In a tale like a storyline from a Marvel comic, Italian Sergio Canavero is poised to do the first human head transplant, but others say the charismatic neurosurgeon is peddling false hope.
One autumn day in 1974, 9-year-old Sergio Canavero bought a comic book from his regular newsstand on a bustling street in Turin, Italy.
As a bullied schoolboy, the man who now claims he can complete the first human head transplant was dismally aware of his pitiable social status - "cookie-cutter nerd" - and sought fictional escape.
His attachment to Spider-Man's Peter Parker, another dweeb, lured him deep into the world of Marvel, with its dose of futuristic medicine.
That fateful day, he bought Issue 51 of Marvel Team-Up, in which Dr Strange boasts to Spider-Man and Iron Man, "I myself have surgically rejoined severed neurolinkages. The nerve endings have been fused, the healing process begun."
This marked Canavero's first encounter with the idea of spinal cord fusion. And he wanted more.
Four years ago, the neurosurgeon, now 52, had his own Dr Strange moment when he announced he'd be able to transplant a human head in a procedure he dubs Heaven (head anastomosis venture) and Gemini (the subsequent spinal cord fusion).
The aim is to help patients whose bodies are deteriorating but whose minds are well, by transplanting their heads on to a healthy body.
Last month Canavero's team announced the successful repair of severed spinal cords in rats, confirming their proof-of-principle study and helping show their technique works across the board.
The rats regained movement and no adverse side effects were recorded, according to a study published in the Wiley journal CNS Neuroscience and Therapeutics.
The human operation has been pegged to happen in December.
But many dismiss his plans as fantasy. And if he has a comic book-like nemesis - or maybe a hero? - it is Arthur Caplan, founder of the Division of Bioethics at New York University's School of Medicine.
"I think he's a charlatan, a quack and a self-promoter," says Caplan, who also labels Canavero a "Looney Tune", "peddling false hope".
Those judging Canavero generally assign him to one of two categories: either a Dr Frankenstein seeking fame without regard for risk, or an innovator trying what others consider impossible.
Canavero claims his detractors publicly denounce him but then approach him to learn more.
And in a world of heart, lung, kidney, uterus and hand transplants, he wonders why we can't yet transplant the human head.
In 1970 American neurosurgeon Dr Robert White conducted the first successful transplant of a head to another body when he operated on a rhesus monkey.
Modern spinal cord fusion technology had not yet been developed, and the monkey lived only a few healthy days.
But in 1999, White predicted that what "has always been the stuff of science fiction - the Frankenstein legend - will become a clinical reality early in the 21st century".
Canavero's plan was delineated in a June 2013 paper in the peer-reviewed journal Surgical Neurology International and presented in 2015 as the keynote address of the American Academy of Neurological and Orthopaedic Surgeons' 39th annual conference.
It's a 36-hour, $28 million procedure involving at least 150 people, including doctors, nurses, technicians, psychologists and virtual reality engineers.
Canavero originally announced his patient would be Valery Spiridonov, a Russian who suffers from the degenerative muscular condition Werdnig-Hoffman's disease, but the doctor has since said it is likely to be an as-yet-unnamed Chinese person. The reasons for the change are unclear.
In a special hospital suite, two surgical teams will work simultaneously - one on the patient and the other on the donor's body, a brain-dead patient matched with the patient for height, build and immunotype.
Anaesthetised and outfitted with breathing tubes, both will have their heads locked using metal pins and clamps, and electrodes will be attached to their bodies to monitor brain and heart activity.
Next, the patient's head will be nearly frozen, at 12-15C, rendering him temporarily brain-dead.
Doctors will drain his brain of blood and flush it with a standard surgery solution.
A vascular surgeon will loop sleeve-like tubes made of a silicone-plastic combination around the carotid arteries and jugular veins; these tubes will be tightened to stop blood flow and later loosened to allow circulation when the head and new body are connected.
Then the two teams, working in concert, will make deep incisions around each patient's neck and use colour-coded markings to note all the muscles in the heads of both patient and donor. The most critical step is next.
Under an operating microscope, doctors will cleanly chop through both spinal cords - with a $200,000 diamond nanoblade. Then the rush is on: once sliced, the patient's head will have to be attached to the donor's body and connected to the blood flow within an hour.
Surgeons will quickly sew the arteries and veins of the patient's head to those of his new body. The donor's bloodflow will then, in theory, warm the patient's head to normal temperatures within minutes.
If all goes as planned, Canavero can then make good on his Dr Strange inspiration with Gemini. The lengths of the transected spinal cord stumps will be adjusted so they're even, and the myelinated axons, the spaghetti-like parts of nerve cells, will be fused using a special type of glue made of polyethylene glycol, an inorganic polymer that Canavero says is the procedure's true magical elixir.
