Brain and Spinal Tumors
A brain tumor is an abnormal growth of cells (neoplasm) in the skull. A spinal tumor is a growth associated with the spinal cord. Tumors are classified as noncancerous tumors (benign tumors) or cancerous tumors (malignant tumors).
Because the skull is a rigid structure that limits expansion, tumors (both benign and malignant) can exert destructive pressure on neural and support tissues. Although all brain tumors are contained within the rigid skull, tumors can exist within brain tissue (intracranial tumors) or as tumors associated with the outer surface of the brain.
Tumors that initially arise and grow within the brain are termed primary tumors. Most adult brain cancers are not primary tumors, but are the result of primary cancer that has spread from other areas of the body. Most brain tumors in children, however, are primary tumors. The cells that nourish and support the neurons that compose the brain are most often those cells that exhibit the uninhibited division and growth that results in primary tumor formation. A glioma is a tumor that originates in the cells supporting and nourishing brain neural tissue (glial cells). The most common primary brain tumors include gliomas such as astrocytomas, ependymomas, and oligodendrogliomas.
Primary tumors are sometimes associated with specific genetic diseases such as tuberous sclerosis or neurofibromatosis. Tumors can also arise following exposure to a sufficient dosage to carcinogens (cancer-causing chemical substances) or nuclear radiation.
The most observed form of primary brain tumor found in adults within the general population are diffuse fibrillary astrocytomas that are then divided on the basis of microscopic examination of the tissue (histopathologic diagnosis) into three specific WHO (World Health Organization) grades of malignancy: grade II astrocytomas, grade III anaplastic astrocytomas, and grade IV glioblastoma multiform.
Pilocytic astrocytomas are the most common astrocytic tumors found in children. Desmoplastic cerebral astrocytoma of infancy (DCAI) and desmoplastic infantile ganglioglioma (DIGG) are present as large, superficial, usually benign astrocytomas that most commonly affect children under the age of two years.
Other gliomas and astrocytomas include brainstem gliomas (usually found in children) that are a form of diffuse, fibrillary astrocytoma that often follow a malignant course. The pleomorphic xanthoastrocytomas (PXA) are low-grade astrocytic tumors that are often found in young adults.
Subependymal giant cell astrocytomas (SEGA) are a form of periventricular, astrocytic tumor that are usually benign or low grade.
Other benign tumors include meningioma tumors (a fairly common, usually benign class of intracranial tumor affecting the meninges), epidermoid tumors, dermoid tumors, hemangioblastomas (usually benign tumors that occur most frequently in the cerebellum and spinal cord of young adults), colloid cysts, pleomorphic xanthoastrocytomas, craniopharyngiomas, and schwannomas. Schwannomas are not strictly a brain or spinal tumor because they arise on peripheral nerves—but they do grow on cranial nerves, particularly the vestibular portion of the acoustic nerve.
Other tumor forms related to diffuse, fibrillary astrocytomas include oligodendrogliomas and oligoastrocytomas. These cerebral tumors are, however, less common than astrocytomas.
Ependymoma tumors are gliomas that are unpredictable. Ependymomas found in the ventricles can be aggressive and highly destructive; other ependymomas are benign spinal cord tumors. Transformation of ependymomas to more malignant forms is rare.
Tumors of the choroid plexus tumors are also unpredictable. Occurring in the choroids plexus that line most of the ventricular system, they can result in the overproduction of cerebrospinal fluid. As with ependymomas, some are malignant, while others are benign.
Other tumors that are usually malignant include medulloblastomas (a highly malignant tumor usually found in children), atypical meningiomas, and hemangiopericytomas (tumors of the dura that may become aggressive and metastasize.)
Brain and spinal tumors are sometimes associated with diseases or disorders. For example, multiple hemangioblastomas are associated with von Hippel-Lindau disease (VHL), an inherited tumor syndrome. Neurological tumor syndromes are those in which patients are genetically predisposed and, therefore, at an increased risk for developing multiple tumors of the nervous system.
Brain and spinal tumors occur in people of all races and sexes, but are slightly more common in Caucasian people than other races. About 40,000 people are diagnosed with a brain tumor each year in the United States. Overall, brain tumors tend to occur more frequently in males than females. Meningiomas, however, occur more frequently in females. Most brain tumors occur in people over 70 years of age, and most brain tumors in childhood occur before age eight. Brain and spinal cord tumors in children are the second most common form of childhood cancer, with about 1,500 children developing these tumors each year. Family history may be predictive, especially with regard to chromosomal abnormalities or changes that may result in the loss of tumor suppressor genes. People with family members who have glioma may be at higher risk of developing a brain tumor.
Long-term exposure to certain chemicals may increase the risk of developing a brain tumor. People exposed to acrylonitrile and vinyl chloride while manufacturing some textiles and plastics, pathologists exposed to formaldehyde, and workers in the nuclear industry may all be at higher risk of developing malignant brain tumors.
