Extensive Definition
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
External Links
See also
astrocytoma in German: Astrozytom
astrocytoma in Dutch: Astrocytoom
astrocytoma in Portuguese:
Astrocitoma