Understanding Brain TumoursDownload this book (pdf, 1.23 mb)
About brain tumours
A brain tumour forms when cells grow and divide in an uncontrollable way. When this occurs, the tumour takes up space within the skull and can interfere with the brain's normal activity. A tumour may cause damage by increasing pressure in the brain, by shifting the brain and causing it to push against the skull, and/or by invading and damaging nerve and healthy brain tissue.
The location of the tumour influences the types of symptoms that occur because different parts of the brain control different functions
What do 'benign' and 'malignant' mean?
Brain tumours can be benign or malignant (brain cancer).
- Benign brain tumours - not cancerous. Benign tumours can cause problems by pressing on the brain and spinal cord. Some people have surgery to remove the tumour, but if surgery isn't possible, cancer treatments such as radiotherapy may be used.
- Malignant brain tumours - cancerous. Tumours are usually named after the cell type from which they arise.
Brain cancer (malignant brain tumour) is very unlikely to spread to other parts of the body. Malignant brain tumours are identified as cancerous because of their rapid growth and their tendency to come back (recur) after surgery.
If cancerous cells move away from the original (primary) cancer and invade other organs and bones, this is called a secondary cancer or metastasis. A metastasis keeps the name of the original cancer. For example, lung cancer that has spread to the brain is still called lung cancer, even though you may be treated for symptoms caused by a malignant brain tumour.
Tumours are graded on a scale based on how quickly they are growing and their ability to invade nearby tissue. Grading is based on the tumours microscopic appearance.
- least malignant; tumours grow slowly and are localised
- relatively slow growing; can invade surrounding tissue; can recur as a higher grade tumour
Grade 1 and 2 tumours are called low-grade tumours.
- malignant tumours; actively reproduce abnormal cells which invade surrounding normal tissue; grow at a moderate rate
- reproduce abnormal cells quickly; often form new blood vessels to maintain rapid tumour growth; have areas of dead cells in their centre
Grade 3 and 4 tumours are called high-grade tumours.
Malignant tumours are usually named after the cell type from which they arise.
Astrocytomas: these types of tumours arise from astrocytes - cells that make up the supportive tissue of the brain. These cells have a star-like shape. Sometimes the location or appearance of the tumour is attached to its name. For example, a cerebellar astrocytoma is located in the cerebellum.
Oligodendrogliomas: these types of tumours arise from oligodendrocytes - cells that also make up the supportive tissue of the brain. These cells have a fried-egg shape. The most common location of this tumour type is in the cerebral hemisphere and they occur frequently in young-middle aged adults.
Ependymomas: these types of tumours arise from ependymal cells - cells that line the ventricles of the brain and spinal cord. These tumours are common in children.
Glioblastoma multiforme (GBM): these types of tumours arise from astrocytes (star-like shaped cells that support other cells). They are often located in the cerebral hemispheres of the brain, but can be found anywhere in the brain or spinal cord.
Mixed gliomas: these types of tumours contain a high proportion of more than one cell type - that is, both astrocytes and oligodendrocytes (and occasionally ependymal cells).
What causes brain tumours?
For most brain and spinal cord tumours the causes are unknown. However, the following are risk factors for malignant brain tumours:
- Prior radiation to the head
- Genetic predisposition e.g., neurofibromatosis (a disease which causes nerve tissue to grow tumours).