Porth's Essentials of Pathophysiology, 4e

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Nervous System

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and often is worsened by coughing, bending, or sudden movements of the head. Vomiting occurs with or without nausea, may be pro- jectile, and is a common symptom of increased ICP and brain stem compression. Direct stimulation of the vomit- ing center, which is located in the medulla, may contrib- ute to the vomiting that occurs with brain tumors. The vomiting is often associated with headache. Papilledema (edema of the optic disk) results from increased ICP and obstruction of the CSF pathways. It is associated with decreased visual acuity, diplopia, and deficits in the visual fields. Visual defects associated with papilledema often are the reason that persons with a brain tumor seek medical care. Personality and mental changes such as depression are common with brain tumors. Persons with brain tumors often are irritable initially and later become quiet and apathetic. They may become forgetful, seem preoccupied, and appear to be psychologically depressed. Because of the mental changes, a psychiatric consultation may be sought before a diagnosis of brain tumor is made. Focal signs and symptoms are determined by the loca- tion of the tumor. Tumors arising in the frontal lobe may grow to a large size, increase the ICP, and cause signs of generalized brain dysfunction before focal signs are recognized. Tumors that impinge on the visual system cause visual loss or visual field defects long before gen- eralized signs develop. Certain areas of the brain have a relatively low threshold for seizure activity. Temporal lobe tumors often produce seizures as their first symp- tom. Hallucinations of smell or hearing and déjà vu phenomena are common focal manifestations of tempo- ral lobe tumors. Brain stem tumors commonly produce upper and lower motor neuron signs, such as weakness of facial muscles and ocular palsies that occur with or without involvement of sensory or long motor tracts. Cerebellar tumors often cause ataxia of gait. Diagnosis andTreatment The diagnosis of brain tumors relies mainly on MRI. 7,47,50 Gadolinium-enhanced MRI is the test of choice for iden- tifying and localizing the presence and extent of tumor involvement. Computed tomographic scans may fail to reveal certain mass lesions such as low-grade tumors or posterior fossa masses. Diagnostic maneuvers that suggest a possible tumor and indicate the need for MRI include physical and neurologic examinations, visual field and funduscopic examination, and sometimes electroenceph- alography (EEG). Approximately 75% of persons with a brain tumor have an abnormal EEG, which can indicate an underlying structural lesion warranting MRI. Cerebral angiography can be used to visualize the tumor’s vascular supply, information that is important when planning sur- gery. MRI may be supplemented with positron emission tomography to better characterize the metabolic proper- ties of the tumor, which is useful in planning treatment. 54 Magnetic resonance angiography and CT angiography can be used to distinguish vascular masses from tumors. The three general methods for treatment of brain tumors are surgery, irradiation, and chemotherapy.

Surgery is part of the initial management of virtually all brain tumors; it establishes the diagnosis and achieves tumor removal in many cases. However, the degree of removal may be limited by the location of the tumor and its invasiveness. Stereotactic surgery uses three- dimensional coordinates and CT and MRI to precisely localize a brain lesion. Ultrasonographic technology has been used for localizing and removing tumors. The ultrasonic aspirator, which combines a vibrating head with suction, permits atraumatic removal of tumors from cranial nerves and important cortical areas. An important adjunct to some types of surgery is intraop- erative monitoring of evoked potentials. For example, evoked potentials can be used to monitor auditory, visual, speech, or motor responses during surgery done under local anesthesia. Most malignant brain tumors respond to exter- nal irradiation. Irradiation can increase longevity and sometimes can allay symptoms when tumors recur. The treatment dose depends on the tumor’s histologic type, radioresponsiveness, and anatomic site and on the level of tolerance of the surrounding tissue. A newer tech- nique called gamma knife combines stereotactic local- ization of the tumor with radiosurgery, allowing delivery of high-dose radiation to deep tumors while sparing the surrounding brain tissue. Radiation therapy is avoided in children younger than 2 years of age because of the long-term effects, which include developmental delay, panhypopituitarism, and secondary tumors. The use of chemotherapy for brain tumors is somewhat limited by the blood–brain barrier. Chemotherapeutic agents can be administered intravenously, intra-arterially, intrathecally (i.e., into the spinal canal), as wafers impreg- nated with a drug and implanted into the tumor at the time of surgery. ■■ Brain tumors can be divided into primary intracranial tumors of neuroepithelial tissue (e.g., neuroglia, neurons), primary intracranial tumors that originate in the skull cavity but are not derived from the brain tissue itself (e.g., meninges, primary CNS lymphoma, pituitary gland tumors), and metastatic tumors. ■■ The clinical manifestations of brain tumor depend on the size and location of the tumor. Focal disturbances result from brain compression, tumor infiltration, disturbances in blood flow, and cerebral edema. General signs and symptoms include headache, nausea, vomiting, mental changes, papilledema, visual disturbances, alterations in motor and sensory function, and seizures. ■■ The three general methods for treatment of brain tumors are surgery, irradiation, and chemotherapy. SUMMARY CONCEPTS