How a 'parasitic unborn twin' was found in a one-year-old girl's brain in China

Doctors in China have found an “unborn twin” in the brain of a one-year-old child in Shanghai.

It could sound like a scene from the 2021 film Malignant – in which the living twin is controlled by a parasitic twin who lives within her skull.

But this case is hardly sci-fi.

The study published in the scientific journal Neurology in December revealed that the girl was brought in after she was having difficulty with her motor functions.

She was not growing at the typical rate for a child her age, and her skull was enlarged.

When doctors took an X-ray of her skull, they were amazed to find bones in a sac inside her brain.

They said the extremely rare phenomenon was an intraventricular fetus-in-fetu.

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What is fetus-in-fetu?

Fetus-in-fetu (FIF), sometimes called a parasitic twin, occurs when a malformed foetus is enclosed within the body of its twin, reported Dailymail.

UK-based website IIFL science explained that such cases are thought to occur during the very early stages of twin pregnancy when the cluster of dividing cells made by a fertilized egg, called the blastocyst, fail to separate properly.

One of the early embryos ends up being encircled by the other as a result. It cannot develop since it is surrounded by the other twin’s cells that are actively dividing, but it is kept “alive” by the twin’s blood supply.

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These are incredibly rare cases.

If the most reliable figures are to be believed such cases occur in around one in every 500,000 births and can affect both males and females.

Less than 200 incidences of the highly unusual condition have been reported in medical literature, according to Dailymail. Only 18 cases in which the foetus has been discovered inside the sibling’s skull are known.

Although it is often found in infants, there have been a few reports of occurrences in adults as well.

Symptoms include a visible abdominal mass. The presence of a FIF must be verified using scans.

One to three FIFs is typically present. But, eight foetuses were discovered in one case in India’s Jharkhand in October 2022.

The foetus can then be surgically removed by doctors. Patients typically fully recover.

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The tough surgery

For the health of the one-year-old, doctors determined that the parasitic twin needed to be removed.

The foetus they removed was a 10-centimetre-long and was developing arms and hands. Although it had a spine, it was still quite underdeveloped, according to Miami Herald.

It was described by the doctors as a “fetiform,” a growth that resembled a foetus. Genetic testing on the growth revealed that it was the twin of the living girl who had been absorbed during a developmental process called neural plate folding – a step necessary for the structure of the brain and spinal cord.

This would clarify how the parasitic foetus found its way inside the skull of its sister.

Similar cases

There have been other instances where the baby has made a full recovery.

Scientists at the London Hospital reported a 14-centimetre (5.5-inch) long foetus in a 6-week-old infant who presented with an expanding head size in a research that was published in 1982, according to IIFL Science.

Additionally, the removed foetus exhibited distinguishable characteristics including growing limbs, a head, and a body. The young patient had a “great recovery” following surgery, according to reports.

With inputs from agencies

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