] Neurosurgeons separating 29-year-old Iranian sisters ] joined at the head cut through brain tissue millimeter by ] millimeter Tuesday after rerouting a thick, shared vein ] and stitching in a new one. ] ] The team of doctors also contended with unstable pressure ] levels inside the twins' fused skulls as they began ] uncoupling the sisters' brains, a hospital official said. ] The risky, marathon procedure which could kill both women ] began about 10 p.m. EDT Saturday and could take four ] days. |