Edition: U.S. / Global

Reshaping the Delicate Art of Skull Surgery With a Computer

Published: February 19, 1991

LAST Wednesday, Dr. Craig D. Hall contemplated 7-month-old Lillian Doyle's misshapen skull as it rotated slowly on the screen. He studied the protruding bone on the right side of the forehead, which gave the face a lopsided tilt. He pondered a large, flat patch at the back of her head, a birth defect normally hidden by a shock of strawberry blonde hair.

Sitting in a crisp suit before the computer, Dr. Hall was planning strategy for the complex and messy operation he would perform the next day to refashion the infant's skull.

"In the operating room once I make cuts, I have to use them," said Dr. Hall, a plastic surgeon at Montefiore Medical Center in the Bronx. "But here I try things and if it doesn't work I push a button, trash it and start over. It's a great design tool."

Computer models in three dimensions now allow surgeons to plan and even simulate complicated reconstructive operations of the head, leading to shorter, safer surgery and dramatically improved results. The eerily lifelike pictures that computers can project let the surgeon peer into the skull, pinpoint and measure defects, and construct models of the piece of bone necessary to fill any gaps. On the screen, the surgeon can even test spare parts for fit.

In the past, reconstructive surgeons had to be masters of improvisation, borrowing bits of bone and cartilage ad lib from other parts of the body in the operating room to reshape a skull or recreate a shattered jaw. Because fat and muscle often mask irregular bone, they never knew the full extent of a deformity or how they would correct it until they cut through the skin. The new computer programs have converted the act of improvisation to a carefully rehearsed drama.

"You get much better results," said Dr. H. Steve Byrd, associate professor of plastic surgery at Southwestern Medical School In Dallas. "You know for sure what you are going to do down to the millimeter." In some cases, instructions can be sent from the computer directly to a lathe that, for example, fashions a perfectly fitting plate for a skull defect or a synthetic piece for a damaged cheekbone.

"Many people don't have good enough 3-D perspective to carve freehand in the operating room, " said Dr. Elvin Zook, chief of plastic surgery at the Southern Illinois School of Medicine in Springfield. The technique lets surgeons perform operations that would otherwise lie beyond their skill, said Dr. Zook, who has been using a simulator for two years.

The computer stacks dozens of horizontal slices from two-dimensional CAT scans so as to build up a three-dimensional bust of the subject's skull. The image can then be turned and twisted for inspection simply by giving commands to the computer.

Until now, such simulations have usually had to be run on huge computers that were prohibitively expensive for most operations and awkward for surgeons to manipulate. The Montefiore computer program, made by the Medicad Division of I-Sight Inc. of Orangeburg, N.Y., is at the leading edge of a new generation of inexpensive simulators that can be kept on desktops in offices. The software costs $15,000. Potential for Wide Use

"Now it's a hassle, and that limits its use to the most complicated procedures," Dr. Zook said, noting that the time saved in surgery was more than offset by the hours spent in the computer lab.

"But as programs become easier and cheaper, it's going to be used more and more for routine surgery," he said, maybe even cosmetic operations.

In Lillian Doyle's case, these images aided both in diagnosis and treatment.

Doctors treating children with birth defects often cannot tell even with CAT scans which internal bones are abnormal. Lillian's parents, Laurence and Sharie Doyle of Parlin, N.J., had noticed that her forehead looked crooked when she was 4 months old. Since then, surgeons at more than half a dozen hospitals had offered as many opinions about which bones were defective. "We kept a scoreboard at home to help us decide what to do," Mr. Doyle said. The computer helped resolve the issue.

"Let's take a slice," Dr. Hall said to David E. Acker, who designed the simulator that has been used with rave reviews at Montefiore for the last three months. Mr. Acker had considered the idea of a surgical simulator using CAT scan data for more than a decade, but until 1989 desktop computers were not powerful enough to accomplish the task.

With a flip of a joy stick, Dr. Hall lops off the top of the head on the screen, tilts the skull and studies the craggy contours of bone inside little Lillian's head. A second cut brings into view the abnormally flat quadrant of Lillian's skull, where Dr. Hall can immediately see the problem he previously only suspected: two plates of the skull's bone had fused prematurely, forming a visible ridge and preventing the child's head from growing in the usual curvature. Completely New Perspective

"When you assemble a three-dimensional image," said Dr. Robert Shprintzen, director of craniofacial surgery at Montefiore, "you see things you couldn't possibly imagine by looking at 50 CAT-scan slices of the head, one slice at a time, even with incredible mental gymnastics. It puts a whole new perspective on what's wrong and how to fix it."