A Teen Had A Twin In Her Abdomen, A Case Study Reports, & Here’s How Common That Is

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If you're like me, and you're fascinated by unusual medical conditions, you've likely heard of parasitic twins, teratomas, and fetus in fetu (FIF). These conditions occur in twins when one fetus absorbs the other in utero. In some cases, the absorbed twin continues to develop, growing teeth, hair, and sometimes even bones. A new case study reported that one teen lived with a twin inside of her for 17 years, according to Gizmodo. The tissue was removed two years ago, and the teen is now doing just fine.

The teen, who lives in India, had been seeing doctors five years for a lump in her abdomen, according to the case study published in the journal BMJ Case Reports. The lump continued to grow and press on her organs, and when doctors removed it they discovered something surprising. "The contents of the tumor consisted of hairs, mature bones, and other body parts," the study said.

The teen was diagnosed with FIF, which is slightly different than a teratoma as an FIF contains vertebrae, organs, and limbs. A teratoma does not contain vertebrae. In addition, according to the Mayo Clinic, teratomas are usually found in the ovaries and testes, whereas FIF can present in various areas in the body. The study explained that most cases of teratomas, parasitic twins, and FIF are detected in infants and young children. There are only seven known cases in the world where the absorbed twin has lived off of its host sibling for more than 15 years, making it a very rare medical condition.

BMJ Case Reports 2019

"There are two theories for the development of FIF. One is parasitic twin theory in which parasitic malformed fetus formed inside the body of its host twin and share common blood supply. The parasitic twin is anencephalic with lack of many internal organs and it usually dies before birth," the study reported. "The other theory is that FIF is a highly differentiated form of teratoma."

While the majority of FIF cases are identified shortly after birth, the oldest person diagnosed with FIF was 47, the study noted. According to a report published in the journal Surgery, a 47-year-old man was found to have an FIF that contained hair, bones, vertebrae, and ribs. Unlike the case of the 17 year old, his parasitic twin did not continue to grow or cause any complications.

In another case, a 36-year-old man with a swollen abdomen was rushed to the hospital with shortness of breath. When doctors operated, they discovered the man had FIF. "To my surprise and horror, I could shake hands with somebody inside. It was a bit shocking for me," ABC News quoted Dr. Ajay Mehta of Tata Memorial Hospital in Mumbai, India, as saying.

A second unnamed doctor added, "[Dr. Mehta] just put his hand inside and he said there are a lot of bones inside. First, one limb came out, then another limb came out. Then some part of genitalia, then some part of hair, some limbs, jaws, limbs, hair."

In the most recent case, the teen will need consistent follow-up care, as doctors were not able to remove all of the FIF tissue, and there is a possibility that some of the cells could continue to grow.