Dr. Jorge Lazareff, director of the UCLA Pediatric Neurosurgery Program and lead neurosurgeon, smiles at a news conference, Tuesday, Aug. 6, 2002

Maria Teresa Quiej Alvarez and her sister, Maria de Jesus, were in critical but stable condition Tuesday night at the University of California at Los Angeles Medical Center, but doctors were optimistic about their recovery. They were expected to remain sedated¹ and using breathing tubes for days.

"I'm absolutely positive they will do OK. I'm absolutely positive if you go and visit them in five years they will be leading a normal life," said Dr. Jorge Lazareff, the lead neurosurgeon.

The doctors' sense was that the girls fared well, but it remained to be determined² whether they suffered any brain damage, said Dr. John Frazee, another neurosurgeon.

"They're moving, which is a good sign. There's no way of knowing what the state of affairs is for another week," Frazee said.

After the 22-hour risky³ separation surgery, Maria Teresa was wheeled back into the operating room for nearly five more hours because of a buildup of blood on her brain, Lazareff said.

The girls were born attached at the top of the skull⁴ and faced opposite directions. While the two shared bone and blood vessels⁵, they had separate brains. Cases like theirs occur in fewer than one in 2.5 million live births.

In the riskiest⁶ part of the surgery, doctors had to separate blood vessels the two girls shared and decide which belonged to each child. That was followed by plastic surgery to extend each girl's scalp to cover the area where they had been attached.

The two face still more operations to reconstruct their skulls⁷.

Surgeons around the world have performed cranial separations only five other times in the past decade, and not all twins have survived.