SUDANESE TWINS BORN with the tops of their heads joined together have been separated in a rare and risky series of operations at a London children’s hospital, officials said.

Facing the World, a charity which helps disfigured children, said it had helped fund the four-stage operation on 11-month-olds Rital and Ritag Gaboura. Twins born joined at the head are known as craniopagus twins and they occur in about one in 2.5 million births.

Separating them can be dangerous, especially if — as in this case — there’s significant blood flow between their brains.

“Incidences of surviving twins with this condition is extremely rare,” lead surgeon David Dunaway said in a statement released by the charity. “The task presented innumerable challenges and we were all very aware of our responsibilities to the family and these two little girls.”

The charity released before and after photographs of the girls. The before photo showed the two sprawled out on a bed, with their heads joined just above the hairline to form what appeared to be a single, solid unit. Facing the World said that separation took place in stages at London’s Great Ormond Street Hospital, with two operations in May, the insertion of tissue expanders in July and the final separation on 15 August.

“Within days the twins were back on the general ward interacting and playing as before,” the charity said. Its executive coordinator, Sarah Driver-Jowitt, predicted that the girls’ parents — who haven’t been named — may soon return home “with two healthy, separate girls.”

Although rare, operations to separate twins linked by their heads aren’t unheard of. In 2004, a team of doctors at New York’s Montefiore Children’s Hospital separated Filipino twins in four major surgeries that took place over 10 months. In 2003, surgeons in Dallas successfully separated 2-year-old Egyptian twins joined at the head.

One of the first successful operations to separate craniopagus twins took place in 1956, according to the US National Library of Medicine.