What is neurosurgery?

Indications and Procedures

Neurosurgery refers to any surgery performed on a part of the
nervous system. Brain surgery may be used to remove a tumor or foreign body, relieve the pressure caused by an intracranial hemorrhage, excise an abscess, treat parkinsonism, or relieve pain. In cases of severe mental depression or untreatable epilepsy, psychosurgery (such as lobotomy) may alleviate the worst symptoms, although these procedures are now rare. Surgery may be performed on the spine to correct a defect, remove a tumor, repair a ruptured intervertebral disk, or relieve pain. Surgery may be performed on nerves to remove a tumor, relieve pain, or reconnect a severed nerve.

Most
brain operations share some common procedures. Bleeding from the numerous tiny blood vessels in the brain is controlled by use of an electric needle, a finely pointed instrument that shoots a minute electric current into the vessel and seals it. (This same instrument can be used as an electric knife for bloodless cutting.) Brain tissue is kept moist by continued washing with a dilute salt solution. The brain tissue itself is handled with damp cotton pads attached to the end of forceps.

If the brain is swollen, it may be treated by intravenous injections of urea. The resulting increase in the salt concentration of the blood draws the water away from the brain. In addition to drawing off excess water, the brain’s size is temporarily reduced, giving the surgeon extra room to maneuver. To help reduce bleeding within the brain, the patient’s blood pressure can be lowered by half temporarily through an injection of a drug into the blood. The patient’s temperature is also reduced, which lowers the brain’s need for oxygen and ensures that the reduced blood flow will not be deleterious.

An operation in which a hole is cut into the skull is called a
craniotomy. If only a small hole is required, the procedure is called trepanation (or trephination) and uses an instrument called a trephine, resembling a corkscrew with a short, nail-like tip and a threaded cutting disk. The size of the opening that is made ranges from 1.5 centimeters (0.6 inches) to 3.8 centimeters (1.5 inches) in diameter and, if necessary, may be enlarged with an instrument called a rongeur. This type of surgery is performed to insert needles or cannulas and to remove subdural hematomas. If too much of the bony skull has to be removed (or is fractured by accidental means), a substitute for the bone is inserted. The substitute is usually made of plastic, such as acrylic.

Brain surgery for advanced Parkinson's disease will not cure the disease but may help alleviate some of its symptoms. The major symptoms are tremor, stiffness, weakness, and slowed movements. For patients who do not respond well to medication, a form of neurosurgery called deep brain stimulation (DBS) can be used to reduce or stop the shaking, by implanting a small device called a brain pacemaker that emits electrical impulses to block abnormal activity in affected regions of the brain.

When pain becomes unbearable, such as the pain associated with cancer, the nerves carrying these pain messages can be interrupted anywhere between the brain and the cancerous region. The nerve to the affected organ can be severed, the nerve roots of the spinal cord can be cut, or the cut can be made within the spinal cord.

Hypophysectomy is the surgical removal of the
pituitary gland. It is usually performed to slow the growth and spread of endocrine-dependent malignant tumors of the breast, ovary, or prostate gland. It may also be used to stop the deterioration of the retina that may come with diabetes mellitus or to remove a pituitary tumor. Hypophysectomy is considered only as a last resort when cryosurgery or radioactive implants fail to destroy the pituitary tissue. There are two ways to reach a diseased pituitary gland by surgery. One way is to go through the nose. The skull is entered through the sphenoid sinus, and the floor of the bony saddle of the middle of the skull is cut to reach the gland. The second means is by craniotomy. The skull is opened through an incision in the hairline above the forehead. A flap of bone, hinged at eyebrow level, is brought forward so that the surgeon can see the entire affected area clearly. The gland is completely excised.

Psychosurgery is now considered only as a last resort, when nothing else can possibly work. It is rarely undertaken because of the availability of so many drugs to control mental illnesses. In the cases when a lobotomy is performed, it can be done under local anesthesia through tiny holes drilled in the roof of the eyes’ orbits. An instrument is then inserted to separate the lobes of the brain.

A laminectomy is performed to relieve compression of the spinal cord caused by injury (the displacement of a bone) or by the degeneration of a disk; it may also be used to find and remove a displaced intervertebral disk. A laminectomy is performed under general anesthesia. The surgeon makes an incision in the back, vertically over the tips of the vertebral bones. The large, thick muscles that lie on either side are peeled back from the surface of the bones. The lamina itself is the part of a vertebral bone that forms the back wall of the spinal canal. When the laminae are cut away, the spinal canal is opened so that the spinal cord covering can be cut. Once the cord is exposed, a particular condition can be treated. It may then be necessary to fuse the vertebrae. The removal of the laminae causes little interference with support or motion of the spine, although recovery from the surgery requires that the patient remain prone for several days to keep the spine in alignment.

