Introduction
Glioma refers to a brain tumour that is derived from glial cells, the supporting cells within the brain and spinal cord. They form from two different types of cells called astrocytes and oligodendrocytes, hence the alternative names for these tumours are astrocytomas and oligodendrogliomas respectively. Low grade gliomas are slow growing, and based on standard World Health Organisation classification, these tumours are typically considered as 'Grade I’ or ‘Grade II' tumours.
Four out of ten primary brain tumours are gliomas, out of which the majority are high-grade (malignant or cancerous) tumours, such as glioblastoma. Low grade (Grade II) astrocytomas and oligodendrogliomas can become high grade (Grade III or IV) over time. In general, oligodendrogliomas have better prognosis than astrocytomas.
Causes
As with glioblastoma, no definitive cause of glioma has been established. Although environmental factors such as mobile phone use, overhead power lines and some foods (particularly artificial sweetener aspartame) have been implicated, no studies have so far shown a link between such factors and glioma.
Symptoms
Symptoms of a low-grade glioma can be different, depending on which part or parts of the brain are affected. For example, if the area affected is responsible for controlling the left leg, there may be a numbness or weakness affecting that leg. Similarly, if the speech area is affected, there may be difficulties expressing or understanding speech.
However, the most common symptom of a low-grade glioma is seizure. During a seizure, patients may become unconscious, have involuntary movements, or symptoms may be slight and be accompanied by a strange smell or sensations affecting the stomach. Some people with low-grade glioma do not have any symptoms at all and the tumour is sometimes discovered during a scan for an unrelated condition.
Tests / Diagnosis
Initial tests to diagnose low-grade glioma include magnetic resonance imaging (MRI) or computed tomography (CT) scans, or both. Following these tests, further tests may involve obtaining a tissue sample, or biopsy. This normally happens as part of surgery to remove the tumour; unless the tumour is located deep in the brain or in a sensitive or eloquent area of the brain, in which case, a small needle may be used to obtain the sample instead.
Treatment
Depending on the location and size of the tumour, treatment options include:
- Observation – Further CT or MRI scans will be performed to monitor growth of low-grade gliomas.
- Surgery – Surgery may be performed to obtain a biopsy to confirm the type of tumour, to reduce the pressure (or mass effect) of the tumour on surrounding brain structures or to reduce the volume of tumour.
- Other treatments – Chemotherapy and radiotherapy may be given if there is tumour remaining after surgery, or if tumour progression occurs.
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