Oncologic Disorders of the Brain and Spinal Cord
Oncologic disorders in the brain and spinal cord include several types of neoplasms, each with its own biology, prognosis, and treatment options. Because of the unique anatomy and physiol-ogy of the central nervous system (CNS), this collection of neo-plasms is challenging to diagnose and treat. The pathophysiology, clinical manifestations, assessment findings, and medical and nursing management of brain tumors and spinal cord tumors are discussed in the following sections.
PRIMARY BRAIN TUMORS
A brain tumor is a localized intracranial lesion that occupies space within the skull. Tumors usually grow as a spherical mass, but they can grow diffusely and infiltrate tissue. The effects of neo-plasms occur from the compression and infiltration of tissue. A variety of physiologic changes result, causing any or all of the fol-lowing pathophysiologic events:
· Increased intracranial pressure (ICP) and cerebral edema
· Seizure activity and focal neurologic signs
· Altered pituitary function
Primary brain tumors originate from cells and structures within the brain. Secondary, or metastatic, brain tumors develop from structures outside the brain and occur in 20% to 40% of all patients with cancer. Brain tumors rarely metastasize outside the CNS, but metastatic lesions to the brain occur commonly from the lung, breast, lower gastrointestinal tract, pancreas, kidney, and skin (melanomas).
The cause of primary brain tumors is unknown. The only known risk factor is exposure to ionizing radiation. Both glial and meningeal neoplasms have been linked to irradiation of the cranium, with a latency period of 10 to 20 years after exposure(DeAngelis, 2001). Additional possible causes have been investi-gated, but results of studies are conflicting and unconvincing; suggested causes have included use of cellular telephones, expo-sure to high-tension wires, use of hair dyes, head trauma, dietary exposure to such factors as nitrates (found in some processed and barbecued foods), and other sources (DeAngelis, 2001).
The incidence of brain tumors appears to have increased in the past few decades. Epidemiologic data, however, suggest that this is due more to aggressive and accurate diagnosis rather than to an actual rise in incidence. It is estimated that there are about 17,000 new cases of primary brain tumors per year, 9,600 in men and 7,400 in women (American Cancer Society, 2002). Secondary tumors or metastases to the brain from a systemic primary cancer are more common (DeAngelis, 2001). The highest incidence of brain tumors in adults occurs in the fifth, sixth, and seventh decades, with a slightly higher incidence in men. In adults, most brain tumors originate from glial cells (glial cells make up the structure and support system of the brain and spinal cord) and are supratentorial (located above the covering of the cerebellum). Neoplastic lesions in the brain ultimately cause death by impair-ing vital functions, such as respiration, or by increasing intracra-nial pressure (ICP).
Brain tumors may be classified into several groups: those arising from the coverings of the brain (eg, dural meningioma), those de-veloping in or on the cranial nerves (eg, acoustic neuroma), those originating within brain tissue (eg, gliomas), and metastatic le-sions originating elsewhere in the body. Tumors of the pituitary and pineal glands and of cerebral blood vessels are also types of brain tumors. Relevant clinical considerations include the loca-tion and the histologic character of the tumor. Tumors may be benign or malignant. A benign tumor can occur in a vital area and can grow large enough to have effects as serious as those of a malignant tumor.
Glial tumors, the most common type of brain neoplasm, are di-vided into many categories (DeAngelis, 2001). See Chart 65-1 for the classification of brain tumors. Astrocytomas are the most common type of glioma and are graded from I to IV, indicating the degree of malignancy. The grade is based on cellular density, cell mitosis, and appearance. Usually, these tumors spread by in-filtrating into the surrounding neural connective tissue and there-fore cannot be totally removed without causing considerable damage to vital structures.
Oligodendroglial tumors are another type of glial tumor, rep-resenting 20% of gliomas (DeAngelis, 2001). The histologic distinction between astrocytomas and oligodendrogliomas is difficult to make but important, as recent research shows that oligodendrogliomas are more sensitive to chemotherapy than astrocytomas. These tumors are categorized as low-grade and high-grade (anaplastic).
Meningiomas, which represent 20% of all primary brain tumors, are common benign encapsulated tumors of arachnoid cells on the meninges (DeAngelis, 2001). They are slow-growing and occur most often in middle-aged adults (more often in women). Meningiomas most often occur in areas proximal to the venous sinuses. Manifestations depend on the area involved and are the result of compression rather than invasion of brain tissue. Standard treatment is surgery with complete removal or partial dissection.
An acoustic neuroma is a tumor of the eighth cranial nerve, the cranial nerve most responsible for hearing and balance. It usually arises just within the internal auditory meatus, where it frequently expands before filling the cerebellopontine recess.
