Separating sisters: inside the groundbreaking surgery. (Life/medical science: anatomy/blood vessels).

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.

On August 5 at 8:00 a.m., the twins were ready for Stage 2: the surgical separation. A 50-member surgical unit piled into the operating room and split into two teams--one for each twin. First, with the aid of a "fancy drill" known as a craniotome, the skull was carved open to expose the brains. The next step: untangle and reroute blood vessels back into each girl's head.

Of particular concern was a fat triangular vein called the sagittal sinus. Normally, it wraps over the top of the skull and drains down the back of the head, eventually flushing blood to the heart. But in each sister the vein crossed into the other's head. Detaching it could drastically reduce blood flow to either twin. The best solution: clamp the vessel down slowly, allowing smaller veins to absorb some of the blocked blood flow. "It's like a highway with minor streets running off it," says Kawamoto. "If you block off the main highway too quickly, you'll cause an accident, or in this case death to part of the brain."

At roughly 1:00 a.m. the next morning, the girls were parted. The surgery left a 9 by 14 centimeter-wide opening (about the size of a small envelope) at the top of each skull, exposing the brain like a half-peeled orange. To protect it, surgeons attached a thin layer of soft tissue called dura mater. (The membrane is one of three spongy layers that protects and cushions the brain.) Then they stitched skin flaps over the gaps where the twins' heads were once joined (see diagram, p. 11).

At 5:40 a.m. the surgeons declared the operation a success. "It went like clockwork," says Kawamoto. But while Maria de Jesus rested in stable condition, Maria Teresa was rushed back to the operating room four hours later. Blood leaked from one of her rerouted veins and pooled beneath synthetic dura mater.

The blood buildup, or hematoma, exerted pressure on Maria Teresa's skull and put her at risk for paralysis (loss of body movement). To relieve the pressure, surgeons again sliced open Maria Teresa's skull to drain the blood. Luckily, nearly one month after the procedure, Maria Teresa's recovery is as strong as her sister's. "We feel that the outlook for both twins is very positive," says Dr. Lazareff.

A SEPARATE PEACE

The third stage is yet to come. The final procedure will place a hard protective covering--probably bone spliced from their skulls--over soft tissue covering the gap, but that will have to wait until the girls are at least 6 years old. By that time their heads will have reached 95 percent of their adult size, so "there will be sufficient bone thickness to allow us to split the skull," Kawamoto says.

In the meantime, the twins are busy adjusting to their new independence. Says Kawamoto: "When we asked the nurse if Maria de Jesus was tugging at the bandages, she said, `No, but she did wave her hand over her head, as if to say, Where's my sister?'"

IT'S YOUR CHOICE

Choose the correct answer(s) to these questions:

1 Conjoined twins are always

A identical.
B united at the head.
C separable through surgery.
D formed from two fertilized eggs.

2 The human brain requires what percent
of the body's total blood supply?

A 2 to 7 percent
B 10 to 15 percent
C 30 percent
D none of the above

3 Which statement about blood vessels is true?

A Veins carry blood away from the heart.
B Arteries carry blood away from the
heart.
C Arteries carry blond toward the heart.
D none of the above

1. a 2. d 3. b

THREE STAGES TO SEPARATION

Last summer, a volunteer team of surgeons at UCLA performed three procedures to separate conjoined twins Maria Teresa and Maria de Jesus.

1 Create extra skin

The skin on the twins' heads was stretched to cover the opening after separation. Two months before the separation surgery, doctors implanted one balloon just under the scalp where the heads met. Over the course of 30 days, saltwater was injected into the balloon to stretch the skin.

2 Separate the heads

On August 6, doctors sawed through skin and bone to reroute the twins' common blood vessels back into their own bodies. Before surgery, malformed veins (vessels that carry blood toward the head) crisscrossed into each twin's head.

3 Close the wound

Finally, surgeons covered the twins' brains with synthetic dura mater tissue. The girls were born without the protective membrane, which is normally attached to the inside of the skull.

In about six years

Doctors will permanently cover the opening with bone spliced from each twin's skull.

BLOOD AND THE BRAIN

The brain is one of the hardest working organs in the body. It contains billions of cells that coordinate your every thought and movement--and uses up to 20 percent of the body's oxygen supply, How does oxygen reach the brain? Through a network of blood vessels that carry oxygen-rich blood. Arteries carry blood away from the heart and to the brain. Veins channel blood away from the brain toward the heart.

Did You Know?

* Few twins conjoined at the skull live longer than five years. Only one set is known to have ever reached adulthood.

* Separating conjoined twins is exceedingly dangerous: 75 percent of the time one twin dies as a result of the surgery.

* The first known surgical procedure to separate conjoined twins dates back to 1495. The first documented success, in which both twins survived the operation, was in 1952.

* An estimated 70 percent of conjoined twins are female.

Cross-Curricular Connection

Ethics/Debate: Is it ethical to separate healthy twins conjoined at the head if it's likely that one twin will die in the process? Write an essay to support your answer.

Critical Thinking:

How have medical advances increased the success rate of surgeries to separate conjoined twins?

Directions: Fill in the blanks to complete the sentences.

1. The circulatory system includes --, --, --, and --.

2. The largest organ in the body is the -- system, or --.

3. -- channel blood toward the heart and -- carry blood away from the heart to the brain.

4. To prepare for surgery to separate the conjoined twins, doctors inserted a --, which is like a -- beneath the --. This helped stretch the --, or the deepest layer of skin.

5. Scientists will wait until the twins are -- years old to perform the operation's final step. That's when the head reaches -- percent of its -- size.

Separating Sisters

1. heart, blood, arteries, veins

2. integumentary, skin

3. veins, arteries

4. fluid expander, balloon, scalp, dermis

5. 6, 95, adult

Resources

"After Surgical Separation, Twins' Prognosis Is Good," by Nick Madigan, The New York Times, August 7, 2002. p. A10

Log on to the Web site of Mattel's Children's Hospital at UCLA to learn more about the surgery:

www.healthcare.ucla.edu/conjoined_twins/index;asp

Learn more about brain science at the Washington University School of Medicine Web site for kids: faculty.washington.edu/chudler/vessel.html