[xxxnowayxxx]

As it was mentioned before, the parasite one has anencephaly ( means he/she a bigger or smaller part of his/her brain and skull, in most cases brain is visible, this deformity is fatal, the oldest survivor died at age of 3. ) The "normal" twin could be a goner too, if they share any organs and will be damaged during the surgery. There is an other option too, which is a lot more uncomfortable, which is leaving the parasite there (there is a picture somewhere that it actually "works").