An acoustic neuroma may grow slowly and attain considerable size before it is correctly diagnosed. The patient usually experi-ences loss of hearing, tinnitus, and episodes of vertigo and stag-gering gait. As the tumor becomes larger, painful sensations of the face may occur on the same side as a result of the tumor’s com-pression of the fifth cranial nerve.
With improved imaging techniques and the use of the oper-ating microscope and microsurgical instrumentation, even large tumors can be removed through a relatively small craniotomy. Some of these tumors may be suitable for stereotactic radiother-apy rather than surgery.
Pituitary tumors represent about 8% to 12% of all brain tumors and cause symptoms as a result of pressure on adjacent structures or hormonal changes (hyperfunction or hypofunction of the pi-tuitary). The pituitary gland, also called the hypophysis, is a rel-atively small gland located in the sella turcica. It is attached to thehypothalamus by a short stalk (hypophyseal stalk) and is divided into two lobes: the anterior (adenohypophysis) and the posterior (neurohypophysis).
Pressure from a pitu-itary adenoma may be exerted on the optic nerves, optic chiasm, or optic tracts or on the hypothalamus or the third ventricle when the tumor invades the cavernous sinuses or expands into the sphe-noid bone. These pressure effects produce headache, visual dys-function, hypothalamic disorders (eg, disorders of sleep, appetite, temperature and emotions), increased ICP, and enlargement and erosion of the sella turcica.
Functioning pituitarytumors can produce one or more hormones normally produced by the anterior pituitary. These hormones may cause prolactin-secreting pituitary adenomas (prolactinomas), growth hormone-secreting pituitary adenomas that produce acromegaly in adults, and adrenocorticotropic hormone (ACTH)-producing pituitary adenomas that result in Cushing’s disease. Adenomas that secrete thyroid-stimulating hormone or follicle-stimulating hormone and luteinizing hormone occur infrequently, whereas adenomas that produce both growth hormone and prolactin are relatively common.
The female patient whose pituitary gland is secreting excessive quantities of prolactin presents with amenorrhea or galactorrhea (excessive or spontaneous flow of milk). Male patients with pro-lactinomas may present with impotence and hypogonadism. Acromegaly, caused by excess growth hormone, produces en-largement of the hands and feet, distortion of the facial features, and pressure on peripheral nerves (entrapment syndromes). The clinical features of Cushing’s disease, a condition associated with prolonged overproduction of cortisol, occur with excessive pro-duction of ACTH. Manifestations include a form of obesity with redistribution of fat to the facial, supraclavicular, and abdominal areas; hypertension; purple striae and ecchymoses; osteoporosis; elevated blood glucose levels; and emotional disorders.
Brain angiomas (masses composed largely of abnormal blood ves-sels) are found either in or on the surface of the brain. They occur in the cerebellum in 83% of cases. Some persist throughout life without causing symptoms; others cause symptoms of a brain tumor. Occasionally, the diagnosis is suggested by the presence of another angioma somewhere in the head or by a bruit (an ab-normal sound) audible over the skull. Because the walls of the blood vessels in angiomas are thin, these patients are at risk for a cerebral vascular accident (stroke). In fact, cerebral hemorrhage in people younger than 40 years of age should suggest the possi-bility of an angioma.
Brain tumors can produce either focal or generalized neurologic signs and symptoms. Generalized symptoms reflect increased ICP, and the most common focal or specific signs and symptoms result from tumors interfering with functions in specific brain re-gions. Figure 65-1 indicates common tumor sites in the brain.
As discussed, the skull is a rigid compartment con-taining essential noncompressible contents: brain matter, intra-vascular blood, and cerebrospinal fluid (CSF). According to the modified Monro-Kellie hypothesis, if any one of these skull components increases in volume, ICP increases unless one of the other components decreases in volume.
Consequently, any change in volume occupied by the brain (as occurs with disorders such as brain tumor or cerebral edema) produces signs and symptoms of increased ICP.
Symptoms of increased ICP result from a gradual compression of the brain by the enlarging tumor. The effect is a disruption of the equilibrium that exists between the brain, the CSF, and the cerebral blood, all located within the skull. As the tumor grows, compensatory adjustments may occur through compression of intracranial veins, reduction of CSF volume (by increased ab-sorption or decreased production), a modest decrease of cerebral blood flow, and reduction of intracellular and extracellular brain tissue mass. When these compensatory mechanisms fail, the pa-tient develops signs and symptoms of increased ICP. The three most common signs of increased ICP are headache, nausea and vomiting, and a sixth-nerve palsy (DeAngelis, 2001). Personality changes and a variety of focal deficits, including motor, sensory, and cranial nerve dysfunction, are also common.
