A WOMAN being treated at the Cleveland Clinic in Ohio has an almost entirely new face following the most extensive facial transplant yet performed.

The surgery is the first face transplant in the US and the fourth in the world. Few details about the patient had been released in advance of a news briefing scheduled for yesterday.

About 80 per cent of the patient's face has been replaced with skin and muscles harvested from a cadaver. The patient's family has asked that her name and age not be released so that she may remain anonymous, the clinic said.

Dr Maria Siemionow, the Cleveland Clinic plastic surgeon who performed the marathon procedure, is well known among microsurgery specialists, and colleagues were quick to praise the achievement. "We're on the threshold of a whole new way of correcting defects," said Dr Warren C Breidenbach of the University of Louisville, who performed the first hand transplant in the US.

Dr Siemionow and her colleagues spent years preparing for the surgery, practising on animals and cadavers, according to Dr James Bradley, a professor of plastic surgery at the University of California, Los Angeles, medical centre.

Isabelle Dinoire (41), a mother of two in France, became the first recipient of a partial face transplant in 2005 after the lower part of her face was mauled by her pet Labrador. Two other people have received face transplants since - a man in France who suffered from a genetic condition and a man in China who was attacked by a bear.

The surgery in Cleveland probably lasted between six and 10 hours as surgeons grafted the blood vessels, muscles and skin from the donor on to the patient, Dr Bradley said. It could take months before the nerves have healed enough to gauge the success of the procedure, he added.

After the swelling subsides, the patient will not look exactly like the woman who donated her face.

"You look more like a cousin," Dr Bradley said. "The bone structure is your own, but the skin is from another person."

Transplanting a face is not any more of a technical feat than transplanting a hand, surgeons said. But a face transplant has a unique set of complications. "You have to wait for a donor, and that's not easy," Dr Breidenbach said. "A lot of donor families are in shock and grief because their loved one died and they have to donate a very visible part of the person."

Finding the right patient is even more difficult. The patient's psychological state is especially important because his or her recovery depends on a willingness to adopt a healthy lifestyle that will minimise the risk of infection.Compared to internal organs, the risk of rejection with a transplant involving skin is especially high, Dr Bradley said.