A ONE-year-old girl with a fast swelling head passed away just days after doctors discovered a foetus that was once her twin sister growing in her skull.
The toddler was admitted to hospital due to her growing skull and inability to sit up or stand.
She also had delays in motor skills and speech development, only able to say “mum”.
After scans revealed that the baby girl's symptoms were cause by a feotus - which had a spine, organs and fingers - growing in her brain, neurosurgeons removed the embryo from her skull.
But the one-year-old passed away just 12 days after the surgery, as the damage to her brain was too severe.
Her incredibly rare condition is known as fetus in fetu (FIF), or parasitic fetus, occurring in about one in 500,000 births.
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It's a rare developmental abnormality in which a malformed fetus is found within the body of the other twin - usually in the abdomen.
But foetuses have also been found in other unusual locations, such as the skull, pelvis and mouth.
Less than 200 cases have been reported in medical literature.
The condition is nearly 100 percent fatal when it occurs in the head, Xuewei Qin and Xuanling Chen, study authors and anesthesiologists from Peking University International Hospital in Beijing, China, wrote in the.
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"FIFs remain a mystery, and their causes and mechanisms may be related to environmental pollution, genetics, low temperatures, pesticide exposure during early pregnancy, and other factors," they said in their report of the girl's case.
The condition tends to only be spotted in the later stages of pregnancy, making early diagnosis challenging.
In the one-year-old's case, doctors detected abnormalities in her head when her mum was 33 weeks pregnant, during a prenatal examination.
But the MRI couldn't provide any further information.
The little girl was delivered via cesarean 37 weeks, as she was in breech position - meaning she was lying feet first in the womb instead of the usual head first position.
Even then, doctors noted that her head was abnormally large.
"Upon birth, the infant’s head circumference was larger than that of a child of the same age," case report authors said.
When she was admitted to hospital at a year old, she couldn't sit up or walk and "could only raise her head slightly".
The only word the one-year-old could say was "mum".
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She was also incontinent and had poor motor skills in her hands.
Though her height was about 70cm, her head circumference was 56.6cm.
Doctors performed a CT scan on her skull, which revealed "soft tissue, limb-like bone, and mixed bone tissue shadows in the intracranial area".
It was decided the girl would undergo a craniotomy.
Surgoens discovered a "white capsule" in her brain tissue - upon opening it, they saw "a finger-like limb protruding from its opening".
"We removed an immature embryo, with visible vernix and organs, such as the mouth, eyes, fetal head, fetal hair, body, forearm, hands, and feet," the case report authors wrote.
The embryo was 18cm long - it had malformed features and limbs, as well as long bones and a spine.
Sadly, the little girl remained unconscious after her surgery and suffered seizures.
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She died 12 days after the procedure.
Doctors made a shock discovery when treating a baby girl for stomach pain last year - left stunned to find she had her unborn twin inside her tummy.