Brain Tumors

What is an astrocytoma?

An astrocytoma is a brain tumor made up of astrocytes. An astrocyte is one type of brain glial cell. Glial cells are the most numerous cells in the brain. Their major function is to provide support, both physical and nutritional to the information carrying cells of the brain, the neurons. Abnormally multiplying astrocytes which form a mass within the brain are an astrocytoma. Astrocytomas, even the most aggressive, do not metastasize through the blood and lymphatic systems. In this sense they differ from cancers that arise in other organs of the body. Although astrocytomas can behave in a "malignant" manner they should really be differentiated from true cancers that occur elsewhere in the body because these brain glial tumors do not metastasize.

Among astrocytomas there are more and less aggressive types. The most aggressive astrocytoma is called glioblastoma multiforme, the next moderately aggressive type of astrocytoma is anaplastic astrocytoma and the least aggressive and most benign behaving is simply called astrocytoma. In addition to these three major categories of astrocytoma other special types each of which has a slightly different prognosis. Pilocytic astrocytomas are tumors primarily of children and have a very good prognosis after removal with no further treatment.

Although they do not metastasize like malignant cancers, astrocytomas are not "benign" because they grow locally within the brain increasing in volume until they begin to press on parts of the brain important for such functions as breathing, moving, feeling, thinking and consciousness. Astrocytomas spread by infiltration. Cells from the tumor move into and mix themselves among normal brain cells. With the naked eye, or even under an operating microscope (which only magnifies approximately five times) normal brain tissue and tissue infiltrated by tumor cells appears the same. It is only with the neuropathologists high-power microscope magnifying 25 to 40 times that abnormal tumor cells can be seen as they mix in with normal brain tissue. It is not possible even with a surgical microscope to completely resect an infiltrative astrocytoma. This means that astrocytomas are not surgically curable. Astrocytomas are the most common type of tumor in the brain that arises from brain tissue. There are approximately 12,000 new cases of astrocytoma every year.

What causes astrocytomas?

The cause of an astrocytoma is unknown. There are no known environmental or behavioral risk factors (such as air pollution or smoking). There may be a genetic abnormality although there is no evidence that astrocytomas are hereditary in families.

What are the symptoms of an astrocytoma?

The first symptom of a brain tumor of any type can be a headache. The reason that patients get headaches with brain tumors is that these masses cause increased pressure in the brain. The headache associated with a brain tumor is frequently worse in the morning and is characterized by vomiting without nausea. Other symptoms of a brain tumor can include seizures (also called epilepsy), weakness or numbness of a side or part of the body, or even such subtle symptoms such as changes in mood, thinking or general state of well-being. Sometimes increased pressure in the brain can cause blurred, double or lost vision.

What do I do if I have these symptoms?

If a patient has any of the symptoms mentioned above with no other obvious explanation a diagnostic work-up should be done. Astrocytoma, like other brain tumors, is currently best seen on magnetic resonance imaging (MRI) studies of the head which give good pictures of the brain and its anatomy, both normal and abnormal. Computerized tomography (CT) is also a good technique for seeing structures in the head and brain but does not show quite as much detail as does MRI. The problem with MRI is that while it is a good technique for detecting a brain mass, it does not identify the type of mass. An astrocytoma can look like other kinds of brain tumor, or even like an infection. A biopsy is needed to confirm the diagnosis of astrocytoma and also to grade the tumor in order to select appropriate treatment and predict survival time. The microscopic structure of an astrocytoma is extremely important in making decisions about treatment and in predicting survival. Neuropathologists who analyze the microscopic structure of brain tumors have come up with several grading schemes which correlate microscopic structure to prognosis. On the basis of features of cells within tumors, neuropathologists can predict how aggressively a tumor will behave, which ultimately determines how long a patient will survive and in what condition.

What is the treatment?

The treatment of an astrocytoma can be surgical or non-surgical. The primary non-surgical treatment is radiation. Radiation can be administered to the whole brain or it can be relatively focused to a region of the brain. A new technology called Gamma Knife and a variant of this called radiosurgery allow very precise focusing of radiation beams into the area of astrocytoma involvement without doing damage to surrounding brain. Unfortunately the energy from radiation is destructive to normal brain cells as well as abnormal tumor cells although less so. Radiation therapy causes damage to the brain which can be temporary in the form of temporary swelling or permanent with death of brain cells.

Chemotherapy is another option for treatment of brain tumors, but the results of chemotherapy whether the agent is an extremely toxic systemic poison, such as BCNU or one of the less toxic agents currently under investigation such as tamoxifen or hypericin, are not very good in terms of arresting the growth of aggressive astrocytomas.

New therapies such as gene therapy will be required to treat astrocytoma. Because of the infiltrative nature of astrocytoma it does not appear that surgery will ever be the definitive treatment for these neoplasms.