Ook in Wired: van Ladan en Ladeh Bijani:

The surgeons in the operating room, however, felt only dread. They abandoned the back of the brains and set to work separating from the front, as far away as possible from the unforeseen vein. The bypass continued to work, but only sluggishly. It was clear that the second pathway was draining more than half of the blood from the twins’ heads.