Rare surgery: Unborn twin removed from brain of 1-year-old in China

Cases are exceptionally rare and occur in one in every 500,000 births

Such incidents have been reported in medical literature but are highly uncommon.

Fetus-in-fetu cases usually occur during the very early stages of twin pregnancy when the blastocyst, which is a cluster of dividing cells made by a fertilized egg, fails to separate properly. It results in one of the embryos being enveloped by the other. However, it is to be noted that the encased embryo does not die. Thanks to regular blood supply from the other twin, it remains "alive" but fails to develop.

"The conjoined parts develop into the forebrain of the host fetus and envelop the other embryo during neural plate folding," the researchers add.

There is no mention of the one-year-old's recovery, as the case report is brief. Though a tough operation, previous cases have recorded full recovery. In one such study published in 1982, scientists at the London Hospital reported a 5.5-inch (14-centimeter) long fetus in a six-week-old child who had an enlarged head.

The encased fetus had developing limbs, a head, and a body. Post-surgery, the developed twin had an "excellent recovery".

How rare are these cases? One in every 500,000 births, reports say. They are mostly found within the bodies of live babies, making it uncommon to affect the brain.

The case study was reported in the open-access journal Neurology. 

Study Abstract:

An intraventricular fetus-in-fetu, a malformed monochorionic diamniotic twin, was identified in a 1-year-old girl with motor delay and enlarged head circumference. After surgical removal, whole-genome sequencing revealed identical single-nucleotide variants in the host child and fetus-in-fetu, with extensive de novo copy number gains in the fetus-in-fetu, suggesting the significance of copy number variation during embryogenesis.