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Summary Article: Brain Cancer from Encyclopedia of Global Health

In the spectrum of all cancers, brain cancer is a unique entity because it affects people of all ages—brain tumors are the most common cancer of children after leukemias—and has relatively few known causes and risk factors. Brain cancer is also interesting because there are more than 20 different types of primary brain tumors, and the brain is a common location for metastatic cancers from other organs. The most common metastases to the brain are lung and breast cancers.

The most common symptom experienced by people with brain tumors is progressive neurologic deficit, usually weakness. Headaches are the second most common symptom of brain tumors and occur for five different reasons: 1.) increased intracranial pressure (ICP), 2.) high blood pressure secondary to the elevated ICP, 3.) invasion or compression of pain-sensitive structures (e.g., blood vessels) by the tumor, 4.) secondary to difficulty with vision, and 5.) psychological secondary to other symptoms caused by the tumor. Other symptoms may depend on the location of the tumor. If the tumor is supratentorial (above the tentorium cerebelli, the sheet of dura mater that separates the inferior cerebellum from the superior cerebral cortex), other symptoms may include seizures and mental status changes. Infratentorial tumors, on the other hand, may have symptoms of hydrocephalus due to obstruction of cerebrospinal fluid flow.

TYPES OF BRAIN TUMORS

Acoustic neuromas, also known as vestibular schwannomas, are a common brain tumor, comprising approximately 10 percent of primary brain tumors. Acoustic neuromas arise from the vestibular division of cranial nerve VIII (vestibulocochlear nerve). Because this nerve is responsible for hearing function, patients with acoustic neuromas present with symptoms of hearing loss, tinnitus (ringing in the ears), and imbalance. The treatment of acoustic neuroma involves surgery and/or radiation therapy. Common complications after surgery include cranial nerve and brainstem dysfunction, as well as cerebrospinal fluid (CSF) leak.

Astrocytomas are the most common primary brain tumor, and there are many different types of astrocytomas. The World Health Organization (WHO) classifies astrocytomas with a grading system where increased grade equals increased malignancy. Grade I includes pilocytic astrocytoma, grade II low-grade astrocytomas, grade III anaplastic astrocytomas, and grade IV glioblastoma multiforme (GBM). The most common and malignant astrocytoma is GBM; typical survival in patients diagnosed with GBM is one year.

Another interesting clinical entity is brain stem glioma. Brain stem gliomas tend to occur in children and adolescents, and patients typically present cranial nerve palsies, gait abnormalities, and weakness. Brain stem gliomas are very malignant and are associated with poor prognosis; typical survival is from 6 to 12 months.

A positron emission tomography (PET) scan of a 62-year-old man with a brain tumor classified as a grade III astrocytoma.

The choroid plexus is a leafy structure present in the brain’s ventricles that produces CSF. Choroid plexus tumors account for just 1 percent of brain tumors and are primarily a disease of childhood, with 70 percent of patients under the age of 2 years. Some are even found in neonates, suggesting that choroid plexus tumors can also be a congenital condition. These tumors are usually benign but can also be malignant. Because choroid plexus produces CSF, patients usually present with symptoms of hydrocephalus: headache, nausea, vomiting, large head, and so forth. The only option for treatment is surgery.

Central nervous system (CNS) lymphoma may occur primarily, originating in the brain, or secondarily, originating outside the brain and metastasizing to it. Lymphoma is very common and the fifth leading cause of cancer deaths in the United States. Primary CNS lymphoma (PCNSL) is rare, making up only 1 to 2 percent of brain tumors and a similar percentage of lymphoma cases. Although PCNSL is rare, the incidence is rising because of the predilection of AIDS and transplant patients to develop lymphoma. Males are affected slightly more often than females, and the average age at diagnosis is about 50 years old. The most commonly affected locations in the brain are the frontal lobes and the cerebellum. Symptoms are frequently due to spinal cord compression (changes in strength and sensation) and carcinomatous meningitis (multiple cranial nerve deficits).

