Dr. Paul Grabb, a pediatric brain surgeon, said he was surprised when he discovered a small foot growing inside the brain of 3-day-old Sam Esquibel.

When Grabb performed the life-saving surgery at Memorial Hospital for Children in Colorado Springs, he was in for another surprise: he also found what appeared to be parts of an intestine in the folds of the infant's tiny brain, in addition to another developing foot, hand and thigh.

The reason for the strange growth was not clear at first. It was thought to be a teratoma -- a congenital brain tumor composed of foreign tissue such as muscle, hair or teeth -- or a fetus in fetu, which is a developmental abnormality in which a fetal twin begins to form within the other.

"You show those pictures to the most experienced pediatric neurosurgeons in the world, and they've never seen anything like it," Grabb said. "This is completely abnormal."