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BLACK IS CAREFUL NOT TO LET HIS EYES PROMISE TOO MUCH, EVEN WHEN THERE IS REAL HOPE |
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In fairness to his predecessors, Black has more going for him
than just a pair of gifted hands and a veneration for the human
brain. He also has access to powerful technology that was
unavailable a decade ago. By the time he is ready to apply his
scalpel to a tumor, Black has already mapped out the cancer in
extraordinary detail. He knows before going in, more precisely
than ever, where the boundary lies between malignancy and
"eloquent brain," the clusters of cells responsible for speech,
perception, motor activity and language.
In Schuler's case, Black began his reconnaissance several days before the actual operation with a technique known as functional magnetic resonance imaging. As in conventional MRI, the patient lies inside a chamber while a powerful electromagnet creates X-ray-like pictures of the inside of the brain. In this case, though, the pictures are taken as the patient deliberately performs actions such as moving limbs, speaking or doing mental tasks. With each action, the blood flows to whatever part of the brain is in use at that moment and "lights up" the relevant areas on the MRI picture. The result is a detailed image of where eloquent brain tissue is located (it is slightly different in each patient). If there is a safe corridor into the tumor and if the cancer does not contain vital brain tissue, it is O.K. to operate. So far, Black has used functional MRI for surgical planning on 30 patients. "If the MRI said it was safe to remove the tumor," he says, "none of those patients turned out to have deficits postoperatively." When he first began using it, standard MRI could make only two-dimensional images of the brain. A couple of years ago, however, the fda approved a 3-D version in which a computer combines up to 50 separate slices to create a single image of brain and tumor; the surgeon can view the tumor from any angle to plan the surgery in minute detail. Not only that-- when the neurosurgeon touches any point on the head with the tip of a penlike device called a stereotactic wand, a marker appears at the corresponding spot on the MRI image, displayed on a nearby screen. "In theory," Black says, "you can follow the dotted lines and just cut the tumor right out." You could, that is, if the brain stayed put, but drugs used to prevent swelling can cause it to shrink slightly. Besides, the brain has a consistency something like that of Jell-O; when tissue is cut, things can shift. So for a last survey of the terrain before removing the tumor, Black uses techniques called somatosensory-evoked potentials and direct stimulation to check on the boundaries between tumor and eloquent brain. The techniques are like two sides of a coin. In the first, Black applies a mild electric current to a part of the body--the wrist, for example--and then touches electrodes to exposed brain areas. It is like an electrician testing a circuit: wherever he picks up current, he knows he has a live connection, indicating that the tumor is entwined with eloquent brain and cannot just be cut out. Otherwise, he is touching inert tumor tissue. Conversely, with direct stimulation, Black applies the current to the tumor and sees if the body twitches in response.
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