At nine o’clock on July 28th last year, Wendy Nissley carried her two-year-old daughter, Lacy, into O.R. 12 at Johns Hopkins Hospital to have half of her brain removed. Lacy suffers from a rare malformation of the brain, known as hemimegalencephaly, in which one hemisphere grows larger than the other. The condition causes seizures, and Lacy was having so many—up to forty in a day—that, at an age when other toddlers were trying out sentences, she could produce only a few language-like sounds. As long as Lacy’s malformed right hemisphere was attached to the rest of her brain, it would prevent her left hemisphere from functioning normally. So Lacy’s parents had brought her to Johns Hopkins for a hemispherectomy, which is probably the most radical procedure in neurosurgery.

Wendy laid her daughter on the operating table. Because Lacy was so small, it took the anesthesiologist almost ninety minutes to insert her intravenous lines. George Jallo, the attending neurosurgeon, spent a long time arranging her head on gel padding and then drew “Cut here” markings on her shaved scalp. The rest of Lacy’s head, including her face, was covered with a sterile drape. Jallo made one long cut across the top of her head from the front to the back, and another at right angles to the first, which started midway along it and stopped just in front of her right ear. He folded back the scalp and made small holes in her skull with a power drill, outlining a rough semicircle. Then he used the drill to connect the dots and removed a portion of the skull. He cut another T in the dura, a thin, leathery membrane covering the brain. Gently, he peeled back two large flaps.

By half past one, Jallo and a resident had already removed the right frontal lobe. David Lieberman, the pediatric neurologist who had examined Lacy when she first came to Johns Hopkins, looked on, shaking his head in wonderment. “It’s so open,” he said, turning to me. “Normally, with brain surgery, you make a hole about this big”—he curled his thumb and index finger into a circle.

After removing the frontal lobe, Jallo embarked on the parietal lobe. In case complications put a sudden stop to the surgery, it was important to take out the seizure hot spots first, gradually working through the hemisphere in descending order of priority: after the parietal lobe would come a small section of the occipital lobe, then the temporal lobe, then the rest of the occipital. Finally, Jallo would cut the corpus callosum, the bundle of fibres that connect the two hemispheres of the brain. The surgeons slowly worked around each side of the parietal lobe, making tiny pinches in the brain with electric cauterizing forceps. There was a slight smell of burning in the bright, noisy operating room. As the cut became deeper and wider, the tissue on either side browned and blackened, and the lobe started to move back and forth. At the bottom of the parietal wedge, the clean white of nerve fibres was visible; as the lobe was severed, they came apart like string cheese. A surgical technician bent toward Jallo with a small plastic bowl in his hands. Jallo picked the lobe out of the skull—it was the size of an infant’s fist—and dropped it into the container.

As she led me out of the O.R., Eileen Vining, the attending neurologist, said, “Did you see how rigid it was? Normal brain sags in your hands.” Vining talked quickly, moving from one complicated idea to the next, punctuating each with “O.K.?” and an expectant nod. She had been in and out of the operating room all morning, and now she was off to find the Nissleys and tell them how Lacy was doing.

Four hours later, Vining took me back into the O.R. Lacy’s right hemisphere was gone, and her cranium looked like a wide, uneven bowl. I could see the deep cavity where the frontal and parietal lobes had been, and the white-pink color inside the base of the skull. In the middle of the remaining brain was a shallow mound where Jallo had left a layer of nerve fibres to protect the ventricle, a fluid-filled pocket that cushions the brain and the spinal cord. The white matter there was now gray-black. Jallo and his resident lightly touched their forceps to it, and the cauterizers fizzed, sealing the brain to prevent microhemorrhages. Hemorrhaging is a constant concern in brain surgery, and at one point in the operation Jallo decided to leave in a small piece of the right occipital lobe which threatened to bleed dangerously. Jallo glanced at Vining and Lieberman, and the doctors stretched forward to look at the severed corpus callosum. Over and over, the surgical technician poured in saline, and Jallo and his resident drew it out again with a loud suction pump.

When he had finished removing brain tissue, Jallo tipped in small packets of Surgicel, a feathery white substance that helps blood to clot. It melted onto the surface of the brain. “That was good. There was not a lot of bleeding,” Vining said. “You never know what you are going to get until you open it up. Sometimes you just go in there and you hold your breath and pray.”