Fusion of the vertebrae is the surgical joining of two or more spinal vertebrae to stabilize a segment of the spinal column following severe trauma, a herniated (ruptured) disk, or a degenerative disease. The surgery is performed under general anesthesia. The cartilage pads are removed from between the posterior portions of the affected vertebrae. Bone chips are cut from the vertebral ridges and inserted as a replacement for the removed cartilage. Postoperative motion must be limited until the articulating bones heal.

Severe pain that cannot be controlled by analgesics (painkillers) may be treated by surgery. One procedure, a cordotomy, removes a section of the spinal cord so that most of the nerve fibers that transmit pain messages to the brain are destroyed. At first, the patient does experience less pain, but after a few months, the pain can recur and become worse than before. The recurrence of pain is likely attributable to the reconstruction of some axons that carry ascending messages. Other painful conditions can be treated with surgery. Trigeminal neuralgia (or tic douloureux) is one such condition. These severe attacks of stabbing pain in the face may last a minute or more. The trigeminal nerve can be injected with a concentrated alcohol solution, which will prevent it from working for a year or two. This condition is usually treated surgically by drilling a burr hole in the temple and cutting across the lower two-thirds of the nerve trunk at the site.

A
sympathectomy surgically interrupts a part of the sympathetic nerve pathways. It is used to relieve the pain of vascular disease. The surgery involves removing the sheath from around an artery. This sheath carries the sympathetic nerve fibers that control vasoconstriction. Once the sheath is removed, the vessel relaxes and expands so that more blood travels through it.

Uses and Complications

While neurosurgery offers the hope of recovery to people suffering with tumors, aneurysms, and brain injuries, it may result in complications that can bring disability, coma, or even death. Therefore, three issues must be taken into account before neurosurgery is performed. First, these surgeries involve higher risk than most other procedures. Second, diseases that necessitate neurosurgical treatment may render patients wholly or partially incompetent to understand the implications of their surgery. Third, sometimes matching the appropriate surgery to the patient’s condition is an uncertain process. Even standard neurosurgical procedures have not been proven in every event.

Because the diagnosis of a brain tumor is often seen as fatal, many believe that surgery has little value as therapy, especially for malignant tumors. Others suggest, however, that the more radical the surgery, the greater the chance of survival for the patient. The problem arises when a tumor is found within the center area of the brain, where the primary sensory and motor cortices are situated. Surgical methods of the past tended to exacerbate the problems of the patient. The use of lasers and microscopy, however, may increase the chance of successful treatment. Using these tools, incisions of no longer than 2 centimeters can be made. Using the microscope, the surgeon can guide the laser to the tumor, which is gently melted and vaporized—all without disturbing the brain. This method is especially useful for reaching deep-seated tumors.

Stereotactic surgery is a means by which monitoring devices are inserted into the brain cortex. These devices can detect lesions, stimulate or record areas within the cortex, or in some other way study the brain. The two things necessary to perform this surgery are a stereotactic atlas (or map) of the brain and the instrumentation for the procedure. The atlas is a series of individual maps, each representing a slice of the brain. The stereotactic instrument consists of two parts: a head holder, which maintains the patient’s head in a particular position and orientation, and an electrode holder, which holds the device that is to be inserted.

The purpose of the lesion method of stereotactic surgery is to remove, damage, or destroy a part of the brain in such a way that the behavior of the patient can be monitored to determine the functions of the affected area. Surgery to produce lesions is an extremely precise, and therefore dangerous, surgery. Structures within the brain are tiny, convoluted, and tightly packed, and any surgery performed on an area may therefore damage adjacent areas. There are four different methods of producing lesions.

Aspiration lesions are performed when the target site is in a more accessible area of the brain, where the surgeon can see it clearly and can use the proper instruments. The cortical tissue is aspirated by a handheld pipette, and then the tougher white matter layers are peeled away. Deeper lesions are created with high-frequency (radiofrequency) currents passed through carefully placed electrodes. The heat of the current destroys the tissue. The amount of tissue to be removed is regulated through control of the current’s duration and intensity. In the third method, a nerve or tract to be removed can be cut with a scalpel. A tiny incision severing the nerve does not have to do damage to surrounding tissues, so the lesion is small.