Headache, although not always present, is most com-mon in the early morning and is made worse by coughing, strain-ing, or sudden movement. It is thought to be caused by the tumor invading, compressing, or distorting the pain-sensitive structures or by edema that accompanies the tumor. Headaches are usuallydescribed as deep or expanding or as dull but unrelenting. Frontal tumors usually produce a bilateral frontal headache; pituitary gland tumors produce pain radiating between the two temples (bitemporal); in cerebellar tumors, the headache may be located in the suboccipital region at the back of the head.
Vomiting, seldom related to food intake, is usuallydue to irritation of the vagal centers in the medulla. If the vom-iting is of the forceful type, it is described as projectile vomiting.
Papilledema(edema of the optic nerve) ispresent in 70% to 75% of patients and is associated with visual disturbances such as decreased visual acuity, diplopia (double vision), and visual field deficits.
The most common focal or localized symptoms are hemiparesis, seizures, and mental status changes (DeAngelis, 2001). When specific regions of the brain are affected, additional local signs and symptoms occur, such as sensory and motor abnormalities, visual alterations, alterations in cognition, and language disturbances such as aphasia. The progression of the signs and symptoms is important because it indicates tumor growth and expansion. For example, a rapidly developing hemiparesis is more typical of a highly malignant glioma than a low-grade tumor (DeAngelis, 2001).
Although some tumors are not easily localized because they lie in so-called silent areas of the brain (ie, areas in which functions are not definitely determined), many tumors can be localized by correlating the signs and symptoms to known areas of the brain, as follows:
· A motor cortex tumor produces seizure-like movements lo-calized on one side of the body, called Jacksonian seizures.
· An occipital lobe tumor produces visual manifestations: contralateral homonymous hemianopsia (visual loss in half of the visual field on the opposite side of the tumor) and visual hallucinations.
· A cerebellar tumor causes dizziness, an ataxic or staggering gait with a tendency to fall toward the side of the lesion, marked muscle incoordination, and nystagmus (involun-tary rhythmic eye movements), usually in the horizontal direction.
· A frontal lobe tumor frequently produces personality dis-orders, changes in emotional state and behavior, and an un-interested mental attitude. The patient often becomes extremely untidy and careless and may use obscene language.
· A cerebellopontine angle tumor usually originates in the sheath of the acoustic nerve and gives rise to a characteris-tic sequence of symptoms. Tinnitus and vertigo appear first, soon followed by progressive nerve deafness (eighth cranial nerve dysfunction). Numbness and tingling of the face and the tongue occur (due to involvement of the fifth cranial nerve). Later, weakness or paralysis of the face develops (seventh cranial nerve involvement). Finally, because the enlarging tumor presses on the cerebellum, abnormalities in motor function may be present.
The history of the illness and the manner and time frame in which the symptoms evolved are key components in the diagno-sis of brain tumors. A neurologic examination indicates the areas of the CNS involved. To assist in the precise localization of the lesion, a battery of tests is performed. Computed tomography (CT) scans, enhanced by a contrast agent, can give specific infor-mation concerning the number, size, and density of the lesions and the extent of secondary cerebral edema. CT scans can pro-vide information about the ventricular system. Magnetic reso-nance imaging (MRI) is the most helpful diagnostic tool for detecting brain tumors, particularly smaller lesions, and tumors in the brain stem and pituitary regions, where bone interferes with CT (Fig. 65-2). In a few instances, the appearance of a brain tumor on an MRI is so characteristic that a biopsy is unnecessary, especially when the tumor is located in a part of the brain that is difficult to biopsy (American Cancer Society, 2001).
In centers where positron emission tomography (PET) is avail-able, it is used to supplement MRI. On PET scans, low-grade tu-mors are associated with hypometabolism and high-grade tumors show hypermetabolism. This information can be useful in treat-ment decisions (DeAngelis, 2001). Computer-assisted stereotactic (three-dimensional) biopsy is being used to diagnose deep-seated brain tumors and to provide a basis for treatment and prognosis. Cerebral angiography provides visualization of cerebral blood vessels and can localize most cerebral tumors.
An electroencephalogram (EEG) can detect an abnormal brain wave in regions occupied by a tumor and is used to evalu-ate temporal lobe seizures and assist in ruling out other disorders.
Cytologic studies of the CSF may be performed to detect ma-lignant cells because CNS tumors can shed cells into the CSF.
Intracranial tumors can produce personality changes, confusion, speech dysfunction, or disturbances of gait. In elderly patients early signs and symptoms of intracranial tumors can be easily overlooked and incorrectly attributed to cognitive and neurologic changes associated with normal aging. The most frequent tumor types in the elderly are anaplastic astrocytoma, glioblastoma multi-forme, and cerebral metastases from other sites. The incidence of primary brain tumors and the likelihood of malignancy increase with age. Signs and symptoms in the elderly must be carefully evaluated because 10% of brain metastases occur in patients with a history of prior cancer (Rude, 2000).
