A short summary by Dr Martin Wood, Neurosurgeon at Brisbane Clinical Neuroscience Centre, Mater Hospital Brisbane and Lady Cilento Children’s Hospital
There are well over one hundred different types of brain tumour that can occur. All tumours arise due to unregulated proliferation of a particular cell in the body, and most tumours are classified according to the cell from which they originate. In the brain, tumours are graded according to how ‘aggressive’ they are, using a grading scale of 1-4 (the ‘WHO’ grading scale) with grade 1 tumours being the least aggressive, and grade 4 the most aggressive. This scale generally refers to the rate of growth of the tumours, and their tendency to recur after treatment.
It can however be misleading in terms of how significant a tumour diagnosis is to a patient, and brain tumors are difficult to partition into those that are ‘benign’ versus those that are ‘malignant’, as we do in other parts of the body. For example, some grade 1 tumours may be ‘benign’ in the way they grow and do not spread, but very difficult to treat effectively due to location (eg an optic chiasm glioma, or some skull base meningiomas). On the other hand, there are some grade 4 tumours that grow very rapidly and have potential to spread, but they may often respond well to appropriate treatment, with the possibility of cure (eg medulloblastoma in children).
In general, it is considered that those tumours that are WHO grade 1-2 are considered ‘low grade’ or ‘benign’, whereas those that are grades 3 or 4 are considered ‘high grade’ or ‘malignant’. When thinking about benign brain tumours, there are those that arise within the brain (so-called ‘intrinsic’, or ‘intra-axial’ brain tumours) and those that grow from structures close to, or around the brain (called ‘extrinsic’ or ‘extra-axial’). Let’s look at a few of the more common benign tumours that can occur.
Gliomas – tumours that arise from the ‘glial’ cells that support the network of nerve cells in the brain are called gliomas. Those that are considered low-grade include some astrocytomas, oligodendrogliomas (Fig. 1) and ependymomas. They can all typically present in the same fashion, either by causing raised pressure in the brain (causing headaches or blurred vision), or by interfering with the function of the part of the brain in which they arise (which may manifest as an epileptic fit or weakness of a part of the body).
Even though these gliomas are considered ‘benign’, they can often be difficult to cure due to their location within the brain and the risk to important structures if they are removed. Sometimes they can recur despite complete removal. They do however grow at a slow rate and patients can often live for a long time with these tumours. Some low-grade glial tumours are very amenable to removal and cure, and these are more commonly seen in childhood. One example of this is a pilocytic astrocytoma (Fig. 2). If these can be removed, this usually results in a cure for the patient.
These tumours include those that arise from the brain’s coverings (meningiomas), from the nerves that come out of the brain (for example an acoustic neuroma that arises from the balance nerves), or from the pituitary gland (pituitary adenomas).
Meningiomas can present in the same way as the intra-axial tumours above, because they can grow large and put pressure on the brain (Fig. 3), or they can cause irritation of the brain surface leading to epilepsy. Often they are found by accident if they are small, when the patient has a head scan for some other reason.
Acoustic neuromas (more properly called vestibular schwannomas) typically present due to a gradual loss of hearing on the affected side, sometimes with balance problems or ringing in the ears.
Pituitary adenomas can interfere with hormone production, leading to problems either from overproduction of a particular hormone (e.g. growth hormone causing acromegaly), or to hormone deficiency. Less commonly these can present with visual problems due to compression of the optic nerves that lie above the pituitary gland.
All of these types of tumours usually require an MRI scan for diagnosis, although with acoustic neuromas the diagnosis is often suggested after an abnormal hearing test. These tumours are all usually treatable with surgery, but also sometimes with radiotherapy as an alternative treatment. Some can be simply observed if they are small and some pituitary tumours can be treated with medicines. In general, surgery to treat these types of tumour often takes some time to recover from, and there may be a need for physiotherapy to help restore physical function. Follow-up scans are usually required for a number of years to ensure that the tumours do not recur (although it would be unusual for this to occur).
The decision of whether or not to treat a particular tumour revolves around the threat to the patient from the tumour if left untreated (progressive disability or potentially a threat to life) versus the risk from surgery. Even though these tumours are benign, surgery to treat some of them can be very dangerous with a significant risk to function. This is usually due to a combination of the size of the tumour and being in a delicate location with lots of important surrounding structures. The considerations will be different for every individual patient.
Any tumour arising inside the head (benign or malignant) can cause symptoms of raised pressure. Typically these symptoms are headache, nausea and vomiting and blurred vision, which progress rather than go away with time. New onset of epileptic seizures is a potential warning sign that something is irritating the brain substance and this would usually prompt referral for a brain scan. Gradual loss of hearing on one side can suggest problems outside the brain at the back of the skull (e.g. an acoustic neuroma) and should prompt referral for a hearing test and sometimes lead to an MRI scan. Recurrent vomiting in children, especially if associated with headaches and unsteadiness on their feet, should always lead to further investigation to exclude a tumour.
There are many different types of low-grade or benign brain tumours and this article has only scratched the surface. Many present in subtle ways but are very treatable and potentially curable if detected early. Unexplained symptoms, particularly those that do not resolve over time, should always prompt consultation with your GP in the first instance.
This is an article excerpt from the BTSS (Brain Tumour Support Service) Edition 1, 2016 E-Newsletter, which can be downloaded below: