Neurosurgery
Neurosurgery
Intraoperative guidance systems
Neurosurgery, sometimes also called neurological surgery, is a medical specialty concerned with the diagnosis and treatment of the central and peripheral nervous system. It also involves the surgical operations on the brain and spinal column. These procedures involve such activities as cutting out tumors from the brain and repairing slipped discs in the spine.
The nervous system is composed of the brain, spinal cord and spinal column, as well as the nerves that travel through all parts of the body (hands, legs, arms, face). Neurosurgeons treat degenerative and congenital diseases of the spine, pain from pinched nerves in the neck, lower back pain, sciatica, carpal tunnel syndrome, epilepsy, stroke, Parkinson disease, chronic pain and sports injuries of the head and spine, in addition to brain tumors, hemorrhages and trauma, tumor of the pituitary gland, and disorders of the arteries that carry blood from the heart to the brain. The field of neurosurgery encompasses both adult and pediatric patients. Neurosurgery has one of the longest training periods of any medical specialty due to the extreme complexity of the nervous system and the advanced techniques used in neurosurgical operations.
Neurosurgery may have begun in the early stages of human evolution. Skulls of early humans show signs of incision through the bone. Some skulls have as many as five openings cut into them. Some of this ritual was probably for magical purposes and some was medicinal, performed to release the spirits that were causing excruciating headaches or making an individual show signs of insanity, or to remove bone fragments resulting from trauma. This process is called trephination (less commonly, trepanation) and was a common procedure as early as the Neolithic period. Interestingly, this procedure was done in human settlements around the world. These clans or tribes had no contact with each other, yet they devised and practiced a similar procedure as a form of spiritual or medical therapy.
Trephining was accomplished with a sharpened flint moved in rapid circular motions to cut through the bony skull. The procedure took about a half hour on a drugged patient. It is likely that early humans had discovered the means to immobilize an individual so that surgery could be carried out. Trephining was practiced as late as the mid-twentieth century among isolated peoples. Even cadavers were trephined to remove bone fragments, which were then worn as amulets.
Needless to say, the survival rate of trephination was low. However, skulls have been found that show bone growth around the edges of the opening, indicating that the patient survived for a time after the procedure. More often, skulls with trephined openings show the raw, incised edges of the operative area, indicating that the patient probably died during surgery or shortly thereafter. Infection was not understood and was a high probability following surgery in such conditions.
It was not until the late nineteenth century that further progress was made in the field of neurosurgery. In November 1884, two British surgeons, Alexander Hughes Bennett (1848–1901) and Richman John Godlee (1849–1925), operated to remove a brain tumor. Shortly thereafter, in 1888, English scientist Sir Victor Horsley (1857–1916) removed a tumor from the spinal cord of one of his patients. That same year American surgeon William Williams Keen (1837–1932), of Philadelphia, Pennsylvania, removed a meningioma, a hard, slow-growing tumor that grows on one of the membranes covering the brain. In 1889, Keen tapped the ventricles of the brain, the small openings at the base of the brain where fluid collects.
The development of the x ray provided a means for neurosurgeons to find tumors growing in the brain, bone splinters, or other foreign objects. Still, it remained difficult to locate these growths precisely enough for surgical removal. The invention of stereo-tactic frames to provide precise guidance to underlying tumors helped revolutionize surgery on the brain.
Application of neurosurgery
Current neurosurgery includes trephination along with other procedures to correct not only injury and disease of the central nervous system, but also to modify nerve supply to other areas of the body that may benefit from such surgery and to enhance blood supply to the brain. A number of conditions are commonly treated by neurosurgery. Injuries of the skull, brain, vertebral column and spinal cord are common diagnoses in neurosurgery and are most commonly caused by motor vehicle accidents or sports accidents.
Injury to the head or spinal column may result in swelling of the enclosed nervous tissues, bleeding inside the skull that would place pressure on a localized area of the brain, or may involve bone fragments impinging on the brain or spinal cord as a result of a blow to the head or back. Certain congenital conditions such as hydrocephalus (excessive fluid on the brain) or spina bifida (a condition in which the spine has not closed around the spinal cord) frequently are treated by the neurosurgeon. Premature closure of the skull, which will prevent the skull from expanding as the brain grows, also requires surgery to separate the skull bones.
Tumor growth in the skull or spinal column may also require surgical correction. A benign (non-cancerous) tumor in the brain is usually well defined and can be removed by delicate surgery. A malignant (cancerous) tumor presents a much more challenging problem because it is not defined as clearly and may contain a benign growth as well. Still, some areas of the brain remain unreachable by surgical tools and a growth in those areas cannot be removed. In that case, the physician may resort to radiation therapy or the use of anti-tumor drugs.
The brain requires an especially copious blood supply. Large arteries in the side and back of the neck carry blood to the brain, but when these arteries become narrowed or blocked by fatty deposits (a condition called atherosclerosis), the blood supply to the brain may be reduced to an insufficient amount. A balloon catheter may be used by the physician to clear the blockage. In this procedure, called angiography, a catheter is guided to the site of blockage. The tiny balloon on the end of the catheter is inflated to press the blockage out of the way. The balloon is then deflated, and the catheter removed. In the event this procedure is not effective, the surgeon may need to operate on the blood vessels instead of the brain itself. A graft to bypass the blocked area may be called for or the vessel may be opened and the deposit removed (a procedure called endarterectomy) if the artery is accessible. In addition, an artery can balloon from the pressure of the blood within it. This is called an aneurism, and it forms at the site of a weak spot in the arterial wall. The swollen artery in itself may do no harm, but the weakened arterial wall can burst at any time, allowing the escape of blood into the brain. This is one form of stroke. If the artery is accessible, the surgeon can remove the weak area and sew the ends of the artery together again. If the artery cannot be reached for surgical correction, some means can be taken to reinforce the arterial wall from within.
A so-called slipped disk or ruptured disk, damage to one of the cartilaginous disks between the vertebrae, may form a protrubance into the spinal canal that impinges on the spinal cord. This may cause pain or even the inability to walk normally. Here again, the neurosurgeon may need to take steps to remove the protrusion and in some cases fuse the vertebrae to prevent their flexing on the weakened disk.
In cases of intractable pain or involuntary movements that cannot be corrected, the surgeon may be called upon to interrupt the nerve supply to a given area. This function is being taken over more and more by medical therapy as physicians learn new information about nerve functions and how to interrupt them medicinally, but the surgeon still provides a needed service.
Locating a tumor or area in which blood has been released inside the skull requires a rigorous diagnostic procedure. If the patient has had an accident such as a fall or automobile wreck in which he/she struck his/her head, the surgeon may be more aware of the possibility of the existence of a blood clot forming on the brain, bone fragments that may be impinging on the brain, or swelling of the brain. If the patient denies any accidental trauma to the head, but has had persistent and longstanding headaches, visual disturbances, dizziness, or other lingering symptoms, the surgeon is alerted to the possibility of an aneurism or other source of blood leakage or a developing tumor.
Diagnosis
The diagnosis of the source of a brain disorder has become infinitely more precise with the modern technology of computerized tomography (CT) and magnetic resonance imaging (MRI) scans. Either of these scans shows several views of the brain and the presence of a tumor, excessive fluid build-up, or intracranial bleeding. They also provide the means for precise measurement of the depth of the growth and its angle from various landmarks on the skull. This enables the neurosurgeon to use a stereotactic frame to guide his instruments precisely to the site of the lesion.
The CT or MRI scan shows a cross section of the brain at a certain level. Each exposure is slightly advanced from the previous one. In all, the images appear to be slices of the brain that show various details at each level. The computer control also allows the images to be combined to form a three-dimensional image so the physician can see the tumor or damaged area of the brain in relation to the complete structure. In this way, the surgeon can decide whether the patient is a candidate for surgery or whether the tumor or other lesion is not accessible. The image also gives a good idea of whether the tumor is a cancerous lesion or is benign.
Advances in neurosurgery
Diagnostic accuracy allows the surgeon to work precisely where he or she wants to work with amazing efficiency and reliability, each and every time. The result is that the surgical incision has been reduced to an absolute minimum. Smaller incisions, less tissue trauma, and better surgical planning have reduced the overall risk of brain surgery from almost 90% in the 1940s to about less than 2% in the twenty-first century.
A groundbreaking medical advance of recent years, is the Leksell gamma knife. This revolutionary new treatment is a safe, effective, and cost-efficient alternative to conventional neurosurgery for certain patients. Developed in 1968 by Swedish professors Lars Leksell (1907–1986) and Borge Larsson, the gamma knife is a highly advanced instrument used to treat arteriovenous malformations (AVM), facial pain, benign and malignant brain tumors, and other functional brain disorders. What makes the gamma knife so unique is that it successfully treats these conditions with no incision. Instead, it uses a concentrated radiation dose from Cobalt-60 sources. A total of 201 beams of radiation intersect to form a powerful tool focused on a targeted area of abnormal tissue within the brain. The gamma knife is so precise that it damages and destroys the unhealthy tissue while sparing adjacent normal, healthy tissue.
Intraoperative guidance systems
Just as NASA’s 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/she 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/she 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 buildup 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.
See also Neuron; Neuroscience.
KEY TERMS
Cannula (plural: cannulae)— A hollow tube inserted into an area of the body to drain fluid, guide an instrument, or provide a means to measure pressure or temperature.
Hyperkinesis— Excessive movement or motor activity. A syndrome that results from a brain lesion and leads to fidgeting, nervousness, constant movement, short attention span, and other symptoms in adolescence.
Neolithic period— The geological period that began approximately 12,000 years ago. It was during this period that humans developed advanced stone tools and began forming farming societies.
Neuro— Refers to the nervous system, including the brain, spinal cord, or the nerves leading to and from them.
Resources
BOOKS
Barow, Daniel L., et al., eds. Fifty Years of Neurosurgery. Philadelphia, PA: Lippincott Williams & Wilkins, 2000.
Connolly, E. Sander, et al. Fundamental of Operative Techniques in Neurosurgery. New York: Thieme Medical Publishers, 2000.
Kaye, A. H. Brain Tumors: An Encyclopaedic Approach. Churchill Living, 2001.
Silver, John R. History of the Treatment of Spinal Injuries. New York: Kluwer Academic/Plenum Publishers, 2003.
PERIODICALS
Ganz, J.C. “Gamma knife radiosurgery and its possible relationship to malignancy: a review.” Journal of Neurosurgery. 2002 Dec; 97(5 Suppl):644–52.
Levivier M, Wikler D Jr, Massager N, David P, Devriendt D, Lorenzoni J, Pirotte B, Desmedt F, Simon S Jr, Goldman S, Van Houtte P, Brotchi J. “The integration of metabolic imaging in stereotactic procedures including radiosurgery: a review.” Journal of Neurosurgery. 2002 Dec; 97(5 Suppl):542–50.
Larry Blaser