About 20 percent of all cancers affect the brain and central nervous system, but only a relatively small number about 13,700 cases a year actually arise in those vital areas. The majority of brain tumors are the result of metastases of other cancers, particularly from the lung and breast. The cause of primary brain cancer is unknown but heredity and cancer-causing genes (oncogenes) may play a part, especially in children. Brain tumors present several difficult problems that set them apart from other cancers. Perhaps most important is the fact that the brain is the seat of our intelligence and emotions.
The idea that intelligence and consciousness are threatened is hard for both patient and family to accept. On the positive side, considerable progress has been made in widening our understanding of the effects of brain tumors and their treatment on the patient’s mind and ability to function. Still, even though many brain tumors are either curable or potentially curable, on the whole, cancers of this organ remain an unsolved medical challenge.
THE MASS EFFECT
The contained physical environment within the skull and spinal column leads to problems not usually encountered with cancers of other organs.
Although cancer can destroy vital brain tissue, the major problem encountered in all brain tumors, benign or malignant, is related to their crowding, or “mass effect.” Because they are enclosed within the skull and vertebral column, the tumors have a very limited area in which to grow. Pressure from the expanding tumor can displace adjacent structures, with repercussions to numerous other organs and body functions. Not very much tumor is required to produce a mass effect. A mass as small as 100 grams (3.5 ounces) within the confines of the brain can prove fatal, perhaps a tenth of what the body can tolerate elsewhere. The mass effect is much the same for benign tumors as for malignant; the only difference may be that malignant tumors tend to grow much faster than benign ones.
The fibrous structures that divide the brain cavity into several major compartments
present additional barriers to tumor movement and consequently cause other impairments in function. Shifts, or herniations as they are often called, can develop in these compartments, leading to impaired function that often is undetected in the early stages because the signs may be very subtle. Displacement of the lower part of the brain that joins the upper part of the spinal cord disrupts the control of the basic physiologic processes of respiration, blood pressure, and heart rate. Pressure on these structures can become a medical emergency requiring rapid intervention by medical and, if necessary, surgical means.
The mass effect causes other problems besides displacement. As the tumor grows, it causes swelling and a buildup of fluid (hydrocephalus). This results in decreased blood circulation, first in small vessels near the tumor and, as pressure increases, to the entire brain. The heart attempts to maintain adequate flow to the brain by increasing blood pressure, but this is usually not enough. The flow of cerebrospinal fluid, which bathes and cushions the central nervous system, is also impeded.
Evidence of high cerebral pressure can be seen when a doctor looks into the back of the eye with a simple hand-held ophthalmoscope. The optic nerve, which is actually an extension of the brain rather than being a true nerve, will often be visibly engorged and swollen a condition called papilledema because of the high pressure behind it.
Partial obstruction of the flow can result in increasing hydrocephalus, in which the accumulation of cerebrospinal fluid increases while the brain itself is slowly compressed.
Signs that this is happening may include apathy, diminished spontaneity, slowed thought processes, sleepiness, instability in walking, incontinence, headaches, and seizures. Most tumors of the brain and spinal cord, whatever the specific location and type, will eventually produce a mass effect if they are not diagnosed and treated.
The diagnosis of brain tumor is not always easy or evident because the onset of symptoms may be gradual, vague, and only recognized in retrospect. Headache is a common symptom but, contrary to popular belief, it is not always severe or persistent. Instead, the pain may be vague and variable in pattern. Often, the pain can be relieved by aspirin, acetaminophen, or other moderate painkillers. If the tumor invades or stretches the meninges the nerve-rich membranes covering the brain and spinal cord the headaches will be more severe. Some are similar to migraines. If there are general characteristics associated with the headache of brain tumors, they are that the pain is perceived as being deep and it is often worse at night or early in the morning. The apparent location of the headache is not truly a good indicator of the tumor site. Nausea and vomiting unrelated to food occur in about 25 to 30 percent of brain tumor patients, frequently in association with headache.
Sometimes a seizure in a person over forty years of age who never has had one before is a warning sign of a possible brain tumor or metastases to that organ. The seizure is caused by increased pressure, which “irritates” nerve tissue near the tumor.
The effects of a brain tumor on other parts of the body are strongly correlated with the site of the tumor and its pattern of growth. A tumor of the cerebellum, the part of the brain that helps control coordination of movement, will result in progressive movement difficulties, such as an unsteady gait. Analogously, a tumor originating in the centers that control speech or vision will first produce symptoms involving those functions: blurred or double vision, slurred or difficult speech.
shows the parts of the brain where various functions are controlled. Even before CT scans and other sophisticated imaging methods were available, neurologists often were able to pinpoint the location of a tumor simply on the basis of the patient’s symptoms and a thorough neurologi cal examination a rather strange medical drill using things like pins, tuning forks, colored charts, memory and other simple mental tests, and the familiar reflex hammers.
Probably the most frequent signs of a brain tumor, however, are subtle changes in personality, memory, and intellectual performance. These changes are variable and puzzling to the patient, who may be aware of them and make attempts to hide them or compensate for the problems they cause. The changes are often dismissed by friends and family members as trivial or growing idiosyncrasies until they can no longer be ignored. Unexplained changes in personality and mental function always should be investigated. Of course, not all such changes are due to a brain tumor, but the possibility should be ruled out at an early stage.
Accurate diagnosis is particularly important because many brain tumors are benign and potentially curable. Even in instances of cancerous or metastatic tumors, treatment can relieve the symptoms and extend life and improve its quality, even if a cure is not achieved. Sometimes it is difficult to differentiate a stroke from a cancer. Not all strokes come on suddenly; some may evolve slowly, mimicking the gradual development of a tumor. Conversely, hemorrhage into a small, symptom less tumor may enlarge it, suddenly causing it to mimic a stroke.
