Astrocytomas | Dr. Prem Pillay, Singapore
Astrocytomas are tumors that arise from astrocyle cells, which is part of the supportive (neuroepithelial) tisue of the brain.
These cells are named for their starlike shape. These are the most common primary CNS tumors, representing about half of brain and spinal cord tumors.
The most frequent types of astrocytma, in increasing degress of grade, are the pilocytic astrocytoma (grade I), astrocytoma (grade II). anaplastic astrocytoma (grade III.) and glioblastonia miltiforme(grade IV). If the tumor also contains oligodendrogltoma and/or ependymoma cells, it is called a mixed glioma.
Pilocytic astrocytomas and subependymal giant cell astrocytomas are grade I tumors. These non-infiltrating tumors occasionally form cysts or are enclosed in a cyst. Metastasis or a secondary malignant tumor is rare. Although they are slow-growing, these tumors can become very large. Grade I tumors are often effectively treated by surgery alone.
Radiation therapy may be given for incompletely removed tumors. If the tumor recurs, reoperation and some form of radiation are options. Pilocytic astrocytomas occur mainly in children. They are the most benign of the astrocytonias. Cerebellar astrocytomas and optic tract gliomas are often pilocytic tumors.
Grade II tumors include low-grade astrocytoma, fibrillary or protoplasmic astrocytoma and some pleomorphic xanthoastrocytonias. They are usually infiltrating tumors but grow relatively slowly.
A tumor’s location often determines its treatment. Complete surgical removal is sometimes possible for accessible tumors, although they can be locally invasive. If total surgical removal is thought to have been achieved, periodic follow-up with MRI or CT scans may be the only additional care required.
External beam whole brain radiation therapy is often used in addition to surgery (partial resection) or for inoperable low-grade astrocytomas. If necessary, Gamma Knife may be utilized as a boost to surgery and radiation where total removal of the tumor was not accomplished. European studies and our own experience has shown good results using implanted seeds of irradiation with permanent implants. Children younger than 3 years old may receive chemotherapy so that radiation or radiation seed implants can be delayed.
Again, stereotactic radiosurgery or Ganima Knife may be assessed as an alternative.
Anaplastic astrocytoma, sometimes called grade III malignant tumors, are tumors that grow more rapidly than low grade tumors and tend to invade nearby healthy tissue. They recur more frequently and more quickly than some lower grade tumors because their tendency to spread into surrounding tissue makes it difficult to completely remove them during surgery. An Anaplastic Astrocytonia can be a reoccurrence from a lower grade of an already treated astro-Cytonia tumor.
Treatment recommendations for these types of tumors are based on the tumor’s location, if the tumor has spread. how far it has spread and the patient’s general health and age. Surgery followed by conventional external beam radiation therapy is the primary treatment for accessible mid-grade astrocytomas. Boost radiation using interstitial or radiation seeds implanted directly into the tumor site has shown promising results in our experience. Chemotherapy-may be recommended after surgery and/or radiation therapy. Gamma Knife has been increasingly shown to be beneficial as a boost to conventional radiation in the control of these tumors.
BCNU, a commonly used drug, or the combination of procarbazine, CCNU and vincristine (PCV) have also shown promising results.
By definition, a glioblastoma multiforme (GBM) tumor is considered a grade IV tumor. This high-grade astrocytoma group is represented by the glioblastoma multiforme and variants. the gliosarcoma and giant cell glioblastoma. A malignant astrocytoma that contains areas of dead tumor cells (necrosis) is called a glioblastoma multiforme. GBM represents about 30 percent of all primary brain tumors and about-50 percent of the astrocytomas. It is more common in older adults and it affects more men than women. Nine percent of childhood brain tumors are glioblastomas.
Because of its aggressive nature and fast growing ability, the first symptoms are usually due to increased pressure in the brain. Headaches, seizures, memory loss and behavioral changes are the most common presenting symptoms. The first procedure for most GBMs is either surgery to remove the tumor, or a biopsy for diagnosis. Surgery alone rarely controls the GBM because of its aggressive nature whereby its cells quickly infiltrate throughout the brain. Thus, radiation therapy almost always follows surgery or biopsy to attempt to control the spread of the cells.