There are three broad conditions that increase the risk of developing PCNSL. First, collagen vascular diseases such as systemic lupus erythematosus, Sjogren’s syndrome, and rheumatoid arthritis carry a higher incidence of PCNSL than the general population. The second group of patients is immunosuppressed patients, such as the elderly or people with AIDS. Last, infection with Epstein-Barr virus (EBV) has been detected in every case of PCNSL.

The treatment of CNS lymphoma includes radiation therapy and chemotherapy. Unfortunately, the disease carries a very poor prognosis. Without treatment, death usually occurs within two to three months; with radiation alone, average survival is 10 months. Combining radiotherapy with chemotherapy offers the best treatment and greatest chances for longer survival.

Colloid cysts are a type of glioma that are benign, slow growing, and comprise approximately two percent of all gliomas and 1 percent of all brain tumors. These tumors typically arise in the third ventricle of the brain, where they block CSF flow and cause symptoms of hydrocephalus. If the cyst causes sudden blockage, it can lead to sudden death. The most common symptoms due to colloid cysts are headache, gait disturbance, and altered mental status. As with most tumors, the treatment of colloid cysts is surgical.

Craniopharyngiomas are benign brain tumors that arise from a specific portion of the pituitary gland. They make up a small percentage (three to four percent) of all brain tumors. Half of the time, craniopharyngiomas occur in children and the peak incidence is between age 5–10 years. Treatment is surgical, but because of the location of these tumors, the operation is quite difficult and recurrences occur frequently.

Ependymomas arise from ependymal cells which line the brain’s ventricles. These tumors can also occur in the spine. Seventy percent of ependymomas occur in children, comprising 10 percent of all pediatric brain tumors. When occurring intracranially, the average age of diagnosis in all ependymoma patients is approximately 17 years. Intracranial ependymomas are typically benign tumors that arise in the fourth ventricle of the brain. Symptoms commonly include headache, nausea, vomiting, gait imbalance, and vertigo. The treatment of ependymoma is surgical resection followed by radiation therapy. This treatment plan results in a five-year survival rate of 40 percent; the younger the patient is, the worse the prognosis.

Epidermoid cysts are benign tumors that make up 1 percent of brain tumors. They typically arise in the cerebellopontine angle (the junction of the cerebellum and pons) or fourth ventricle of the brain from ectodermal remnants of development. If the cyst ruptures, a condition called aseptic meningitis may result with symptoms such as fever, headache, and stiff neck. Treatment is surgical.

Ganglioglioma is a very rare and slow-growing tumor seen mainly in children and young adults; the peak age of occurrence is 11 years. The tumor can arise anywhere in the nervous system. Patients typically present with seizures that are refractory to treatment with medicines. The treatment of this type of brain tumor is surgical, and the prognosis is good.

Hemangioblastomas (HGB) are the most common tumors that arise in the adult posterior fossa (the posterior-inferior part of the brain, i.e., the cerebellar area). These tumors are benign, and 20 percent arise as part of von Hippel-Lindau disease (VHL). In general, HGB account for 1 to 2 percent of brain tumors, and approximately 10 percent of posterior fossa tumors. The most common location of HGB is the cerebellum. Patients become symptomatic usually in their 20s if they have VHL and their 30s if the HGB is sporadic. Symptoms include headache, nausea, vomiting, and cerebellar findings (i.e., incoordination). Treatment is surgical.

The most common low-grade gliomas are infiltrating astrocytomas (WHO grade 2), oligodendrogliomas, and oligoastrocytomas. Low-grade gliomas usually occur in children or young adults and typically present clinically with seizures. Definitive diagnosis is made with biopsy. Treatment is surgical; when complete excision is not accomplished, chemotherapy is the next line of treatment.

Meningiomas account for 15 to 20 percent of all primary brain tumors. Meningiomas arise from the arachnoid (one of the thin layers covering the brain) and are typically benign and slow growing. The most common location of meningiomas is parasagittal, that is, along the midline that separates the two cerebral hemispheres. The average age of affected patients is 45 years and there is a slightly higher prevalence among females. Meningiomas are also a common finding in patients with neurofibromatosis. Surgery is usually curative if the tumor is completely removed, but recurrence is common: 10 to 15 percent in cases where the entire tumor is removed and 30 percent when total removal is not accomplished. The prognosis, however, is excellent with a five-year survival exceeding 90 percent.

