Before him lay Siamese twins, their brains joined by an elaborate network of blood vessels. The myriad folds and planes came into view.
He saw where the brains divided. He studied the features from every conceivable angle. He memorized the terrain. He planned his moves.
This was Dr. Benjamin Carson's rehearsal -- done in the eerie space of virtual reality.
Today, the Johns Hopkins neurosurgeon is celebrating that two 11-month-old boys are recovering splendidly -- and separately -- in the South African hospital where he and more than 20 doctors and nurses performed an exhausting operation that lasted more than a day.
"We expect them to be perfectly normal, which is pretty mind-boggling," said Carson, who tried a decade ago to separate joined-at-the-head twins with less happy results.
The operation, done in the waning hours of 1997, has been front-page news in South Africa, drawing attention similar to America's reaction to the Iowa septuplets.
The successful outcome, Carson said, was enhanced by his dry run on a three-dimensional likeness made possible by computers, goggles and a projection machine.
It's the same technology that makes video-game aficionados drool with anticipation, but its most exciting possibilities are being realized in the increasingly high-tech world of surgery.
At Hopkins, surgeons are using three-dimensional imagery to plot out such delicate procedures as brain, spine and sinus surgery.
Perhaps at no time has its potential been realized as dramatically as in the case of Luka and Joseph Banda, Zambian twins who were taken to Pretoria's Ga-Rankuwa hospital in October and separated Dec. 31 in a procedure that took 28 hours.
Just days before Carson flew to South Africa, he practiced before a three-dimensional projection in Baltimore.
Holding mock instruments, he peeled away layers of brain tissue, probing deeper and deeper into the territory that he would face in real life.
"You can actually get all the surface topography in mind," said Carson, who, at 45, is well known for his skills as a pediatric neurosurgeon.
"We actually practiced the operation before doing it, which is sort of a way of cheating."
By the time he probed the boys' skulls in person, he felt as if he had been there before.
All signs are promising
"There have been about 23 attempts to separate such twins in the past," Carson said.
"As far as we now, this is the first time anybody's been able to completely separate them in one operation -- not only with both surviving but apparently with no deficits."
Dr. Sam Mokgokong, the South African surgeon who sought out Carson, said the boys show every sign that they are functioning normally.
"As of today, they are feeding orally, crying when hungry and kicking about," said Mokgokong. "They are eating soft porridge.
"They are recognizing familiar things like their mother's voice. We are very happy with the progress."
Mokgokong said it is too early to say with certainty that they will never show any ill effects from the surgery.
The outlook will become clearer when the boys are old enough to talk and perform other higher-level skills.
Their mother, Joyce Banda, who has five children, went to South Africa because Zambia did not have the facilities to perform the operation.
It was the second time Mokgokong called upon Carson to help separate conjoined twins at the Pretoria hospital.
The earlier set of twins, in 1994, died within hours of surgery because they were completely "symbiotic," sharing heart and kidney functions.
Carson and Mokgokong had each tried to separate twins joined at the head.
Mokgokong's patients died; Carson's patients, Patrick and Benjamin Binder of Germany, survived with severe neurological deficits that left them institutionalized.
The African twins were joined at the tops of their brains, facing in opposite directions.
Carson said their skull was like one continuous tube, lacking any horizontal separation between one brain and the other. Inside the skull, the brains touched but shared no gray matter.
What they shared, however, were dozens of blood vessels that made the separation much more than a matter of cutting the skull and pulling the boys apart.
In effect, blood flowed in veins from Luka's brain into Joseph's, and from Joseph's into Luka's.
Surgeons faced the daunting task of severing each vein and then establishing a new connection so that blood could find a new place to drain.
"For every vessel you severed, you had to decide which boy to give it to," Carson said.
And this is where virtual reality was, quite possibly, a life saver.
Before Carson could make his practice run, doctors in South Africa took a series of magnetic-resonance images (MRI) of the boys' skulls.
These images are flat pictures, each giving a different cross section of brain.
The Pretoria hospital sent the images on disc to Hopkins, where another computer assembled hundreds of these slices into a three-dimensional whole.