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·         gait   [gate]   Pattern of walking.

·         Gamma Knife   Brand name of a machine that delivers stereotactic radiosurgery (SRS), a focal form of radiation therapy.

·         ganglia   [gang´ lee ah]   A mass of nerve tissue (gray matter), or a group of nerve cell bodies. Also refers to specific groups within the brain or spinal cord (as basal ganglia). Ganglion is the singular of ganglia.

·         gangliocytoma   [gang´ lee o sigh toe´ ma]   A rare, benign tumor arising from ganglia-type cells, which are groups of nerve cells. Most frequently occurs in children and young adults. Also called a ganglioneuroma.

·         ganglioglioma   [gang´ lee o glee o´ ma]   A rare, benign tumor arising from mature nerve and supportive cells.

·         ganglioneuroma   [gang´ lee o nur o´ ma]   A rare, benign tumor arising from ganglia-type cells, which are groups of nerve cells. Most frequently occurs in children and young adults. Also called a gangliocytoma.

·         GAO   US Government Accounting Office.

·         gastrointestinal tract   [GI]   The stomach and intestines. See digestive system.

·         GBM   Glioblastoma multiforme. A grade IV astrocytoma that commonly invades adjacent tissue and can spread widely within the brain. Its hallmark is areas of dead tumor cells (necrosis) found within the tumor. The GBM represents about one-quarter of all primary brain tumors. The abbreviation favored by the World Health Organization is GB (glioblastoma).

·         gemistocytic astrocytoma   [je miss toe sih´ tik • as tro sigh toe´ ma]   A subtype of the astrocytoma, this tumor contains gemistocytes — plump glial cells that have undergone apoptosis. Their presence is associated with more frequent recurrences and progression to a higher grade of tumor.

·         gene   The unit of heredity found on a chromosome, genes are pieces of DNA that contain the information to perform a specific function. Each gene occupies a specific location on a chromosome.

·         gene amplication   The number of copies of a gene is increased; often seen in malignant cells.

·         gene deletion   The absence of a specific gene on a chromosome.

·         gene therapy   Treatment that seeks to replace or repair defective or abnormal genes; biologic response modification.

·         generalized seizure   Refers to several types of seizures: absence seizure; atonic seizure; tonic-clonic seizure; myoclonic seizure.

·         generic   [je ner´ ik]   A drug not protected by a trademark. Also, the scientific name as opposed to the proprietary, brand name.

·         genesis   [jen´ eh sis]   The beginning of a process.

·         genetic   [je net´ ik]   Inherited. Passed from parents to children through genes in sperm and egg cells.

·         genetic markers   Alterations in DNA that might indicate an increased risk of developing a disease, or are associated with the presence of a disease.

·         genome   [je’ nome]   A complete set of chromosomes.

·         germ cell   A sperm or egg; a sex cell; a cell whose purpose is to reproduce the organism.

·         germ cell tumors   Tumors that begin in the cells that give rise to sperm or eggs. They can occur anywhere in the body and can be either benign or malignant. Germ cell tumors of the brain arise in the pineal or suprasellar regions. They include the germinoma, the teratoma, the embryonal carcinoma and yolk sac (endodermal sinus) tumors, and the choriocarcinoma. Mixed germ cell tumors also exist.

·        germinoma   [jer mih no´ ma]   The most frequent tumor of the pineal region and the most common type of germ cell tumor in the brain. It typically occurs in the pineal or suprasellar region of the brain.

·         GFAP   Glial Fibrillary Acidic Protein. This protein, found in microfilaments of glial cells, helps distinguish glial from non-glial tumors. A laboratory stain is used to test for its presence.

·         giant cell glioblastoma   A variant of the glioblastoma multiforme tumor.

·         gigantism   A disorder in children due to an excessive amount of growth hormone. Growth hormone, also called somatotropin, is secreted by the anterior lobe of the pituitary gland. A hormone secreting pituitary adenoma, a type of benign brain tumor, can cause this condition. In adults who have achieved their full height, excessive growth hormone causes acromegaly.

·        gland   An organ of the body that produces materials (hormones) released into the bloodstream, such as the pituitary or pineal gland. Hormones have a widespread effect on the body and can influence metabolism and other body functions. Part of the endocrine system.

·         Glasgow Coma Scale   A means of describing the severity of brain impairment. Can the individual respond verbally? Do the eyes open responsively? Is there a response when you speak the person’s name, when you ask them to squeeze your hand, if you pinch their arm? Abbreviated GCS. The scale is from 3 (the lowest) to 15 (the highest) A score of 3 is a deep coma. A score of 15 is a very light coma with a much better prognosis.

·         Gleevec   See imatinib mesylate.

·         glia   [glee´ ah]   Supportive tissue of the brain, includes astrocytes, oligodendrocytes, ependymal cells and microglia. Unlike neurons, glial cells do not conduct electrical impulses; and they can reproduce. The largest percentage of brain tumors arise from glia. Also called glial tissue, glial cells, neuroglia.

