Astrocytoma

Astrocytoma

Astrocytomas are primary central nervous system tumors that arise primarily in and rarely spread away from the CNS parenchyma contained within the cranial vault. Astrocytomas "are CNS neoplasms in which the predominant cell type is derived from an immortalized astrocyte and account for roughly 75% of neuroepithelial tumors. In 1993 the World Health Organization (WHO) established a four-tiered histologic grading guideline for astrocytomas in an effort to eliminate confusion regarding diagnoses. The low grade astrocytomas (I & II) are among the least common of all reported brain tumors, less than 6%, while the highest grade (IV), also known as glioblastoma multiforme (GBM), is the most common primary CNS malignancy and second most frequent brain tumor. Despite the comparatively low incidence of astrocytomas to other human cancers, the higher grades (III & IV) represent disparate mortality rates. Median survival of GBM victims who forgo treatment is approximately 90 days, and even with aggressive surgical, radio- and chemo- therapies is only extended to about twelve months, while long term survival (at least five years) falls under 3%.

Diagnosis

A Computed Tomography (CT) or Magnetic Resonance Imaging (MRI) scan is necessary to characterize the extent of these tumors (size, location, consistency). CT will usually show distortion of third and lateral ventricles with displacement of anterior and middle cerebral arteries. Histologic analysis is necessary for grading diagnosis.

In the first stage of diagnosis the doctor will take a history of symptoms and perform a basic neurological exam, including an eye exam and tests of vision, balance, coordination and mental status. The doctor will then require a computerized tomography (CT) scan and magnetic resonance imaging (MRI) of the patient's brain. During a CT scan, x rays of the patient's brain are taken from many different directions; these are combined by a computer, producing a cross-sectional image of the brain. For an MRI, the patient relaxes in a tunnel-like instrument while the brain is subjected to changes of magnetic field. An image is produced based on the behavior of the brain's water molecules in response to the magnetic fields. A special dye may be injected into a vein before these scans to provide contrast and make tumors easier to identify.

If a tumor is found it will be necessary for a neurosurgeon to perform a biopsy on it. This simply involves the removal of a small amount of tumor tissue, which is then sent to a neuropathologist for examination and staging. The biopsy may take place before surgical removal of the tumor or the sample may be taken during surgery. Staging of the tumor sample is a method of classification that helps the doctor to determine the severity of the astrocytoma and to decide on the best treatment options. The neuropathologist stages the tumor by looking for atypical cells, the growth of new blood vessels, and for indicators of cell division called mitotic figures.

Treatment

For low grade astrocytomas, removal of the tumor will generally allow functional survival for many years. In some reports, the 5 year survival has been over 90% with well resected tumors. Indeed, broad intervention of low grade conditions is a contested matter. In particular, pilocytic astrocytomas are commonly indolent bodies that may permit normal neurologic function. However, left unattended these tumors may eventually undergo neoplastic transformation. To date, complete resection of high grade astrocytomas is impossible because of the diffuse infiltration of tumor cells into normal parenchyma. Thus, high grade astrocytomas inevitably recur after initial surgery/therapy and are usually treated similarly as the initial tumor. Despite decades of therapeutic research, curative intervention is still nonexistent for high grade astrocytomas; patient care ultimately focuses on palliative management.

References

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See also

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