Intraoperative Guidance Systems
Just as the space shuttle is guided in mid-flight, so the hand of the surgeon can be guided in mid-operation. Stereotactic guidance systems (involving surface markers or "frames," computers, etc.), three dimensional computer-assisted guidance systems (via infrared lights, lasers, mechanical arms, radiotelemetry), even real-time imaging such as intraoperative ultrasonic guidance systems and MRI, and finally computer guided mechanical arms (hands free) are all available to today's surgeon.
Stereotactic surgery is the use of a special frame that attaches to the skull and serves to guide the surgeon's instruments, electrodes, or cannulae precisely to a local area. The frame is called a stereoencephalotome, which combines the Greek words for solid, head, and to cut; thus, it is an instrument to cut through the solid head. In fact, the stereoencephalotome does no cutting. Instead, it is an instrument with a rounded frame that attaches to the patient's head and can be used to guide instruments at precise angles into the brain.
Once the surgeon has located the area of the brain in which to operate, he places a stereotactic frame on the patient's head. Several types of frame can be used, each of which differs in its type of orientation. Some frames must be oriented with a trephined opening in the skull. Others are oriented using landmarks on the skull such as the ear canals. Once the surgeon has placed the frame over the brain lesion he can position movable arms in the frame to guide electrodes or other instruments into the substance of the brain. Tissue destruction can interrupt pain pathways to reduce pain from cancer or other lesions, which helps the patient better cope with therapy. Certain diseases such as Parkinsonism or hyperkinesis, which involve involuntary movements or shaking can be helped by destroying a small area within the brain. Also, this method can be used to remove a blockage of the drainage system of the brain, which in turn allows the build-up of cerebrospinal fluid and causes hydrocephalus. Removing the tumor blocking the drainage canal or implanting a tube through the canal to drain the fluid relieves the pressure within the skull. Of course, foreign bodies such as bullets also can be located and removed. Precisely focused radiation can be guided by stereoframes to converge on the site of a tumor and destroy it.
As physicians learn more about the brain and the precise location of various functions within it, the use of stereotactic surgery grows. The brain is the only organ that can study itself, and it continues to accumulate knowledge that serves its own best interest in times of illness or injury. With current technology, scientists have begun the implantation of electrodes in the brain to allow the deaf to hear and the blind to see. The electrodes are threaded into the area of the brain that controls hearing or sight and then are connected through a computer to a light or sound receptor. Although this technique is in its early stages, progress in miniaturization of the hardware and the improved knowledge of brain structure and function are combining to make this field a promising venture for the near future.
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