As a fledgling pilot, William Welch knows he must keep track of his position in all three dimensions as he approaches a landing. A mistake of a few feet up or down can mean disaster.
As a neurosurgeon, Welch can keep track of only two dimensions with his surgical microscope. Yet as he and his chief resident, Dr. Bruce Pollock, operated on a woman's upper spine several weeks ago, he knew a slip of a few millimeters could mean death or disability.If their instruments went too deep, they would enter the medulla oblongata, the part of the brainstem that controls breathing, heart beat and blood pressure. Too far to the side, they could breach a vertebral artery.
Relying only on their microscope would be like landing an airplane without knowing its altitude.
So Welch and Pollock relied on a computer, not just their eyes, to guide them as they jockeyed their instruments in the back of the woman's mouth. Throughout the four-hour operation, a pointer superimposed on a computer monitor over a three-dimensional image of the woman's head worked like a "You are here" arrow on a road map.
It's called image-guided surgery and Welch, a neurosurgeon at the University of Pittsburgh Medical Center, predicts it will become the standard of care for brain and spinal surgery in as little as three years.
The systems make surgery safer and often can reduce the size of incisions, damage to healthy tissues and the length of a hospital stay.
"It's very slick," agreed Dr. Robert Selker, chief of neurosurgery at Western Pennsylvania Hospital.
The six-figure price tags for the systems may give hospital administrators sticker shock, he admitted, but he thinks Welch's three-year prediction is too conservative.
"It's coming so fast, it's unbelievable," Selker said.
Dr. Richard Bucholz, a neurosurgeon at St. Louis University School of Medicine, said the cost will decline as computer prices continue to drop. And demand for the devices from surgeons is building.
"It's like having airbags in your car," Bucholz said. "Once you have them, you don't feel safe without them."
Today's imaging technology, such as computerized tomography scans and magnetic resonance imaging (MRI), can show the presence of a tumor or other structural problem inside the head with amazing clarity. But when surgeons open up a patient's skull, they may have trouble discerning healthy tissue from diseased tissue, or even finding a malformation that is obvious on the image.
One way surgeons have tried to bridge this gap between image and reality is stereotactic surgery. A circular metal frame is bolted to the patient's head and a CT scan of head and frame is made. A computer then calculates the position of, say, a deep-seated tumor relative to the stereotactic frame. Markings on the frame are then used to guide surgical instruments to the tumor's location.
The latest technology, however, eliminates the need for a frame. The computer is able to use physical landmarks, such as the tip of the nose, or a corner of an eye, as well as "fiducials" - tiny foam doughnuts glued to the head - to match reality with a three-dimensional image of the patient's head.
The surgeons can then check their progress during surgery by using a special wand that is mechanically or optically linked with the computer. When they place the tip of the wand at the surgical site, the computer senses the location of the wand and superimposes it over the computerized image.
"Instead of telling you how to get someplace," like conventional stereotaxy, "it tells you where you are," Welch said.
Though sometimes called "frameless stereotactic surgery," some surgeons say that's like calling a car a horseless carriage. Image-guided surgery is far more flexible than stereotactic surgery and some researchers already are exploring how image guidance can be married to robots to automate some surgeries.
Surgeons at Pitt, West Penn and Allegheny General Hospital say they routinely use the image-guided systems.
Welch and Pollock also were looking for added safety as they operated several weeks ago. Their patient's head was slowly detaching itself from her spine and the operation was the first of two needed to reattach it.
The patient, a woman in her 40s who asked that her name not be used, was suffering deterioration of her spinal column. Welch said decades of kidney dialysis appeared to have caused metabolic changes contributing to the deterioration.
The problem was most severe at the second cervical vertebra, which is shaped like a fist with the thumb extended up. The thumb, or odontoid process, forms the pivot on which the head turns. But her odontoid process was crumbling, allowing her head to shift forward on her neck and compress her spinal cord.
For years she had suffered a bizarre symptom called Lhermitte's sign: whenever she bent forward, an electrical shock passed through her body.
The symptom is named after Napoleon's battle surgeon, who first described the symptom in soldiers with partial spinal injuries. When the soldiers were moved, severing the spine, they would report feeling an electrical charge.
Doctors advised surgery, but the woman resisted for years. Gradually, she lost control of her hands and upper arms. Four days before finally entering the hospital for surgery, she lost the ability to walk. By the time of surgery, she was becoming a pentaplegic - losing control of not only all four extremities, but also the swallowing muscles of her lower skull.
Welch needed to fuse several cervical vertebrae to secure the head, but first had to remove deteriorated bone and a fibrous tumor that had developed as the head shifted forward.
The woman's head and neck were immobilized in a surgical halo. She then had a CT scan from which the computer assembled a three-dimensional image of her head that showed both the tumor and the deteriorated bone.
In the operating room, Pollock touched the tip of the positioning wand to facial landmarks and to fiducials that had been glued to her face prior to the CT scan. The wand was connected to a mechanical arm which relayed the position of the wand to the computer. The computer was then able to "register" the 3-D image with her head.
Throughout the operation, they periodically checked their progress with the positioning wand. As a double check, they also used a fluoroscope, an instrument that makes X-ray images that can be viewed immediately on a video monitor. In the past, the fluoroscope would have guided surgeons in such an operation.
But Welch pointed out that where the computer showed - and surgeons found - diseased odontoid bone, the fluoroscope showed nothing.
"Here's an example where the wand is saying we're `on,' but the fluoro tells us we're `off."'
Once the tumor and the diseased bone were removed, her spinal cord began to decompress and she regained strength in her extremities, Welch said. Four days later, in a second surgery, he fused her neck bones in two places.
Believing what a computer says exists in a patient's head and neck, based on a CT scan and not on the eyes or other instruments, can lend an air of unreality to an operating room, said Dr. Matthew Quigley, a neurosurgeon at Allegheny General.
One of the challenges, in fact, is discerning what is real and unreal about the information the computer spews. The images that the computer uses to guide the surgery are taken prior to surgery. Bones can usually be secured, so their positions don't change. But fluids are lost and soft tissues can change position once surgery begins.
"The longer the operation goes ... the less valuable the image becomes," Quigley said.
This spring Allegheny General will install an experimental MRI system that lets doctors perform surgery as the patient lies inside the MRI machine. The magnetic resonance images that guide the surgery can then be updated as the operation proceeds.
Image-guided surgery already is being enhanced in other ways. St. Louis' Bucholz, who developed a system called Stealth Station, said surgeons soon will no longer need to take their eyes off the patient to view a computer monitor. Head-mounted video displays are being tested, as are systems that project the computer display into the surgical microscope.
The technique is not limited to use in the head and spine. In St. Louis, for instance, surgeons have begun using it to perform prostate surgery, Bucholz said.
(Distributed by Scripps Howard News Service.)