In the final hour, Jallo sutured Lacy’s dura, which had shrunk slightly from dehydration, and filled the right side of her head with saline. The technician then brought the missing section of the skull back to Jallo, carrying it in a wide right angle over surgical carts rather than risk moving it over the floor. Jallo reattached it, using four tiny dissolvable plates made of a sugarlike substance. He then closed the scalp incision with a staple gun, leaving seventy-eight aluminum staples in Lacy’s skin. The hemispherectomy had taken nine hours. The resident bandaged Lacy’s head, gently turned her onto her right side, and stuck a piece of tape on her head that said “This side up.”

I first met the Nissleys three months before Lacy’s surgery, at their home in Palmyra, Pennsylvania. As I drove up, I could see Lacy’s father, Mike, dangling a leg over the edge of the front porch. He looked like a surfer, with a goatee beard and gold-lens Oakleys pushed back on his head. Wendy sat on a chair near the front door, and Lacy’s four-year-old sister, Lily, flitted around the adults. Lacy, blond like her mother, lay across Wendy’s lap. “She had a seizure just before you got here, so she’s sleeping now,” Wendy said. They invited me inside.

Lacy had her first seizure on October 13, 2003, when she was four and a half months old. Wendy had been doing laundry, and when she turned around she saw that Lacy’s lips were blue and that she was shaking. She called 911, but by the time the ambulance arrived the seizures had ended. In the following month, the family went to the hospital many times, but, on each occasion, by the time they got there the spell had ended and there didn’t seem to be anything wrong. The doctors took an MRI but saw nothing unexpected, and they suggested that Lacy might have acid reflux or sleep apnea, or could even be doing it on purpose, out of anger. “But she wasn’t angry,” Mike said. “She was sitting there happy, and all of a sudden it hit her like a train.” One doctor put her on phenobarbital, increasing the dose each time there was another seizure. “It made her lethargic, like she was drunk,” Wendy said. That November, Lacy had a terrible attack. “Her arm went up in the air,” Mike said, throwing his left arm straight up, stiff. “Her lips went blue. She was having them in a row.” By the time the ambulance came, the seizures had subsided, but the attendants advised the Nissleys to get in their car and take Lacy to Johns Hopkins anyway. The drive took two hours, and, just as Mike and Wendy walked over to the triage nurse, Lacy began another cluster of seizures. The nurse said, “We’ve got to get you a room.”

At Johns Hopkins, David Lieberman ordered another MRI. The scan seemed normal, and after a week of further testing Lacy was sent home without a clear diagnosis. Lieberman, in consultation with Eileen Vining and the Johns Hopkins epilepsy group, tried to control the convulsions with medication. Lacy was weaned off the phenobarbital and put on Dilantin and Ativan. They tried Diastat, Topamax, and, later, Tegretol and Keppra. But the seizures continued. When they hit, Mike and Wendy would lay Lacy on the floor and talk to her. “Every couple of minutes, she would moan and groan like she’s in pain,” Wendy told me. Mike nodded. “They said that seizures don’t hurt,” he said. “I don’t know that I believe that.” As we spoke, Lacy sat up a few times and turned to look at me. When I waved and said, “Hi,” she said, “Ba.” Twice, she smiled; once she looked completely terrified. Each time, she turned her shaky head toward her mother and nestled down.

In April, 2004, Lacy returned to Johns Hopkins for four days of continuous EEG monitoring, and again in November for another MRI. The scan showed that she had an enlarged right hemisphere. The bulge on the right made the midline between the two lobes bow slightly toward the smaller side, and there was a strange fogginess on the right side of the scan, whereas the left was clear. Lieberman told the Nissleys about hemimegalencephaly. “We had a diagnosis, finally, and we were happy with that,” Mike said. “It’s not sleep apnea. It’s not acid reflux. It is something. We didn’t know if she was going to die.” Diana Pillas, who coördinates counselling at the Johns Hopkins epilepsy center, told Mike and Wendy about various possible treatments. They could try a ketogenic diet—which is ninety per cent fat and has been shown to stop convulsions in some children—but Lacy would be restricted to a special liquid formula for two years. She also told them about hemispherectomies. “I couldn’t believe it. I didn’t know people could do that and be alive,” Mike said. “The first question I had was ‘Well, what do they put in there?’ ”

After the initial shock, Mike and Wendy decided that the surgery was the best option. Lacy’s seizures had hindered her development to the point where she couldn’t walk unless she was holding someone’s hand, and she hadn’t learned how to chew. The seizures were also becoming more frequent, and they knew that children with her condition tended to live much shorter lives than their peers. The Nissleys were concerned about the costs, though. Mike worked as a butcher at a local supermarket, and Wendy, a doctor’s receptionist, had had to quit working in order to look after Lacy; no day-care program would take her. Johns Hopkins put them in touch with another family whose child had had the procedure, and who told the Nissleys about the financial aid that was available. They finally made a date.

