Doctors in Singapore have begun unprecedented surgery to separate 29-year-old Iranian twin sisters who have been joined at the head since birth.
The Bijanis long to see each other's faces
Ladan and Laleh Bijani have been told that they have a 50-50 chance of survival but say they are willing to risk death for the chance to lead separate lives.
The operation - at the Raffles hospital - involves an international team of 28 doctors and 100 medical assistants and is expected to last for 48 hours.
The sisters will be sitting down throughout the surgery.
The operation marks the first time surgeons have tried to separate adult craniopagus twins - siblings born joined at the head - since the operation was first successfully performed in 1952.
"We've never been as confident as we are now," Ladan said before the operation
"We are prepared by all means to embrace the risks and walk into the operation room."
German doctors had turned away the Bijanis in 1996, deeming the operation too risky.
The 128-strong medical team will attempt to repeat the success of the first triumphant operation in 1952
The petite Iranian sisters, who have separately functioning brains encased in one skull said they know about the risks but are keen on the operation which they have wanted for years.
They arrived in Singapore last November for medical and psychological tests after hearing the success story of a separation of a pair of 11-month-old Nepali twins who had a similar brain structure.
Chief surgeon at Raffles, Dr Keith Goh - who was responsible for that separation and will operate on the Bijanis - said he had to weigh up quality of life against risk before he could proceed.
Their present quality of life is so poor that this huge, this immense surgery is justified
Dr Keith Goh, Raffles Hospital - Singapore
"We have to be convinced that the present quality of life is so poor that this huge, this immense surgery is justified and should be performed.
"So, over the last few months seeing them almost everyday, observing reactions of people around them, strangers, children, adults, I think quality of life is a serious issue which warrants the undertaking of this surgical procedure," he said.
Doctors have conducted five hours of last-minute tests on the sisters to study how blood flows through their brains.
The surgeons' biggest challenge will be dealing with a shared vein that drains blood from their brains.
Vascular surgeons will take a large vein from one sister's thigh to be used as graft for the bypass to replace the shared vein and re-route blood flow within both brains.
The next stage will be the separation of the brains before the final surgical process of reconstruction of the skin and soft tissue on the exposed area of their heads, using muscle and skin grafts.
Surgical complications can include formation of blood clots in the newly constructed blood vessels, intracranial bleeding, heart complications and infection.
The sisters will continue to undergo psychological counselling after surgery to manage the emotional effects of separation.
The Bijani sisters were born in Firouzabad, southern Iran in 1974.
They have wanted to be separated ever since they first opened their eyes, Ladan told a news conference last month.
They told reporters they long for simple things such as seeing each other's face.
Both sisters studied law because Ladan wanted to be a lawyer.
But after the surgery, Laleh wants to move to Tehran to be a journalist, while Ladan wants to move back home with her parents and continue her studies to qualify as a lawyer.