A variety of medical treatment modalities, including chemother-apy and external-beam radiation therapy, are used alone or in combination with surgical resection. Radiation therapy, the corner-stone of treatment of many brain tumors, decreases the incidence of recurrence of incompletely resected tumors. Brachytherapy (the surgical implantation of radiation sources to deliver high doses at a short distance) has had promising results for primary malignancies. It is generally used as an adjunct to conventional radiation therapy or as a rescue measure for recurrent disease.
Intravenous (IV) autologous bone marrow transplantation is used in some patients who will receive chemotherapy or radiation therapy because it has the potential to “rescue” the patient from the bone marrow toxicity associated with high doses of chemother-apy and radiation. A fraction of the patient’s bone marrow is as-pirated, usually from the iliac crest, and stored. The patient receives large doses of chemotherapy or radiation therapy to destroy large numbers of malignant cells. The marrow is then reinfused intra-venously after treatment is completed.
Corticosteroids may be used before and after treatment to reduce cerebral edema and promote a smoother, more rapid re-covery. Gene-transfer therapy uses retroviral vectors to carry genes to the tumor, reprogramming the tumor tissue for susceptibil-ity to treatment. This approach is being tested.
A new technique being investigated is photodynamic therapy. This is a treatment of primary malignant brain tumors that de-livers a targeted therapy while conserving healthy brain tissue (Goodell & Muller, 2001).
The objective of surgical management is to remove or destroy the entire tumor without increasing the neurologic deficit (paralysis, blindness) or to relieve symptoms by partial removal (decom-pression). A variety of treatment modalities may be used; the spe-cific approach depends on the type of tumor, its location, and accessibility. In many patients, combinations of these modalities may be used. Most pituitary adenomas are treated by transsphe-noidal microsurgical removal, whereas the re-mainder of tumors that cannot be removed completely are treated by radiation. An untreated brain tumor ultimately leads to death, either from increasing ICP or from the damage to brain tissue it causes.
Conventional surgical approaches require an incision into the skull (craniotomy). This approach is used in patients with meningiomas, acoustic neuromas, cystic astrocytomas of the cerebellum, colloid cysts of the third ventricle, congenital tumors such as dermoid cyst, and some of the granulomas. For patients with malignant glioma, complete removal of the tumor and cure are not possible, but the rationale for resection includes relieving ICP, removing any necrotic tissue, and reducing the bulk of the tumor, which theoretically leaves behind fewer cells to become resistant to radiation or chemotherapy.
Stereotactic approaches involve use of a three-dimensional frame that allows very precise localization of the tumor; a stereo-tactic frame and multiple imaging studies (x-rays, CT scans) are used to localize the tumor and verify its position (Fig. 65-3). New brain-mapping technology helps determine how close diseased areas of the brain are to structures essential for normal brain function. Lasers or radiation can be delivered with stereotactic ap-proaches. Radioisotopes such as iodine 131 (131I) can also be im-planted directly into the tumor to deliver high doses of radiation to the tumor (brachytherapy) while minimizing effects on sur-rounding brain tissue.
The use of the gamma knife to perform radiosurgery allows deep, inaccessible tumors to be treated, often in a single session. Precise localization of the tumor is accomplished using the stereo-tactic approach and by minute measurements and precise posi-tioning of the patient. Multiple narrow beams then deliver a very high dose of radiation. An advantage of this method is that no surgical incision is needed; a disadvantage is the lag time between treatment and the desired result (Rafferty-Mitchell, Scanlon & Laskowski-Jones, 1999).
The patient with a brain tumor may be at an increased risk for as-piration due to cranial nerve dysfunction. Preoperatively, the gag reflex and ability to swallow are evaluated. In patients with di-minished gag response, care includes teaching the patient to direct food and fluids toward the unaffected side, having the patient sit upright to eat, offering a semisoft diet, and having suction readily available. Function should be reassessed postoperatively because changes can occur.
The nurse performs neurologic checks, monitors vital signs, maintains a neurologic flow chart, spaces nursing interventions to prevent rapid increase in ICP, and re-orients the patient when necessary to person, time, and place. Pa-tients with changes in cognition caused by the lesion require frequent reorientation and the use of orienting devices (personal possessions, photographs, lists, clock), supervision of and assis-tance with self-care, and ongoing monitoring and intervention for prevention of injury. Patients with seizures are carefully mon-itored and protected from injury.
Motor function is checked at intervals because specific motor deficits may occur, depending on the tumor’s location. Sensory disturbances are assessed. Speech is evaluated. Eye movement and pupillary size and reaction may be affected by cranial nerve in-volvement. In one study that examined the experience of brain tumor patients 3 to 5 days postoperatively, the basic needs of patients were met, but changes suggested included minimizing the atmosphere of urgency and hurry, appointing a primary nurse for each patient, and giving more postoperative information (Lepola et al., 2001).
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