1-year-old girl has a fetus in her skull that once belonged to her twin sister

A one-year-old girl in China was born with a fetus inside her skull, doctors say in a new case report.

Neurosurgeons operated on the child, who suffered from severe head swelling and developmental delays, but she died within two weeks because the damage to her brain was too severe for survival.

This extremely rare condition, scientifically known as fetus in fetu, affects approximately 1 in 500,000 birthsThere are only 18 known cases where this occurred in the skull.

After the tissue was removed from the brain, the patient never recovered and succumbed to a series of severe seizures. The scans show her brain after the surgery

Doctors don’t yet understand what causes it. But they do know it happens during development in the womb – when identical twins, formed when two eggs split, don’t fully separate.

Then one twin becomes stuck inside the other, and features such as fingernails, hair, and limbs can still develop.

In 80 percent of cases, the absorbed fetal tissue remains in the abdomen, where doctors have a good chance of removing it without harming the patient. Other times, it is found in a child’s mouth, scrotum, or tailbone.

For example, in 2015, Chinese doctors successfully removed a fetus found in the scrotum of a 20-day-old baby.

Bbut the condition is nearly 100 percent fatal if it occurs in the head, Xuewei Qin and Xuanling Chen, study authors and anesthesiologists at Peking University International Hospital in Beijing, China, wrote in the American Journal of Case Reports.

The report states that during a normal check-up in week 33, doctors discovered some “abnormalities” in the skull of the developing embryo.

But her birth was fairly standard — doctors delivered her via C-section at 37 weeks. Her head was larger than average, but she went home with her mother from the hospital.

A year later, she was admitted to Peking University International Hospital because her head was swollen and she was not developing normally.

She was incontinent and had difficulty standing, lifting her head, and pronouncing words other than “mama.”

So her doctors scanned her head, and revealed a 5-inch (13 cm) mass in her skull, slightly larger than a baseball. Embedded in the mass were long pieces of bone.

This scan, taken before the tissue was removed, shows the immature bones that the fetus contained within the child’s skull. The white arrow on the scan points to them

The tissue removed from the skull was about 18 cm long, but when compressed into the skull it was about 13 cm in diameter

At this point, doctors decided to operate to remove the mass. They put the child to sleep and performed a craniotomy, removing part of her skull.

Inside they found a white capsule, containing a thick brown liquid and an immature embryo.

The fetus had a spine and bones, and the first signs of a mouth, eyes, hair, forearms, hands and feet. It was 18 centimeters long.

This caused ‘severe compression of brain tissue’. The patient never woke up and was kept on a ventilator while being shaken by seizures after the operation.

Twelve days after the operation, the family decided to take her off the ventilator.

The cause of these malformations remains a mystery, the study authors write. They could be linked to environmental pollution, genetics, cold temperatures, pesticide exposure during pregnancy or problems with egg division.