Sisters conjoined at the head are separated after 50 hours of surgery

Conjoined twins Safa and Marwa are recovering well after complex surgery at London's Great Ormond Street Hospital.

London (CNN)A pair of Pakistani conjoined twins are finally living independent lives after a 100-strong team of British medical experts spent 50 hours performing complex surgery to separate them.

Safa and Marwa Ullah came as a bit of a surprise when they were born in January 2017 as their mother had not known she was expecting twins -- let alone craniopagus twins, who are joined at the head.
Around two in five sets of craniopagus twins are stillborn or die during labor, while a third more do not survive the first 24 hours. Fortunately in the sisters' case, a wealthy benefactor offered to cover the costs of their long journey from home in Charsadda, Pakistan, for the surgery at London's Great Ormond Street Hospital (GOSH).
    According to its website, GOSH "is one of only a few hospitals in the world to have the infrastructure, facilities and team of experts" to separate conjoined twins. It has carried out the procedure more times than any other hospital worldwide.
    Born by cesarean section, the girls emerged with their skulls and blood vessels fused together. Since arriving in Britain, they have undergone three operations between October of last year and when they were finally separated on February 11.
    Such a procedure is extraordinarily rare; according to GOSH, the chances of craniopagus twins undergoing surgery is around one in 10 million. Around 5% of conjoined twins are craniopagus cases.
    After consultation with their doctors in Pakistan, the London hospital welcomed them to the Bumblebee Ward where various experts -- from craniofacial, neurology and psychology specialists, to nurses, radiologists and physiotherapists -- spent four months treating them.
    Safa and Marwa before they were separated.
    Consultant neurosurgeon Noor ul Owase Jeelani and craniofacial surgeon Professor David Dunaway led a team of 100 staff members.
    Now, five months after the last operation, the hospital has told the twins' tale. A short animation video released by GOSH explains the procedure, while separate footage sees the medical team recount their efforts.
    Jeelani explained that conjoined twins are "very, very unusual," but even more so those joined at the head.
    The secret of the "very complex procedures," according to Jeelani, was breaking it down to smaller and "much more manageable steps."
    The experts used virtual reality to create an exact replica of the girls' anatomy in order to visualize their skulls and the positioning of their brains and blood vessels.
    "For the first two to three procedures we focused on separating out the brains and blood vessels," Jeelani said in the GOSH video.
    Once this was completed, a piece of plastic was used to keep the two structures apart. "Internally we had two separate kids," the neurosurgeon added.
    The focus was then external, as the team used the girls' own bone at the top of their skulls and "tissue expanders" to stretch their skin over their heads.