A rare medical condition, which has only been recorded a handful of times, has seen doctors surgically remove the foetus of a twin from the skull of its one-year-old sister.
The foetus, which has grown upper arms, bones and even fingernails, is about four inches long, and was only discovered when the parents took their daughter for a check-up at the hospital because she had an enlarged head and problems with motor skills.
Foetus-in-foetu is the term used to describe the rare event when twins are joined together in the womb, of which there are only 200 recorded of which 18 occurred inside the skull.
It is thought to be caused by incomplete separation when a single egg splits or as late cell division.
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Despite surviving a year after birth thanks to its shared blood supply, it’s unclear if the surviving twin will suffer long-term damage.
Dr. Zongze Li from Huashan Hospital, Fudan University who treated the girl said that “the intracranial foetus-in-foetu is proposed to arise from unseparated blastocysts.”
There are further similar cases in medical literature; in 2017 Thailand discovered three siblings inside the skull of an unborn girl connected by a single artery and vein; likewise in 2015, China found an unborn foetus inside its male twin’s scrotal sac.
All were successfully removed via surgery with full recovery for their twins.
