That is awful :( I've seen this picture before....
I think this was the results of a case of TTTS: Twin to Twin Transfusion Syndrome.
What happens is that when identical twins are in the womb together, one twin starts to receive più blood and oxygen then the other twin. Usually, this twin receives it actually from the other twin.
So with receiving almost everything both twins need, this twin becomes clearly larger then the twin who is getting less of the nutrients.
Both babies' lives are in danger, because one twin is getting far too much of what he o she needs, while the other twin is getting too less. There have been cases where one o both bambini die, so these little boys lucked out. :)