I bumped into Mike and Wendy as I came out of the O.R. with Vining. They were smiling but tense. “We were really stressed,” Mike said later. “We were all wondering if it was the right thing to do. No one said it, but we all knew what we were thinking.”

Neurosurgery began with trepanation, the prehistoric practice of scraping, sawing, or boring a hole in the skull. Trepanned skulls, some as old as ten thousand years, have been unearthed in Europe, Africa, Asia, and the Pacific Islands. Knowledge about the brain’s anatomy has accumulated from the time of Galen, in the second century, but neurosurgery was not recognized as a distinct specialty until the early twentieth century. Since then, neurosurgeons have saved many brains by selectively destroying some of their tissue. They’ve injected brains with pure alcohol, electrocuted them, and inserted wire loops and metal probes and wiggled them about. They have frozen brain tissue, and they have burned it. But no brain surgery is as dramatic as a hemispherectomy. “A hemispherectomy is the opposite of everything you are taught in neurosurgery,” Jallo told me. “You are told throughout your residency training to preserve the brain, get what you have to get, do your work, and leave, but with this you have to take out everything along the way.”

The first recorded hemispherectomy was performed, in 1888, on a dog by Friedrich Goltz, a prominent German physiologist. (Apparently, the post-op animal exhibited the same personality and a minimal reduction in intelligence.) In humans, the operation was pioneered by Walter Dandy, a Johns Hopkins neurosurgeon, who, in 1923, performed his first hemispherectomy on a patient with an aggressive brain tumor in the right hemisphere. The patient lived for three and a half years, until the cancer invaded the remaining hemisphere. Dandy performed another four hemispherectomies, all for patients who had brain cancer in their right hemispheres. In 1938, the Canadian neurosurgeon Kenneth McKenzie performed a hemispherectomy on a child suffering from seizures that could not be controlled with drugs. The operation was a success, and hemispherectomies came to be more popular as a treatment for chronic seizures than for cancer. But eventually the operation fell out of favor. Doctors found that, around ten years after the surgery, some patients became paralyzed or comatose, and sometimes died. This was caused by a buildup of cerebrospinal fluid, a saline-like substance that cushions the brain. The fluid is produced at the rate of about one teaspoon per minute, and in normal brains it is reabsorbed—the total supply of fluid renews itself every five hours. But in some cases the trauma of the operation seemed to prevent this, and the resultant pressure could distort the skull and push the remaining brain to one side, a condition known as hydrocephalus.

The hemispherectomy’s resurgence in popularity is largely the work of John Freeman, a pediatric neurologist who has been at Johns Hopkins nearly his entire career. Tall and charmingly gruff, Freeman is seventy-three and semi-retired, though when I visited him before Lacy’s operation he was still putting in forty hours a week in his cluttered office. “Semi-retired for a workaholic,” he said. Freeman saw a few hemispherectomies while on a training fellowship at Columbia, and started ordering them for patients at Johns Hopkins in the early nineteen-seventies. By then, hydrocephalus could be detected early, with scans, and the excess fluid drained to other parts of the body, where it was reabsorbed naturally. In the early nineteen-eighties, he proposed the treatment, for the first time, for a patient with a diseased left hemisphere—a thirteen-year-old girl who suffered such uncontrollable seizures that she had spent several months in the intensive-care unit. The prospect of removing a left hemisphere—rather than a right one, as had been the case in previous operations—was daunting. It is generally thought that language is situated in the left half of the brain, and no one could say for certain what the effect of removing that hemisphere would be. “We worried about that,” Freeman said. “What would your life be like if you couldn’t talk, and you couldn’t understand, and you were just there and aware?” While a number of the hospital’s faculty approved the operation, an outraged senior physician vetoed it. But the only alternative, Freeman observed, was for the girl to remain in intensive care for the rest of her life, so the following week, when the doctor in question was away, Freeman went ahead and arranged the operation. “Can you imagine doing a hemispherectomy without the assurance that the patient would talk?” he asked. The operation was a success, and the girl recovered the ability to speak. “Now,” he said, “I can tell the families: they all talk.”