, per Arizona State University, or a kind of tumor called a teratoma that's comprised of body tissues like muscle, bone, and hair. Fewer than 200 instances are on record, and only 7 in people who are 15 and older. In the Indian teen's case, doctors successfully removed most of the mass but had to leave some tissue that was tightly bound to blood-supplying vessels. That raises the chance of cancer and means she must be checked annually. But for now, the report says she's fine: "I was much worried about my abdominal lump," she says. "After operation I am feeling very well … and my parents are also very happy." (Read more medical condition stories.)