Bypass for the Brain

Delicate microsurgery may prevent strokes

With advancing age, as the arteries leading to the brain become more and more clogged by fatty deposits, the chances grow that a clot may form in one of the narrowed passages, cutting off the flow of blood to a region of the brain. The result may be a stroke, which could lead to loss of memory or speech, paralysis, and even death. For this type of patient, few treatments are available, though doctors sometimes prescribe anticoagulants to lessen the chance of clotting. Yet, since 1967, teams of skilled neurosurgeons have been performing exquisitely delicate brain-artery bypass operations on such stroke-prone patients. They have also been meticulously monitoring these patients, comparing their progress with that of others who have not been surgically treated. Their preliminary finding: the operation appears to offer protection against strokes--the U.S.'s third leading cause of death --but further evaluation is needed.

The operation offers little hope for people who have survived major strokes that have caused severe, lifelong disability. It is designed for those who have suffered minor strokes or who show early warning signs of trouble. In these patients the brain-artery bypass may avert death or a crippling attack that would require long and costly rehabilitation.

According to Dr. James I. Ausman, head of the University of Minnesota team that reported on its bypass studies at a recent stroke conference in New Orleans, there are six danger signals that may precede a major stroke: passing episodes, lasting from minutes to several hours, of 1) numbness in a limb or the face; 2) weakness or drooping on one side of the body; 3) speech difficulties; 4) blurring of vision, usually in one eye; 5) dizziness and double vision; or 6) severe headache and a stiff neck. Anyone who experiences such "little strokes" should visit a physician promptly. Many of these premonitory strokes result from a blockage in the internal carotid artery above the jaw line, where it is beyond reach of the scalpel. Thus the obstruction may be treatable only by a difficult bypass, diverting blood to the brain from outside the skull. For this procedure, Ausman and other neurosurgeons use part of the temporal artery, which ascends in front of the ear and then divides, one branch carrying blood to the forehead and the eye socket, the other to the scalp. First they cut and fold down a flap of scalp above the ear. In the process, they sever the artery and separate it from the scalp. (Other vessels supply blood to the region above the severed artery.) Next, they saw out a piece of skull, about the size of a half-dollar, to expose one of the arteries on the surface of the brain. Usually the vessel is a branch of the middle cerebral artery, an extension of the internal carotid.

Now comes some demanding microsurgery. The exposed artery is clamped in two places, leaving a blood-free gap 1 to 2 cm (up to about 3/4 in.) long into which the freed segment of the temporal artery is sewn.

This maneuver requires 20 stitches with thread finer than a human hair and barely visible to the naked eye.

(The blood vessels are so thin--no thicker than an ordinary pencil lead --that the surgeon must peer through a microscope while joining them together.) Then, when the cerebral artery branch is undamped, additional blood spurts into the brain. Finally, the surgeon closes the hole by restoring the skin flap; usually the excised piece of bone is discarded, but patients rarely suffer any discomfort from the soft spot.

Probably 3,000 bypasses have been performed so far, most of them in Switzerland, where the operation originated, and in the U.S., Canada and Germany. Still, doctors point out that these patients have not yet been studied long enough to determine for sure whether the surgery is superior to other treatment or even to none at all. These very questions will now be examined in detail by an international team of neuroscientists led by Dr. H.J.M. Barnett of University Hospital, London, Ont., and financed by the U.S. National Institutes of Health. The team expects to study 1,000 stroke-prone patients in medical centers round the world. Half of them will receive the operation; the other half will get conventional therapy, which in some cases may be nothing more than aspirin. After five years of close observation, the survey should tell whether the operation is really as promising as the preliminary findings indicate.

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