A hospital in Rome said on Tuesday it had successfully separated two-year-old twins joined above the nape of their necks, after three risky surgeries.

Joined skull to skull, sisters Ervina and Prefina were born with a condition the Bambino Gesu (Baby Jesus) Pediatric Hospital in Rome called "one of the rarest and most complex forms of cranial and cerebral fusion." 

The hospital said it was the first time in Italy and likely the world -- as such a case had never been cited in medical literature -- that surgeons were able to separate twins joined in such a way, sharing the back of their skull and its venous system.

The two sisters from Bangui, Central African Republic, were brought to Italy in September 2018 after the hospital's president met the twins and their mother at a medical centre where they were born.

Tests conducted in Italy showed the twins to be generally in good health but that one sister's heart was working harder to maintain the "physiological balance of the organs of both, including the brain." 

The girls had "distinct" personalities, the hospital said, Prefina being vivacious and playful with her sister Ervina more serious and quietly observing.

The greatest challenge facing the team of specialists -- including neurosurgeons, anaesthesiologists, neuroradiologists, plastic surgeons, engineers, and physiotherapists -- was the shared network of blood vessels bringing blood from the girls' brains to their hearts, the hospital said in a statement. 

That required "three very delicate operations to progressively reconstruct two independent venous systems," it said. 

'Lead a normal life' 

The final surgery, which took 18 hours and involved 30 doctors and nurses, took place on June 5 when the bones of the shared skull were divided.

Surgeons then reconstructed the membrane covering the two brains and recreated the skin lining over the new skulls. 

"A month after the final separation, the twins are fine," said the hospital. 

Video images of a hospital party given for the twins' second birthday with their mother on June 29 showed the girls, their heads wrapped in protective bandages, gesticulating and grabbing at their birthday cake. 

The hospital cautioned that the risk of infection was still present and the girls would have to wear protective helmets for a few months. 

But post-operative controls showed that their brains were "intact," adding that they will have the opportunity to grow normally and "lead a normal life, like all girls of their age." 

It was the fourth time the hospital had operated on conjoined twins in its history.

Twins conjoined by the skull are extremely rare, or approximately one case every 2.5 million live births, the hospital said, adding that in Europe in the past 20 years only two cases of separating twins joined at the top of their skulls had been successful.