A mass of "hairy cheesy material" has been removed from a teenager's abdomen - all that was left of her twin that failed to grow into a person, doctors say.
The 17-year-old Indian girl went to the doctor in 2017 five years after a lump began growing in her abdomen, according to this month's issue of journal BMJ Case Reports.
She was experiencing "on and off" pain and often felt full when she'd hardly eaten anything. Aside from the lump, she was in perfect health.
"This abdominal lump was firm to hard in consistency, its surface was irregular, margins were ill-defined and it was not moving with respiration," the report said. "It was not possible to conclude a final diagnosis."
So they did a scan and found a mass of tissue and bony-like substance almost the size of a newborn baby.
"It was showing fat density areas, soft tissue and multiple calcified density components of various sizes and shapes resembling the shape of vertebrae, ribs and long bones."
When they took it out, they found it contained "hairy cheesy material, multiple teeth and structures resembling limb buds". Some of it was left behind over fears removing it would cause more problems than it would solve.
The primary diagnosis is fetus in fetu, an incredibly rare condition that's only been recorded a couple of hundred times in history. It's believed it happens when one identical twin absorbs the other while they're still in the foetal stage - otherwise known as a parasitic twin.
- Woman's bizarre 'floating kidney' problem fixed
- What eating world's hottest chilli pepper can do to you
- Man seals his eye shut after mistaking superglue for eye drops
Another theory is that it's a teratoma - a tumour made up of several different types of cells.
Whatever it was, two years on, the teenager is doing well. She has to check in each year to make sure the material left behind isn't turning cancerous.
"My abdomen is now flat and my parents are also very happy," she said.