Glioma
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A glioma is a type of primary central nervous system (CNS) tumor that arises from glial cells. The most common site of involvement of a glioma is the brain, but they can also affect the spinal cord, or any other part of the CNS, such as the optic nerves.
Gliomas are named according to the specific type of cell they derive from. The three main types of gliomas are astrocytomas, oligodendrogliomas, and ependymomas, which are named for astrocytes, oligodendrocytes, and ependymal cells, respectively. Mixed gliomas, such as oligoastrocytomas, contain cells from different types of glia.
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Classification
Gliomas are further categorized according to their grade, which is determined by pathologic evaluation of the tumor. Low grade gliomas are well-differentiated, slower growing, biologically less aggressive, and portend a better prognosis for the patient. High grade gliomas are undifferentiated or anaplastic, fast growing and can invade adjacent tissues, and carry a worse prognosis. There are numerous grading systems, but the most commonly used system is the World Health Organization (or WHO) grading system for astrocytomas. The WHO system assigns astrocytomas a grade from 1 to 4, with 1 being the least aggressive and 4 being the most aggressive. Various types of astrocytomas are given corresponding WHO grades.
- WHO grading system for astrocytomas
- WHO Grade 1 — e.g. pilocytic astrocytoma
- WHO Grade 2 — e.g. diffuse astrocytoma
- WHO Grade 3 — e.g. anaplastic (malignant) astrocytoma
- WHO Grade 4 — glioblastoma multiforme (most common glioma in adults)
The prognosis is worst for Grade-4 gliomas, with an average survival time of 14-18 months. Overall, the five year survival rate is 5%.
The gliomas can also be roughly classified according to their location:
- infratentorial : mostly in children (70%)
- supratentorial : mostly in adults (70%)
Symptoms
Symptoms of gliomas depend on which part of the central nervous system is affected. A brain glioma can cause headaches, nausea and vomiting, and cranial nerve disorders as a result of increased intracranial pressure. A glioma of the optic nerve can cause visual loss. Spinal cord gliomas can cause pain, weakness or numbness in the extremities. Gliomas do not metastasize by the bloodstream, but they can spread via the cerebrospinal fluid and cause "drop metastases" to the spinal cord.
Pathology
High grade gliomas are highly vascular tumors and have a tendency to infiltrate. They have extensive areas of necrosis and hypoxia. Often tumor growth causes a breakdown of the blood-brain barrier in the vicinity of the tumor. As a rule, high grade gliomas almost always grow back even after complete surgical excision.
On the other hand, low grade gliomas grow slowly, often over many years, and can be followed without treatment unless they grow and cause symptoms.
Treatment
Treatment for brain gliomas depends on the location and the grade. Often, treatment is a combined approach, using surgery, radiation therapy, and chemotherapy. The radiation therapy is in the form of external beam radiation or the stereotactic approach using radiosurgery. Spinal cord tumors can be treated by surgery and radiation. Gene therapy using lytic viruses or prodrug converting retroviruses and adenoviruses is another new development for the treatment of gliomas. Temozolomide is a chemotherapeutic drug that is able to cross the blood-brain barrier effectively and is being used in therapy. Template:Unreferenced