Malignancy and the Nervous System
Diagnosis
Probable glioblastoma multiforme; left frontal lobe.
Malignancies may affect the nervous system in a variety of ways. Primary and metastatic tumors may affect the brain, spinal cord, and peripheral nervous system directly. Distant tumors may affect various neurologic systems due to metabolic changes, or due to paraneoplastic effects. Radiation may cause injury to radiosensitive neural structures. Chemotherapies have a variety of effects on nervous system tissues. Patients with malignancies are often at increased risk of stroke. Finally, nutritional disorders in cancer patients can lead to injury to the nervous system.
SIGNS AND SYMPTOMS OF BRAIN TUMOR
These signs and symptoms apply to primary and metastatic central nervous system (CNS) tumors.
Does the patient have headache? Headache is one of the most common symptoms, present in approximately two thirds of patients. It often occurs in the morning, when intracranial pressure is higher.
Other signs and symptoms include seizures, personality changes, hemiplegia, and visual disturbances. Mental changes, especially memory loss and decreased alertness, are often important subtle clues of intracranial tumor.
Patients may have a gait disturbance.
Seizures associated with tumor are characteristically focal. They may be “Jacksonian”—a focal seizure that begins in one extremity, then “marches” along one side of the body. It may become a generalized convulsion. New-onset seizures in a middle-aged adult are often caused by a brain tumor.
Check for papilledema, or sixth-nerve paresis caused by increased intracranial pressure.
PRIMARY BRAIN TUMORS
Primary brain tumors, although uncommon, are a significant cause of death in middle-aged adults. The most common types are glioblastoma multiforme, astrocytoma, meningioma, and pituitary adenoma. Primary central nervous system (CNS) lymphoma is becoming more common, particularly in patients with acquired immune deficiency syndrome (AIDS).
Glioblastoma Multiforme (GBM)
Glioblastoma multiforme comprises 20% of all intracranial tumors. It is usually located in the hemispheres in adults, with peak incidence in middle age. It may present with headache, seizure, or a personality change. It is a neoplasm of astrocytic-type cells, and is a vascular tumor with irregular enhancement on MRI and computed tomography (CT). Irrespective of treatment, it carries a poor prognosis for long-term survival.
Astrocytoma
Astrocytoma is a slower-growing astrocytic tumor with a better long-term prognosis than GMB, but cure is rare. Astrocytoma may form large cysts. In approximately half of patients, it presents with seizures.
Meningioma
Meningioma is a benign tumor of the dura, located over the surface of the brain (convexity, wing of the sphenoid, skull base), in
the spinal canal as an intradural/extramedullary lesion, and rarely in an intra-ventricular location. It is more common in women and in the elderly. Thoracic spinal meningioma occurs particularly in elderly women. Meningiomas enhance on MRI and CT, and angiography shows a tumor blush.
the spinal canal as an intradural/extramedullary lesion, and rarely in an intra-ventricular location. It is more common in women and in the elderly. Thoracic spinal meningioma occurs particularly in elderly women. Meningiomas enhance on MRI and CT, and angiography shows a tumor blush.
Pituitary Adenoma
Pituitary adenoma is an endocrine tumor that may cause amenorrhea, acromegaly, Cushing disease, or rarely, hyperthyroidism. It may be nonsecreting, causing symptoms by pressure on the optic chiasm and/or normal pituitary gland. Classically, it causes a bitemporal hemianopsia (loss of temporal fields of vision) because of compression of the nasal retinal fibers passing through the chiasm.
Primary Central Nervous System Lymphoma
Primary CNS lymphoma is a B-cell tumor with a periventricular localization that may involve the eye in 20% of cases. (Vitreous biopsy may be diagnostic.) It is common in patients with AIDS, and occurs in other immunosuppressed patients. It is often deep in the brain and usually multicentric. It is rapidly progressive, and treated by stereotactic biopsy, radiation, steroids, and chemotherapy. It is usually unresectable. In patients infected with the human immunodeficiency virus, it may be difficult to distinguish lymphoma from toxoplasmosis; stereotactic biopsy may be helpful. Prognosis is poor when AIDS is present. Because steroid therapy may lyse CNS lymphoma, delay use of steroids until after biopsy if CNS lymphoma is suspected.
