An unborn fetus has been surgically removed from the skull of its one-year-old twin sister — in a medical anomaly that has only been recorded a few times.
Doctors said the fetus had developed upper limbs, bones and even fingernails, meaning it likely continued to grow for months while it was in its sibling’s womb.
The unborn child – who was about four inches long – was not discovered until the parents took their daughter for hospital scans because she had an enlarged head and motor problems.
Fetus-in-fetu is the medical term for the rare phenomenon where twins fuse in the womb and one physically develops inside the other.
Only about 200 cases have ever been documented, of which only 18 occurred in the skull.
The above shows a scan of the baby girl’s skull with the unborn fetus depicted inside. The scan above shows the presence of bones
Doctors said the fetus had developed upper limbs, bones and even fingernails, meaning it likely continued to grow for months while it was in its sibling’s womb.
Fetus-in-fetu has also been detected in the pelvis, mouth, intestines and even the scrotum.
The condition is caused by the incomplete separation of identical twins, which form when an egg splits. However, doctors are not exactly sure how this happens.
Some have theorized that the healthy connects to the mother through the placenta, while the other attaches to the twin’s blood vessels.
As the larger twin grows, the smaller one is absorbed into their abdomen. Other scientists have suggested that it happens due to late cell division.
The above image shows the unborn 4-inch fetus after it was removed from its sibling’s skull in China
The nonviable fetus can continue to develop inside its sibling for several weeks and months — even forming organs, bones, and limbs.
The latest story was revealed in December in the journal of the American Academy of Neurology Neurology.
The unnamed girl was taken to hospital after showing problems with her motor skills.
Doctors have not given further details, but this could include problems walking or sitting.
CT scans revealed that her unborn sibling was pressed against her brain.
She also had hydrocephalus, the accumulation of fluid deep in the brain, which can cause an enlarged head, extreme drowsiness and seizures.
Doctors said it had survived a year after birth because it shared a blood supply with its sibling.
It was unclear whether the surviving twin will sustain long-term harm.
Dr. Zongze Li, a neurologist at Huashan Hospial, Fudan University who treated the girl, said: ‘The intracranial fetus-in-fetu would arise from unseparated blastocysts.
“The joined parts develop into the forebrain of the recipient fetus and envelop the other embryo during the folding of the neural plate.”
The case is one of only 18 reported in the medical literature to date.
Doctors in Thailand 2017, found three siblings in the skull of an unborn girl.
They said they all had “several well-developed organs,” including a nervous, digestive and respiratory system.
They were connected to the host sibling through a single artery and vein, which the doctors said was the umbilical cord.
In another case from 2015Also in China, doctors found an unborn fetus in the scrotal sac of his male twin.
The 20-day-old baby was taken to hospital after birth when his scrotum began to swell.
Scans revealed a “well-defined … mass” in the scrotum, complete with bones and knobs that doctors said would have formed into limbs.
The unborn fetus was removed via surgery and the twin brother was discharged five days after surgery after making a full recovery.