Surgeons spent months trialling techniques using virtual reality before beginning the real procedures on the three-year-old Brazilian boys.
Conjoined twins who shared fused brains have been successfully separated after 33 hours of operations.
Bernardo and Arthur Lima underwent several surgeries in Rio de Janeiro, under the direction of UK-based paediatric surgeon Noor ul Owase Jeelani from London’s Great Ormond Street Hospital.
The three-year-old boys had a total of seven operations, involving more than 33 hours of operating time in the final two surgeries alone, and 100 medical staff were involved.
Surgeons spent months trialling techniques using virtual reality before beginning the real procedures.
Their surgery was led by Mr Jeelani, alongside Dr Gabriel Mufarrej, head of paediatric surgery at Instituto Estadual do Cerebro Paulo Niemeyer.
Mr Jeelani described the operation as a “remarkable achievement” by medics, but added the charity, Gemini Untwined, relies on public donations to keep its work going.
He said: “The successful separation of Bernardo and Arthur is a remarkable achievement by the team in Rio and a fantastic example of why the work of Gemini Untwined is so valuable.
“Not only have we provided a new future for the boys and their family, we have equipped the local team with the capabilities and confidence to undertake such complex work successfully again in the future.
“It is through this process of teamwork and knowledge-sharing globally that we can hope to improve the outcome for all children and families that find themselves in this difficult position.
“This is only possible through generous donations from members of the public.”
Gabriel Mufarrej said the hospital where he works had been caring for the boys for two and a half years, and their surgery will be “life-changing”.
He said: “Since the parents of the boys came from their home in the Roraima region to Rio to seek our help two and a half years ago, they had become part of our family here in the hospital.
“We are delighted that the surgery went so well and the boys and their family have had such a life-changing outcome.”
Their work was supported by Gemini Untwined, a charity founded by Mr Jaleeni to raise funds for siblings born joined at the head – called craniopagus twins.
Freeing Bernardo and Arthur from one another was one of the most complex separation processes ever completed, and many surgeons did not think it would be possible, according to the charity.
Since the twins are almost four years old, they are also the oldest craniopagus twins with a fused brain to have been separated.
Both twins are recovering well in hospital, and will be supported with six months of rehabilitation, the charity has said.
According to Gemini figures, one in 60,000 births result in conjoined twins, and only 5% of these are craniopagus children.