Glioma

A glioma is a type of primary central nervous system (CNS) tumor that arises from glial cells. The most common site of involvement of gliomas is the brain, but they can also affect the spinal cord or any other part of the CNS, such as the optic nerves.

Classification

 By type of cell

 Gliomas are named according to the specific type of cell they most resemble. The main types of gliomas are:

     * ependymomas — ependymal cells

    * astrocytomas — astrocytes

    * oligodendrogliomas — oligodendrocytes

    * Mixed gliomas, such as oligoastrocytomas, contain cells from different types of glia.

By grade 

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, 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 or low-grade astrocytoma

        * WHO Grade 3 — e.g. anaplastic (malignant) astrocytoma

        * WHO Grade 4 — glioblastoma multiforme (most common glioma in adults)

 The prognosis is the worst for Grade 4 gliomas, with an average survival time of 12 months. Overall, few patients survive beyond 3 years.  

  By location

 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, seizures, 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 

  Standard therapy

 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. Temozolomide is a chemotherapeutic drug that is able to cross the blood-brain barrier effectively and is being used in therapy.

  Experimental therapies

 The use of oncolytic viruses or gene therapy using prodrug converting retroviruses and adenoviruses is being studied for the treatment of gliomas.

 A small number of low-scale clinical studies have shown possible links between prescription of Carphedon and improvement in a number of encephalopathic conditions, including lesions of cerebral blood pathways and certain types of glioma.

 American scientists are also studying the effects of Leiurus quinquestriatus scorpion (Israeli Yellow Scorpion) venom on glioma. They have successfully isolated the peptide chlorotoxin from the venom of the L. quinquestriatus scorpion by means of gel filtration chromatography. The peptide appears to target glioma-specific chloride ion channels within the cancerous glial cells of the brain, where it binds with a high affinity.

 As of 2006, additional research started within the past few years is ongoing. Some of the topics included in this research are:

     * efficiency of variations in radiotherapy procedures

    * drugs to stop the growth of tumors by preventing them to develop blood vessels

    * efficiency of combinations of different treatments

    * vaccination therapy

 Although there have been individual cases of patients receiving an experimental treatment who still showed no signs of tumor 3 years or even more after the first diagnosis, often a new treatment for GBM will already be considered successful if it significantly increases the percentage of survivors after two years.