Astrocytoma

Astrocytes are intimately related to the neurons of the brain. They act as a scaffold upon which the neurons and their processes are arranged. They are involved in guiding the growth of neurons during development. They may also be involved the regulation of ionic fluxes in the microscopic environs immediately surrounding the neurons. Neurons of course, are the basic cellular elements of the brain. Their concerted actions control the entire body.

Two types of astrocytes have been identified: protoplasmic and fibrous. The concentrations of either differ with respect to the geographic location within the brain. Protoplasmic being found in grey matter( the location of neuron cell bodies), and fibrous types more common in white matter(made up of the processes of neurons).

Basically there are two types of these tumours: benign and malignant. The most common type to occur in adults are the aggressively-growing or malignant type: glioblastoma multiforme and anaplastic astrocytoma. Adolescents and younger children are more likely to have low grade astrocytomas.

Benign or low grade astrocytomas are typically slow growing. Infiltration of adjacent normal brain is very common. Typical locations in children and adolescents include the cerebellum, visual pathways, and other central locations. Sometimes the tumour presents as a discrete nodule in the wall of a fluid-filled cyst. The pressure exerted on the brain by this enlarging sac, which is actually fluid secreted by the tumour, causes an increase in the pressure within the head. This may manifest as headaches or nausea and vomiting. Centrally located tumour may also announce themselves in this way. Tumours located in the visual pathways may cause a change in vision or possibly bulging of one eye more than the other.

Surgery has been proven to be curative if the resection is complete. Sometimes the effects of the surgical procedure are enough to cause a halt in the growth of the tumour. If there are significant amounts of residual tumour left after an operation, supplemental radiation may be necessary. Remnants of tumour may be left behind in some instances because a complete removal of the tumour would entail an unacceptable side effect such as blindness or paralysis. Determination of the growth characteristics of the tumour specimen can be performed to assess for the need for radiation after surgery. If the growth potential of the tumour is low, a wait and see attitude may be adopted. This is undertaken especially in younger children so that the ill effects of the radiation treatments may be delayed until the brain has reached its full potential. If the tumour shows more aggressive characteristics, then radiation therapy is the standard fare after surgery. Conventional radiation delivery techniques are usually employed. Radiosurgical uses in this field are still under investigation. Long-term survival for these patients depends on the completeness of surgery. The prognosis for the faster growing types of low grade astrocytomas is unfavorable but certainly longer than their malignant brethren.

The most common brain tumour in adults arising from within the brain itself is the glioblastoma multiforme. A very aggressively growing and relatively radiation-resistant tumour, infiltration of surrounding brain tissue is the rule. The best chances for survival lie in the patients' age and functional status prior to surgery. An age greater than 65 years and the inability to function independently portend a swift demise. The best treatment consists of surgery combined with radiation. No surgery has been proven to be curative. The estimated survival for patients with anaplastic astrocytomas is maybe two years. Patients with glioblastomas survive from upwards of 6-9 months. Promising results with regard to extending survival have been reported with delivery of a boost of radiation to the operative bed. This involves the use of brachytherapy or radiosurgery. Brachytherapy involves the temporary implantation of radioactive seeds in the brain adjacent to the previously located tumour(brachy means short). Radiosurgery delivers an additional boost of radiation through the use of x-rays or gamma rays, obviating the need for another open surgery. Reoperation for removal of dead, irradiated brain tissue may be necessary at a later date because of local swelling effects. Only a select group of patients may benefit from this additional therapy.

May 8, 1996

feanor@magicnet.net

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