Almost 10,000 Americans are diagnosed each year with a spinal cord tumor. Primary spinal cord tumors are rare; most are the result of metastasis (spread) from another site of primary cancer in the body. Most primary spinal tumors are not malignant, but as they occupy space surrounding the spinal cord, they may cause pain and disability.
Causes and symptoms
With the exception of a few genetic syndromes associated with tumors of the brain and spinal cord, the cause of primary nervous system tumors remains a mystery. As most malignant brain tumors are secondary tumors that result from primary cancer that has spread from elsewhere in the body, factors known to influence the development of other cancers, such as smoking, may be considered related causes.
Although not all of the molecular mechanisms are fully understood, there have been dramatic advances in understanding the causes of the cellular transformations of normal healthy cells into tumor cells (tumorigenesis) within the brain.
Present molecular models identify specific genes that play a role regulating the cell cycle and that data indicate that they play a role suppressing tumor growth (tumor suppressor genes such as the p53 gene). Damage to the gene or loss of the chromosome on which it resides (chromosome 17) correlates to the initiation of astrocytoma tumorigenesis. Oncogenic viruses that interfere with tumor suppressor genes have also been linked to tumor formation. More research is needed into the mechanisms of tumor cell transformation before a definitive link can be established.
Other potential causes of brain or spinal cord tumor development under investigation include head injury, occupational exposure to chemicals, and viruses. Additionally, scientists continue to research the possibility of a relationship between cell phone use and malignant tumors of the central nervous system. As of mid-2004, no relationship has yet been established between cell phone use and increased rates of brain cancer.
Symptoms of brain tumors include headaches, nausea, vomiting, seizures, and disturbances in vision and hearing that cannot be related to a disorder of the external sensory organs. Changes in personality and developmental problems, motor problems, and balance problems are also characteristic of tumors.
Spinal cord tumor symptoms often include pain, invalid sensory inputs such as numbness in the toes, feet, or legs, and motor coordination problems.
Brain and spinal tumors may be diagnosed by a combination of neurological examination and imaging such as magnetic resonance imaging (MRI) scans, computed tomography (CT) scans, and positron emission tomography (PET). Other diagnostic tests include laboratory tests (including blood and spinal fluid analysis), myelography, radionucleotide bone scan, biopsy, and microscopic examination of tissues.
Brain and spinal tumors are usually confirmed by computerized axial tomography (CAT) scan, or via the more accurate MRI or PET scans.
MRI scans provide the ability to image and anatomically pinpoint tumors of the brain and spinal cord and thus
provide accurate diagnosis without surgery. Both the MRI and CAT scans produce segmental images of the brain that allow physicians to determine the location and extent of tumors, as well as the extent of damage to neural or surrounding tissue. PET scans use a glucose-and-tracer mixture that is injected into the bloodstream to form a picture of metabolic activity of the brain. As tumor tissue uses more glucose than normal tissue, the tumor presents a brighter image than normal tissue in the picture generated by the scan.
At the tissue level, the presence of cell division at the time of histological examination (tissue exam) is indicative of a higher grade tumor. The greater the rate of mitotic activity (cell division), usually the greater potential for a tumor to advance to a higher and more dangerous type.
GBM tumors are characterized by densely packed cells and the highest high rates of mitotic division. Other tumors such as other gliomas and astrocytomas are diagnosed on the bases of histological examination.
Tumors of the human brain and spinal cord can also be differentiated based on molecular genetic studies that link specific changes in tumors to underlying chromosomal and gene changes (e.g., inactivation of a particular tumor suppressor gene).
In addition to the primary physician, neurologists, and neurosurgeons, treatment often involves oncologists, chemotherapists, and radiation oncologists who can assist the patient and family with treatment decisions. Physical, occupational, and respiratory therapists provide specialized care, as do nurses. Social service consultants coordinate hospital care and community support services.
Treatment for brain and spinal tumors is specific to the type of tumor, location of the tumor, and general health of the patient. Surgery, radiation therapy, and
Surgery involves removing as much of the tumor as possible without damage to the surrounding tissues of the brain or spinal cord. Many benign tumors are encapsulated in sac-like membranes or are single structures that can be completely removed. Surgeons use specialized instrumentation and techniques to remove tumors that are irregularly shaped, near vital structures, or are almost inaccessible.
Stereotactic surgery allows surgeons access to tumors in areas of the brain that are difficult to reach. Using computer-assisted instrumentation, surgeons are guided by a three-dimensional map of the brain to remove tissue or implant radiation pellets into the tumor site. Ultrasonic aspirators break up tumor tissue using sound wave pulses, and the tumor fragments are then removed from the brain by suction.