Oligodendrogliomas (ODG) are mainly a tumor of adulthood, as the average age of affected patients is 40 years. They are relatively common and make up one-quarter to one-third of glial tumors; there is a slight predilection for development of ODG in males. ODGs commonly grow in the frontal lobes of the brain, and patients frequently present with seizures, headaches, and mental status changes. The treatment of ODG is surgery when possible and chemotherapy for all patients.

The pineal region of the brain contains the pineal gland. A large variety of tumor types can arise in this region. In pediatric patients, the most common lesions are germinomas and astrocytomas. In adults, however, tumors in the pineal region are more likely to be meningiomas or gliomas. Other lesions include pineocytomas, chemodectomas, and choriocarcinomas, to name a few. Clinically, patients of all ages present with the symptoms of hydrocephalus, that is, headache, vomiting, lethargy, and so forth. The treatment of pineal tumors includes surgery and/or radiation.

Pituitary adenomas are tumors of the pituitary gland that make up one-tenth of primary brain tumors. They affect both sexes equally and typically become symptomatic during a patient’s 20s and 30s. Symptoms of pituitary adenoma result from hormonal or mass effect.

The most common hormones released by pituitary adenomas are prolactin, adrenocorticotropic hormone (ACTH), and growth hormone. Prolactinomas cause amenorrhea (no menstrual periods) and galactorrhea (breast milk discharge) in women, impotence in males, and infertility in both sexes. Pituitary adenomas that secrete ACTH cause Cushing’s disease. Growth hormone-secreting adenomas cause acromegaly in adults and gigantism in children.

Excess ACTH is called hypercortisolism, and hypercortisolism caused by pituitary adenomas is called Cushing’s disease. Other causes of hypercortisolism, including lung and adrenal tumors, produce the same symptoms but are known as Cushing’s syndrome. Physical findings in patients with Cushing’s disease or syndrome include weight gain, hypertension, hyperglycemia, osteoporosis, muscle wasting, and psychiatric changes. Skin findings can include thinning, bruising, and purple stripes (striae). The treatment of pituitary tumors can consist of medicines, radiation therapy, and surgery.

Primitive neuroectodermal tumors (PNET) are tumors that arise from primitive neuroectodermal cells. Although there are several different PNETs, the most important are medulloblastomas. Medulloblastomas account for one-fifth of pediatric brain tumors, and they are the most common malignant pediatric brain tumor. Most occur in the first decade of life with a twofold greater incidence in males. Medulloblastomas usually arise in the cerebellum in the vicinity of the fourth ventricle, and resultant symptoms include headache, nausea, vomiting, and ataxia. The treatment of medulloblastoma involves surgery and radiation therapy, with prognosis being dependent on the extent of surgical tumor removal.

    SEE ALSO:
  • Acoustic Neuroma; Brain Diseases; Breast Cancer; Headache and Migraine; Hydrocephalus; Lung Cancer.

BIBLIOGRAPHY
  • Mark S. Greenberg, Handbook of Neurosurgery, 5th ed. (Thieme, 2001).
  • Andrew H. Kaye; Edward R. Laws, Brain Tumors: An Encyclopedic Approach (Churchill Livingstone, 2001).
  • Michael Prados, Brain Cancer (B.C. Decker, 2002).
  • Joanna Hollenberg Sher; Donald H. Ford, Primary Intracranial Neoplasms (Spectrum, 1978).
  • Charles B. Wilson; Craig H. Yorke Jr.; Victor A. Levin, Intracranial Malignant Growth, Primary and Metastatic (Year Book Medical, 1977).
  • Khoi D. Than, M.D.
    Johns Hopkins University School of Medicine
    Copyright © 2008 by SAGE Publications, Inc.

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