The fourth method is cryogenic blockade. In this method, a coolant is pumped through the tip of an implanted cryoprobe to cool the area. When the tissue is cooled, the neurons do not fire. The temperature must remain above freezing, however, to prevent destruction of the tissue. Although the result is not a true lesion, since function returns, this cooled area acts as a lesion because the behavior that it governs is interrupted. Consequently, cryogenic blockade is said to produce a reversible lesion.

A commissurotomy, or severing the connection between the two cerebral hemispheres, may be performed in cases of severe epilepsy if no other treatment is successful. After the two halves are separated (the brain stem is left intact), each hemisphere maintains all the centers that mediate its functions, except that each cortex sees only half the world. For example, visual messages are crossed so that the opposite hemisphere is stimulated by only one eye’s input. If both eyes and both hemispheres are working, however, vision should be unaffected. In fact, no real deficits should occur in these patients’ behavior. They retain the same verbal intelligence, reasoning, perception, motor coordination, and personality, because of the brain’s extraordinary ability to preserve unity, or
oneness.

Commissurotomies were first performed in the hope of reducing the severity of convulsions and seizures associated with epilepsy. The rationale was that the severity of the convulsions would be reduced if discharges could be limited to the hemisphere from which they originated. The benefits far surpassed expectations; many patients never experience another convulsion.

Perspective and Prospects

Archaeological evidence shows that people living in the Stone Age performed trepanation. This operation was likely performed to release evil spirits or demons: There is little evidence of fractures of the skulls that have been found, and the pieces of skulls that were excised were preserved and worn as talismans. Today, surgeons in some tribal cultures perform the same surgery; in some cases, some are done for ritual purposes, while others are performed for head injuries as well as headache, dizziness, and epilepsy. Trepanation laid the groundwork for brain surgery as it is still practiced.

Perhaps the most intriguing possibility for future research is transplanting brains or brain tissue. Brain transplants have come a long way from their portrayal in science fiction. In 1971, the first real evidence that transplanted tissue could survive was found. These successful attempts were made in rats. Further studies have shown that transplants have a higher survival rate in tissue richly vascularized with sufficient room to grow. It is hoped that neurotransplant surgery can be used to treat brain damage. One approach would be to develop procedures of implantation that would stimulate the regeneration of the patient’s own tissue. A second approach would be to replace damaged tissue with healthy tissue of the same type.

The major question that will have to be answered before successful regeneration is accomplished is why neurons of the peripheral nervous system (PNS) regenerate but the neurons of the
central nervous system (CNS) do not. One hypothesis would be that they are too structurally different. This theory is disputed by studies that show CNS neuron regeneration in the peripheral nervous system, while PNS neurons do not regenerate in the central nervous system. Other evidence to refute the hypothesis is that peripheral sensory neurons regenerate until they reach the spinal cord, then regeneration ceases. Therefore, perhaps there is an environmental factor within the central nervous system that prohibits regeneration, such as scar tissue that forms only in the area of CNS damage. Experiments to prove or disprove this theory are inconclusive. The other possibility is that the insulating cells wrapped around CNS neurons are different enough from the Schwann cells of PNS neurons that
regeneration is discouraged.

Attempts to replace damaged tissue with healthy tissue have been most useful in treating Parkinson’s disease (with its rigidity, tremors, and lack of spontaneous movement). One type of tissue used for replacement is fetal neural tissue. It not only survives but also innervates adjacent tissue, releases neurotransmitters (in this case dopamine), and alleviates the symptoms of parkinsonism. A possible substitute for neural tissue is autotransplantation with some of the patient’s own adrenal medulla. This tissue could be used because it too releases dopamine. Investigations thus far have been controversial, but the operation is being performed worldwide.

Bibliography

Bear, Mark F., Barry W. Connors, and Michael A. Paradiso. Neuroscience: Exploring the Brain. 3d ed. Philadelphia: Lippincott Williams & Wilkins, 2007.

Bloom, Floyd E., M. Flint Beal, and David J. Kupfer, eds. The Dana Guide to Brain Health. New York: Dana Press, 2006.

Daube, Jasper R., ed. Clinical Neurophysiology. 3d ed. New York: Oxford University Press, 2009.

Pinel, John P. J. Biopsychology. 8th ed. Boston: Pearson Allyn & Bacon, 2011.

Post, Kalmon, et al., eds. Acute, Chronic, and Terminal Care in Neurosurgery. Springfield, Ill.: Charles C. Thomas, 1987.

"What Is Neurosurgery?" Patient Education Institute, April 2, 2009.

Zollinger, Robert M., Jr., E. Christopher Ellison, and Robert M. Zollinger, Sr. Zollinger’s Atlas of Surgical Operations. 9th ed. New York: McGraw-Hill, 2011.