Microsurgery involves a microscope that gives the surgeon a large view of the operative field in the brain or spinal cord. This reduces the possibility of removing surrounding tissue and injuring critical structures. Electrodes inserted into nerves during surgery evoke the potential, or demonstrate the role of specific nerves, thus guiding the surgeon to avoid damage.
Shunting devices are also placed to divert the blocked or excess flow of cerebrospinal fluid that sometimes occurs with a brain tumor. The ventriculoperitoneal shunt is most often used, and is placed in the ventricles of the brain to divert cerebrospinal fluid to the abdomen. Shunting is frequently required with brain tumors in children.
If the tumor is malignant or is in an area of the brain or spinal cord that would cause critical damage to the nervous system, radiation therapy, chemotherapy, or experimental therapies may be recommended. Radiation therapy involves beams of radiation that are aimed at tumor cells to kill them. Traditional radiation therapy is usually given in six-week courses, and involves some damage to surrounding tissues. Radiation therapy using gamma knife technology, also called stereotactic radiosurgery, is much more precise, and focuses approximately 200 beams of gamma radiation guided by MRI at precise points in the tumor simultaneously. Gamma knife technology reduces damage to surrounding tissues.
Chemotherapy drugs are usually given orally or are injected intravenously, and work to kill rapidly dividing cells. As cancer cells divide more rapidly than normal cells, chemotherapy drugs are effective in killing cancer cells. The side effects most associated with chemotherapy, including nausea, hair loss, and skin problems, result from normally dividing cells that are killed along with the cancer cells. Combination chemotherapy drugs are often prescribed for the treatment of brain tumors, such as BCNU and CCNU. Some of the latest chemotherapy modalities use wafers and pumps to deliver chemotherapy drugs directly into tumor tissue.
Steroids are also prescribed in treating brain or spinal cord tumors to reduce swelling the brain tissues. Anticonvulsants are given to control seizures. A number of other supportive measures are used to relieve pain and combat unwanted side effects of treatment such as medications used to reduce irritation and relieve nausea during radiation and chemotherapy.
Recovery and rehabilitation
After surgery and other treatments for a brain or spinal cord tumor, patients are monitored for recurrence of the tumor or new tumor growth on a regular basis. Initially, CT or MRI scans are done in periods ranging from one to three months. Later, scans are usually decreased to every six months.
Counseling and cognitive therapy can help with the memory problems and personality changes that some people experience after treatment for a brain tumor. Physical therapy and occupational therapy are useful after treatment for a spinal cord tumor to help with any deficits in mobility, reaching, and positioning. Speech therapists can help with challenges in communication. Physical changes in the structure of the brain after treatment may affect the way a child learns, and a neuropsychologist is often helpful in identifying weaknesses and compensation strategies to ease a child's return to school.
Persons with recurrent tumors or tumors resistant to treatment are often offered participation in an experimental protocol or clinical trial. Experimental treatments include gene therapy that introduces substances into the brain tumor, changing the genetic makeup of the tumor cells. Another experimental therapy involves new forms of brachytherapy, where radioactive pellets are implanted directly into the tumor.
The scientific community continually conducts clinical trials in the effort to find new drugs and treatments that are effective against cancer, including those types most often occurring in the brain and spinal cord. As of mid-2004, the National Institutes of Health (NIH) and related agencies were sponsoring more than 200 ongoing studies and trials specific for the treatment of brain and spinal cord tumors. Updated information on these and other trials can be found at the NIH website for clinical trials at <http://www.clinicaltrials.gov>.
Symptoms of malignant brain and spinal cord tumors are usually progressive over time. Symptoms become more pronounced and troublesome as tumors invade or otherwise obstruct healthy tissue. Benign tumors can also cause severe dysfunction by placing pressure on surrounding vital structures, but with treatment, they have a more favorable prognosis.
The slowest growing and least serious of these tumor types, grade II astrocytomas (a "low grade" tumor) can still infiltrate surrounding tissue and thus hold a potential for malignancy. Grade III anaplastic astrocytomas are more malignant than type II tumors. This increase in malignancy translates into lower long-term survival rates. Many persons with grade III anaplastic astrocytomas die within two to three years, while may people with the grade II astrocytoma show long-term survival beyond five years.
Patients with the most severe form of astrocytoma (glioblastoma multiforme, or GBH) usually show survival times of less than two years. Patients with oligodendrogliomas and oligoastrocytomas have generally better prognoses than the diffuse astrocytomas. Brainstem gliomas (a form of pediatric diffuse, fibrillary astrocytoma) have a tendency toward malignancy, and survival beyond two years is unusual. Because PXA tumors are usually slow growing and superficial, they are therefore more likely to be successfully treated by surgical removal.
Primary tumors of the spinal cord are often benign, and surgical removal results in a favorable prognosis. With metastatic spinal tumors, prognosis depends on the type of primary cancer.
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