When Dr. Benjamin Carson and a team of South African doctors set out to separate Siamese twins who were joined at the head, they figured their greatest challenge would be to leave the sisters with fully intact brains.
They were wrong.
Yesterday, in the Johns Hopkins Children's Center, the esteemed neurosurgeon reflected on the surprising difficulties that caused one twin's death hours after surgery and the other's demise a day later.
Dr. Carson, who had traveled to South Africa to assist in the operation two weeks ago, said doctors were ultimately defeated by the fact that the infants were dependent on each other for heart and kidney function -- despite sharing tissue only at the backs of their heads.
"The fact of the matter is that they were symbiotic twins, living off each other," Dr. Carson said. They were so intimately tied, he said, that they would have died even if the operation had been performed in a more sophisticated operating room or if surgery had been passed up.
"If we had done nothing, they would have died within a week or two," he said. "They were rapidly deteriorating."
The girls -- Nthabiseng and Mahlatse Makwaeba -- were born nine months earlier to a couple who lived in a remote region north of Pretoria. During their short lives, the twins looked in opposite directions, unable to crawl or sit up.
Joined at the skull, they shared a large vein that provides the central conduit by which blood leaves the brain. Dividing the vein and rebuilding the halves into two functioning vessels promised to be one of the surgeons' greatest challenges.
That aspect of the 20-hour operation went smoothly, but unforeseen problems proved to be the twins' undoing.
The weaker of the two, Nthabiseng, was born with a heart defect and endured corrective surgery when she was a few months old. Her heart took a turn for the worse as she approached her second operation.
She was in congestive heart failure by the time doctors began the delicate separation. Several hours into surgery, just as doctors were reveling in their success with the brain separation, she went into cardiac arrest.
When doctors opened her chest, they were "aghast" at the heart's appearance, Dr. Carson said.
"It was markedly enlarged, three or four times larger than expected," he said. "Basically, it was just a bag with very little function."
It turned out Mahlatse's heart was doing the work of two.
Nthabiseng's heart was too weak to sustain blood flow on its own. A few hours after the operation, the girl was declared dead.
Meanwhile, Mahlatse seemed on the rebound.
"The next day, she was moving spontaneously," Dr. Carson said. "We were actually optimistic until it became very clear the baby was not putting out any urine" -- a sign her kidneys were not working.
A day later, Mahlatse died of kidney failure. An autopsy showed that the arteries leading into the kidneys were thin and shriveled -- a congenital defect -- allowing very little blood to be filtered.
Surprisingly, Mahlatse had depended on her weaker sister for kidney function.
He said the operation taught him an important lesson: that twins joined at the head may share various organ functions.
Pre-operative tests would have shown that the sisters shared heart and kidney functions. Had they done the tests, he said, they would have known that Nthabiseng was too weak to survive. They would have given her kidneys to her stronger sister in the hope that one could live.
The operation cost less than $100,000, he said.