Dallas ? A team of 18 doctors began a complicated separation surgery Saturday in an attempt to give 2-year-old conjoined twins from Egypt a chance at independent lives.

The risks are high: One or both of the boys may die, and even if they survive, some brain damage is possible.

“Ahmed and Mohamed Ibrahim have begun the first stage of their surgery that will physically separate them and — we all hope — will give them the opportunity to grow and develop like other brothers,” said Dr. Jim Thomas, chief of critical care medicine at Children’s Medical Center Dallas.

By mid-afternoon, doctors entered a critical stage as neurosurgeons prepared to separate an intricate web of shared blood vessels, Thomas said.

Thomas relayed a message from Dr. Dale Swift, one of five pediatric neurosurgeons: “Everything is going fine. There have been no problems.”

Saturday evening, the hospital said the surgery was continuing and the twins’ condition was stable.

Doctors spent more than a year planning the surgery to separate the boys joined at the crown of the head. The operation was expected to take a team of 50 to 60 medical personnel anywhere from 18 to 90 hours to finish.

Relatives of the boys in the tiny village of el-Homr, near the southern Egyptian city of Qus, prayed for their safe return.

“It is all in God’s hands now,” an uncle of the twins, Nasser Mohammed Ibrahim, said in a telephone interview. “He is the one who can save their lives.”

Thomas said much of Saturday morning was spent positioning the boys in a specially made bed that lets doctors swivel their bodies for easy access to the front and back of their heads.

Craniofacial surgeons planned to open the boys’ scalp and remove skin expanders inserted about five months ago. The extra skin and tissue created by the expanders will cover the head wounds.

While each boy has his own brain, they share an extensive attachment of blood vessels, which neurosurgeons must separate.