In this way, spinal cord function will be established by enabling the cytoplasm of adjacent cells to mix together.
Then it's time to make sure the spinal fusion is secure with a few loose sutures applied around the joined cord and threaded through the thin membrane surrounding the brain and spinal cord.
To finish securing the patient's head, the previously exposed vertebral arteries of the donor and the patient will also be linked to achieve proper blood flow.
In addition, the dura, the tough outermost membrane covering the brain and spinal cord, will be sewn watertight with wires and clamps.
Doctors will similarly reconnect the trachea, esophagus, vagi and phrenic nerves, along with all of the severed muscles, and plastic surgeons will sew the skin for optimal cosmetic results.
The Frankenstein legend will become a clinical reality in the 21st century.
Throughout, doctors will ensure a suppressed immune system through medication, and after the transplant, doctors will screen the patient's blood for anti-donor antibodies while he lies in a drug-induced four-week coma to allow his brain to recover.
During that time, doctors will electrically stimulate the spinal cord to promote communication between neurons and improve the patient's motor and sensory functions. Canavero predicts his patient will be able to walk three to six months after surgery.
Despite the thoroughness of the presentation at the Annapolis, Maryland, conference, Canavero and Spiridonov faced vitriol and doubt.
Spiridonov fielded a question about the ethics of this surgery by asking if anyone would like to be in his shoes: needing assistance with defecation and urination and living a life without sex. A hush fell over the audience.
The Russian said he would rather risk death in this experimental surgery to achieve a higher quality of life than suffer the burdens of his current existence.
"If he is going to die," Canavero said later, "he is the only one who can decide."
Canavero understands. A self-described womaniser who says he studied German-language Spider-Man comics as a bachelor to seduce German-speaking women, he is a hedonist who wants his patients to experience all life's pleasures.
Canavero's collaborator, Xiaoping Ren of Harbin Medical University in China, recently completed a monkey head transplant.
And Canavero's colleague, C-Yoon Kim of the Konkuk University School of Medicine in South Korea, published a study in the journal Spinal Cord showing how his team re-established motor movements in mice whose neck spinal cords had been severed and re-fused.
Dr Michael Sarr, professor emeritus of surgery at the Mayo Clinic and co-editor-in-chief of Surgery, recently accepted one of Canavero's head transplant papers for his publication. "He's a little bit fantastic, but he's a serious guy," Sarr says. "He's not just a showboat.
"This is not science fiction. This is now science. There's experimental work that supports the concept of nerve membrane fusion."
Sarr is particularly interested in how this technique could be applied more widely to treat traumatic spinal cord injury patients. Of course, he admits the surgery has serious risks and wonders how well the patient would function - should he survive.
"Conceptually, much of this could work, but the most favourable outcome will be little more than a Christopher Reeve level of function," says Dr John Adler, a neurosurgeon and professor emeritus at Stanford University's School of Medicine, referring to the Superman actor left paralysed from the neck down after a horse-riding accident.
In other words, the patient might end up with a body that functions not much better than the one he left. Adler says each piece of Canavero's method is viable from a strictly technical sense, but together there's too much risk of failure - paralysis or death for the patient.
The challenges range from whether the axons in the joined section of the spinal cords will form any sort of meaningful connections, to the possibility the patient's brain will suffer irreparable damage during the time it is without blood flow.
Some skeptics are more outspoken. "In my opinion, this procedure has no feasibility at all," says Dr Lorenzo Pinessi, director of the Neurology Clinic at Italy's University of Turin. "It is demented."
The man who volunteered to be a human guinea pig by undertaking the world's first head transplant this year has admitted his dream will never happen.
Severely handicapped Russian Valery Spiridonov, 31, was announced in 2015 as the man to undergo the operation.
But neurosurgeon Sergio Canavero has now announced he will undertake the first such transplant in China with an as-yet-unnamed local patient.
Spiridonov, who worked with Canavero for two years and became the human face of head transplant surgery, acknowledged he had lost his hope of a new body free from disabilities.
He suffers from Werdnig-Hoffman disease, a form of spinal muscular atrophy, and has already defied life expectancy predictions.
"Given that I cannot rely on my Italian colleague, I have to take my health into my own hands," he said.
The Russian will now seek new conventional spinal surgery to improve his life, rather than the transplant that experts warned had a high risk of death. "Luckily, there is quite a well-tested surgery for cases like mine when a steel implant is used to support a spine in a straight position," said Spiridonov.
"There are several places in Russia where they carry out such surgery. It eases breathing and helps [with moving] in public transport, and just [sitting] down.
"The surgery will not bring strong muscles back and won't let me walk, but it will radically improve the quality of my life."
He hopes to use crowdfunding to raise the estimated $57,000 he will need for the operation, a fraction of the vast cost of a head transplant.
- Washington Post, Daily Mail and agencies
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