INTRACRANIAL METASTASES
Which Tumors Invade the Brain?
Up to 25% of patients with cancer have cerebral metastases at autopsy. Metastatic tumor reaches the brain through hematogenous spread, and generally after first invading the lung. This accounts for the high incidence of intracranial metastases with lung and breast tumors. Other tumors that metastasize to brain include melanoma, hypernephroma, and GI malignancies
LABORATORY INVESTIGATION FOR BRAIN TUMOR
MRI with gadolinium enhancement is the most sensitive test for detection of brain tumor, especially in the posterior fossa. Contrast-enhanced MRI is particularly useful if leptomeningeal metastases are suspected.
Arteriography is rarely necessary for diagnosis. Arteriography may be helpful before surgery on a meningioma to delineate the vascular supply of the tumor.
There is increasing use of stereotactic brain biopsy as a method of establishing the correct diagnosis with low morbidity; particularly for lesions that are not considered resectable. However, pathologic diagnosis sometimes may be difficult, because of the small amount of tissue obtained with this kind of biopsy.
TREATMENT OF BRAIN TUMOR
The treatment of primary brain tumor depends on the tumor type and location:
Meningiomas are usually surgically removable.
Low-grade astrocytomas and oligodendrogliomas are best treated by surgery plus irradiation.
High-grade astrocytomas (glioblastoma multiforme) are treated by resection plus irradiation or, depending on location, partial removal plus irradiation. There is increasing use of chemotherapy—such as l, 3-bis-(2 chloroethyl) 1-nitrosouria (BCNU) intravenously, or as Gliadel wafers implanted at the time of resection—which prolongs survival. Adjuvant chemotherapy may be useful in oligodendroglioma and astrocytomas. Chemotherapy trials are available for most patients with primary brain tumor.
Tumors showing symptomatic mass effect may be treated with dexamethasone.
Newer radiotherapy techniques have included radioactive implants and stereotactic radiosurgery (linear accelerator or gamma knife).
In meningiomas, surgical resection of this tumor is usually curative, unless only partial removal is possible or anaplastic pathology is present. Certain meningiomas that are benign cannot be completely resected because of their location, such as in the cavernous sinus or growing into the sagittal sinus.
In pituitary adenomas, treatment is surgical; other treatment modalities include radiotherapy and endocrine replacement therapy. Prolactin secreting tumors may respond to suppression of prolactin release by dopamine agonists.
In primary CNS lymphomas, a multidrug-chemotherapy combination, including methotrexate, procarbazine, vincristine, dexamethasone, and cytarabine plus radiation therapy, has been shown to produce an increase in median survival of 41 months. This is compared with 10 months for patients receiving radiotherapy alone. Newer regimens with high-dose methotrexate have also been used.
In patients with metastatic brain tumor, one must first determine whether the brain is involved by single or multiple metastases. MRI with gadolinium is the most sensitive test. Documented multiple metastases are treated with steroids and whole brain irradiation. Symptoms are ameliorated with steroids to reduce cerebral edema. One randomized study showed similar efficacy using dexamethasone 1 mg. q.i.d. and 4 mg. q.i.d., with a reduced side-effect profile in the low-dose regimen. Higher doses are used for impending herniation. Irradiation improves length and quality of survival. Chemotherapy may be added.
Treatment of a single metastasis is surgical, if the patient is a good operative candidate and the lesion is surgically accessible. In addition to offering palliation, other disease processes sometimes are found at operation (e.g., subdural hematoma, brain abscess, primary brain tumor). Radiosurgery provides another approach to single metastases less than 3 cm in diameter, and is sometimes used with 2 to 4 metastases.
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