The surgeons have removed the growth from Sam Esquibel's head, and the three-month-old boy is now said to be fit and healthy.

The baby’s mother, Tiffnie Esquibel, has described his survival as a "miracle".

The ultrasound tests on Sam's heavily pregnant mum showed that the unborn child had a tumour in his brain, but it actually turned out to be a tiny foot during the surgery.

The brain also had other partially formed body parts including a second foot, a hand and a thigh.

The doctors believe that the condition was probably a teratoma, a type of tumour that contains hair, teeth, bones and body organs, but usually does not occur in the brain.

Another theory is that Sam suffered from a condition called fetus in fetu, in which one twin envelops the other, but the disorder is so rare that there have been fewer than 100 reported incidents in the world.

"When I went into hospital I thought, OK we're going to come out of here with a baby in our arms," the Telegraph quoted Tiffnie as saying.

"But we didn't – he was in another hospital. They told us it was a 50-50 chance whether he could make it through it or not," she added.