·         Gliadel   Brand name of a biodegradable polymer wafer used to deliver BCNU chemotherapy.

·         GliaSite RTS   Brand name of a balloon and catheter device used to deliver a form of interstitial radiation.

·         glioblastoma multiforme   [glee o blas toe´ ma • mul´ tee form]   A grade IV astrocytoma that commonly invades adjacent tissue and can spread widely within the brain. Its hallmark is areas of dead tumor cells (necrosis) found within the tumor. The glioblastoma multiforme represents about one-quarter of all primary brain tumors. Abbreviated GBM.

·         glioma   [glee o´ ma]   A general name for tumors that arise from the supportive tissue (called glial or neuroglial tissue) of the brain; they are a common primary brain tumor. Astrocytomas, ependymomas, oligodendrogliomas, and tumors with mixtures of two or more of these cell types are the most common gliomas.

·         gliomatosis cerebri   [glee o ma toe´ sis • ser ee´ bry]   This tumor is similar to glioblastoma multiforme, but the cells of gliomatosis cerebri are more scattered and widespread. It also lacks the necrotic center of the glioblastoma multiforme.

·         gliosarcoma   [glee o´ sar ko´ ma]   A variant of the glioblastoma multiforme tumor.

·         gliosis   [glee o´ sis]   An increase in quantity of neuroglia supportive cells of the brain.

·         glomus jugulare   [glow´ mus • jug you lair´ ee]   These usually benign, slow growing tumors are very rare. They widely invade the temporal bone and are the most common tumor of the middle ear. Glomus jugulare tumors occur most often in women in their 50s.

·         glossopharyngeal nerve   [glos´ o fa rin´ je al]   9th cranial nerve.

·         glucocorticosteroids   [glu ko kor tih ko stair´ oid]   Medications used to decrease swelling and inflammation around tumors. Commonly called “steroids.” Example: Decadron   [dek´ ah dron]   a proprietary name for Dexamethasone.

·         GM-CSF  Granulocyte-macrophage colony-stimulating factor. A substance that stimulates the production of white blood cells, especially granulocytes and macrophages.

·         grade   A number from I (one) to IV (four) that indicates a tumor’s degree of malignancy, with IV being the most malignant.

·         grading   A system for classifying tumors in terms of how  abnormal they appear when examined under a microscope. The purpose of a grading system is to provide information about the probable growth rate of the tumor and its tendency to spread. This information is used in treatment planning and facilitates communication between the various healthcare
specialists involved in the treatment.

·         grand mal seizure   A type of generalized seizure, it causes a loss of consciousness, followed by tonic (twitching) and clonic (relaxing) muscle contractions. Also called tonic-clonic seizure.

·         grant   Money given for a specific purpose, such as a research project.

·         granuloctye colony-stimulating factor   A substance that stimulates the production of blood cells, especially platelets. It is a cytokine. Abbreviated G-CSF.

·         granulocyte   [gran´ you low site]   A white blood cell filled with granules containing potent chemicals that allow the cells to digest microorganisms, such as bacteria, or to produce inflammatory reactions. Neutrophils, eosinophils and basophils are granulocytes.

·         Gray   Ionizing radiation is measured by the amount of energy the body absorbs, and the unit of measurement is the Gray (Gy) Other units include the centiGray (cGy) and the rad. One cGy equals one rad. One hundred cGy equals one Gray. For example, 60 Gy equals 6,000 cGy equals 6,000 rad. (The term “rad” is no longer used, but it is still found in the medical literature).

·         gray matter   Gray matter, the “thinking brain,” appears gray because it is composed of numerous nerve cells and blood vessels. The outer layer of the cerebrum —the cerebral cortex, and areas deep within the brain — the basal ganglia, are made up of gray matter. See white matter.

·         GRID   See SFR (Spatially Fractionated Radiation)

·         growth factor   Several naturally occurring proteins that promote cell growth by causing cell division (mitosis). They are produced by normal cells during embryonic development, tissue growth, and wound healing. Tumors, however, produce large, inappropriate amounts of growth factor. Manipulating growth factors or their receptors and the effects of doing so is the focus of much research.

·         growth hormone   Stimulates growth; produced by the pituitary gland. If deficient, can be provided by replacement therapy. Also called somatotropin.

·         GTV   Gross Tumor Volume.

·         Gy   [Gray]   Ionizing radiation is measured by the amount of energy the body absorbs, and the unit of measurement is the Gy. Others units include the centiGray (cGy) and the rad. One cGy equals one rad. One hundred cGy equals one Gy. For example, 60 Gy equals 6,000 cGy equals 6,000 rad. (The term rad is no longer used, but it is still found in the medical literature).

·         gyrus   [ji´ rus]   An interior, convoluted folding or ridge of the surface of the cerebral cortex. The precentral gyrus is a fold of the frontal lobe and the postcentral gyrus is a fold of the
parietal lobe.