Separating sisters: inside the groundbreaking surgery

On July 25, 2001, in a small Guatemalan village, Alba Leticia Alvarez gave birth to identical twin girls. The sisters shared nearly everything: beautiful brown eyes, angelic smiles, even the same first name, Maria. But they also shared an extraordinarily rare birth defect. Maria Teresa and Maria de Jesus were born attached at the top of the head--their faces fixed outward, turned in opposite directions. A web of blood vessels sprawled between their conjoined skulls, bridging their circulatory systems (heart, blood, arteries, and veins) so that blood pumped from Maria Teresa's heart flowed equally into Maria de Jesus, and vice versa.

The birth defect was not lethal, doctors said, but if left attached, the girls would be virtually immobile. Their only hope for a normal life: an operation as rare as the twins' condition. In the past 72 years there have been 31 attempts to separate craniopagus twins--siblings fused at the cranium, the eight bones that make up the skull. Until now, only two surgeries have proved successful. "It was a tremendously risky operation," says chief plastic surgeon Dr. Henry Kawamoto at the Mattel Children's Hospital at UCLA, where the surgery was performed. But the surgeons, who volunteered their services free of charge, had space-age technology on their side.

On August 6, 2002, after a 22-hour marathon surgery, Maria de Jesus and Maria Teresa lay in separate beds--able to see one another's face for the first time. As SW went to press, the two girls were still in stable condition--well enough to smile, eat solid food, even say, "Papa."

Here's an inside look at the miraculous surgery that separated the sisters.

TIES THAT BIND

What's life like conjoined to another human being? The complications are endless. "They were joined in such a manner that they would be condemned to roll--not walk--if they wanted to move from one corner of the room to the other," says UCLA neurosurgeon Dr. Jorge Lazareff. "They'd never be able to go to a movie or simply sit at a table."

The parents had few resources to care for the special needs of their daughters, so for the first 11 months of their lives the twins lived at a pediatric hospital in Guatemala. There the girls slept, ate, drank, even played while attached at the head. To bathe, one sister was held upside down while the other was dipped right side up into the tub. Eating required similar acrobatics.

Few people would dare call the girls "lucky," but the fact that they were born at all is astonishing. About 3 out of every 1,000 pregnancies result in identical twins. The odds that twins will be conjoined are about 100,000 to 1; the odds they will be conjoined at the head--about 2.5 million to 1. Why some identical twins fuse together isn't completely understood, although many experts believe the defect occurs when a single fertilized egg, primed to split in two, stays partially joined.

VISIONARY MEDICINE

On seeing the twins, the first question UCLA doctors asked: Can we separate them safely? In most craniopagus cases, the answer is no. Too much connected brain tissue and overlapping blood vessels make them impossible to untangle. Nine major blood vessels weave through the brain, an organ that uses 15 to 20 percent of the body's total blood supply--more than any other organ (see diagram, p. 13). One leak could stop oxygen-rich blood from reaching brain cells; without oxygen, cells die--a brain-damaging condition called stroke.

To determine whether the girls could survive surgery, doctors relied on some of the most sophisticated medical imaging devices on Earth. "Before 1972, we didn't have the tools to see what was going on inside the patient before operating," says Kawamoto. "We were just sort of going into it blind." Today, medical equipment like the magnetic resonance imaging (MRI) machine generates detailed images of the interior brain--as though surgeons had sliced it in half to peer inside.

The MRI images of the twins revealed two separate brains conjoined not by large clumps of brain tissue but by a handful of blood vessels, some skin, and bone: Separation would be difficult, but not impossible. The girls' parents gave doctors the green light to move ahead", and they began to study the images--along with a computer-generated 3-D plastic model (see image, p. 13)--to map out the safest way to perform the surgery.

THREE DEGREES OF SEPARATION

Although the girls would be surgically parted in a single day, the entire procedure was spread out over several painstaking months, and divided into three general stages. Stage 1 was critical: create extra skin to cover the girls' heads after the operation. Skin, or the integumentary system, is the single largest organ in the body. It forms a watertight barrier against germs and helps the body retain fluids. Skin is also remarkably elastic, thanks to stringy fibers of collagen and elastin.

How do you "create" more skin? "We literally stretched the girls' skin out," says Kawamoto. One month before the surgery a fluid expander--essentially a balloon--was implanted beneath the scalp where the twins' heads met (see diagram, p. 11). Over the next 30 days, saltwater was pumped into the balloon, slowly causing it to expand and stretch the dermis, the deepest skin layer. At the same time the skin stretched, new blood vessels sprouted, which helped rebuild thinned out muscle and fat cells snaking below the dermis.