A baby girl has been born with two mouths due to a condition so rare that it has only been seen in 35 recorded cases since 1900.
Doctors were initially baffled when the abnormality was picked up on a scan during the mother's third trimester.
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Their initial range of possible diagnoses included a cyst, a bone disorder or teratoma, which is when a twin absorbs another during development in the womb.
But when the infant was born in Charleston, South Carolina, doctors found what they described as a "duplicated oral cavity", or second mouth.
This included another lip, set of six teeth and even a small tongue that moved at the same time as the tongue in her main mouth.
Although the condition was seemingly harmless, they performed an operation to remove the additional feature.
Six months later, the baby was almost completely unaffected by the ordeal, only suffering some swelling and a minor nerve defect in her bottom lip.
No further treatment was needed, according to the study published in BMJ Case Reports.
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The authors said: "Our patient's craniofacial duplication is a rare case that presented as an isolated anomaly, with no associated syndromes or abnormalities.
"At six-month follow-up, the incisions were well healed and the patient was feeding without difficulty."
They explained the condition known as diprosopus, the duplication of facial features, was "extremely rare" - with only 35 cases reported in medical literature in the last 120 years.
Also known as craniofacial duplication, it has been detected in animals including chickens, cats, goats and pigs.
Previous cases involving humans include twins born in Sydney, Australia, in 2014 with one body and one head but two identical faces.
Called Hope and Faith, they died 19 days after their birth.
And in 2008, Lali Singh was born in a village near Delhi, India, in what it is claimed is the only case of a living individual with complete facial duplication.
Doctors involved in her treatment reported she had two pairs of eyes, two noses and two mouths but only one pair of ears.
Seen by some as the reincarnation of the Hindu goddess Durga, who is sometimes depicted with many limbs and eyes, she died due to complications two months after being born.