The diagnostic work-up of a suspected brain tumor usually will include CT scans of the brain as well as conventional X rays. Even with CT scans and other new imaging techniques, surgery may be required for an accurate diagnosis. Although neurosurgery is not always necessary to diagnose a tumor nor is it clearly expected to help the patient, the fear of missing a curable problem is a compelling reason to undergo it. This does not apply when there is proven cancer in other organs; in such instances metastases to the brain usually can be presumed to be the cause of the tumor.
A patient with a suspected brain tumor should be evaluated by a specialist, usually a neurologist or a neurosurgeon. Most hospitals with about 300 beds or more will have a neurologist and neurosurgeon on staff. Patients in smaller institutions that do not have a neurologist should probably be referred to one that does, at least for the more complex parts of the diagnostic work-up and treatment. Most neurosurgeons are associated with several hospitals and perform the more complex procedures at the larger institutions, often hospitals with neurology and neurosurgery teaching programs.
After the patient’s medical history has been obtained and a general physical examination performed, a neurological examination will be carried out. This examination, which may appear odd and even absurd, involves testing the different modes of sensation and awareness, coordination and intellectual function. For example, we normally know where a finger is or the direction in which a foot is pointing without even looking. During the test, a patient may be asked to bring the two index fingers together without looking or to walk forward or backward with eyes closed. The actual actions requested of the patient walking heel-to-toe, rotating the hands as quickly as possible, looking up and down, responding to pinpricks, feeling tuning forks vibrate, and answering simple questions—are all calculated to give the examining physician an idea of the state of the entire nervous system. This examination, when performed by an experienced neurologist, can pick up very small abnormalities or defects that the patient and family may not yet be aware of.
Sometimes metastasis to the brain is the first sign of an undetected cancer elsewhere in the body. The general physical and laboratory examination should pay special attention to determining whether there is a hidden cancer elsewhere in the body, especially one that has a high probability of early metastases to the brain. The breasts in women, testicles in men, kidneys in both, and lungs in smokers deserve special attention. Much more common, however, is the development of metastatic brain cancer in the patient who has earlier undergone treatment for cancer in another organ. In fact, 80 percent of all cases of metastatic brain cancer fall into this category; only 20 percent involve previously undiag-nosed cancers.
New imaging techniques that enable a doctor to “see” inner structures of the brain without resorting to surgery have revolutioned diagnostic neurology. The neuroradiologist, a specialist in imaging the brain, is now a key member of the diagnostic team. CT scans are almost routine in diagnosing brain tumors, but many older tests, such as electroencephalograms (EEGs), cerebral arteriograms, and pneumoencephalograms still may be valuable. Eventually magnetic resonance imaging (MRI), a still-experimental technique that produces images without ionizing radiation, may be even more useful than CT scanning in giving physicians enough information about the location, size, and number of masses within the head.
Cerebral angiography, which entails injecting a dye into the carotid artery and then taking X rays to define the extent of the mass by outlining abnormal blood vessels feeding it, is generally reserved for patients for whom precise surgical planning is required. There is some risk involved in injecting the dye into the cerebral circulation.
Pneumoencephalography, the injection of air into the ventricles, the cavities of the brain normally occupied by spinal fluid, is now rarely performed, and is reserved for small tumors of the pituitary and pineal glands as well as investigating obstruction in the flow of spinal fluid. This examination can be highly uncomfortable and often produces severe nausea and vomiting, and has largely been replaced by CT scanning.
Radionuclide scanning is useful to distinguish a stroke from tumor, but is not a substitute for a CT scan if definite information is required. EEGs, which are generally interpreted by the neurologists, show abnormal electrical waves and can demonstrate a tendency toward seizures.
Another test that is frequently required in diagnosing a neurological problem is a spinal tap or lumbar puncture. Many people needlessly fear this test because they have heard it is dangerous or painful. Both are exaggerations: there is little or no discomfort. The test takes about fifteen minutes from start to finish, can be performed on an outpatient basis or at the patient’s bedside, and it involves very little risk except in unusual circumstances. To do a spinal tap, a thin, hollow needle is inserted between two vertebrae in the lower back.
A small amount of spinal fluid is withdrawn and sent to the laboratory for analysis. Increased protein, evidence of blood, or abnormal cells suggests the presence of a tumor. Sometimes a headache may occur after a spinal tap, but this usually can be avoided by lying in bed for a few hours after the procedure.
A spinal tap can be hazardous if there is increased intracranial pressure because of tumor mass. In this instance, a sudden reduction of pressure because of a spinal tap can cause a rapid shift of brain structures with serious, even fatal, consequences. But most brain tumors give evidence of their presence long before they are large enough to make a spinal tap unsafe. In any event, CT scanning has reduced the need for many spinal taps, and like any invasive procedure, the test should be performed only if the information to be gained will significantly alter the treatment plan.
A biopsy is not usually performed, even though there may be neurological symptoms and an identifiable mass. (An exception might be to diagnose diffuse or degenerative neurological disorders, such as multiple sclerosis or Alzheimer’s disease.) Instead, neurosurgery may be planned, at which time a definitive diagnosis of whether the tumor is benign or cancerous is made and treatment is carried out. This might range from complete removal of the mass and a cure, to reduction in tumor mass and relief of the intracranial pressure. Neurosurgery probably will not be advised for metastatic disease or for patients whose general medical ; condition does not indicate a good outcome.