Doctors caring for a baby boy in Mumbra, India, were shocked to discover he was "pregnant" with his own twin brother.
During a routine scan of his mother during pregnancy, radiologist Dr. Bhavna Thorat spotted an abnormal mass on the baby. When the baby was born, Dr Thorat performed a scan of the newborn.
The scan revealed a 7-centimeter growth inside the baby's abdomen, thought to be the baby's twin, which had been enveloped in the womb.
The growth appeared to be a case of "fetus in fetu", an extremely rare abnormality where a fetus becomes enveloped by its own twin. After identifying the mass, surgeons successfully operated on the newborn, removing the 7-centimeter-long fetus from his abdomen.
The baby and his mother were moved to Titan Hospital in Thane after surgery, where they are both recovering well.
Less than 100 cases of "fetus in fetu" have ever been recorded worldwide, with the abnormality happening in only one per 500,000 births.
One theory on how it happens suggests that the "parasite" twin begins as a normal fetus, sharing a placenta with its sibling. Early during pregnancy, however, the host twin envelopes the other twin. The twin that has been enveloped becomes a "parasite" as it uses the host twin's blood supply in order to survive.
In cases of fetus in fetu, the "parasite" twin lacks the organs it needs to survive outside of the twin and threatens the life of the host it inhabits, as both twins try to get the nutrition they need from a single umbilical cord.
Usually, the twin has no brain or vital organs, however in this case the doctors reported seeing a brain within the parasitic fetus.
"It was inside a fetal sac of the newborn," Dr Thorat, who took the initial scans, said to the Daily Mail. "I could see bones of the upper and lower limbs of the fetus."
"The unique thing about it was I could see a tiny head with the brain inside," Thorat added. "However, this parasitic twin didn’t have a skull bone."
With the mass removed, the surviving twin is doing well and no problems have been reported.