CNS tumours are generally divided into primary tumours, which develop from brain tissue cells or surrounding structures (i.e., meninges – meningiomas), and a much larger group of tumours, secondary tumours, that have spread (metastasised) and whose original tumour may be anywhere in the body (for example, in a breast, lung, kidney).
Primary brain tumours account for 1 to 2% of all malignant tumours. In the Czech Republic, brain tumours affect some 800 people each year, with the number of males being slightly higher. The incidence of this disease is more frequent in two age groups: children up to five years of age, and adults over 60 years of age.
Primary brain tumours are a highly varied group. Most commonly, they form from the cells of supportive brain tissue (neuroglia), and these tumours are called gliomas, making up over 50% of all CNS tumours. Simply put, according to certain histological markers and behaviour, gliomas are divided into those with a low level of malignancy (low-grade gliomas), and those with a high level of malignancy (high-grade gliomas).
Low-grade gliomas grow slowly, sometimes even over the course of several years. They are more common among younger age groups (20–40 years of age). The growth of these types of tumours does not have a clear-cut border from the surrounding healthy brain tissue, which is why it is difficult to remove it completely using surgery. Over the course of years, they can gradually grow in size or change into malignant gliomas.
High-grade gliomas most often originate in two different ways – either through natural development based on genetic disorders from a low-grade glioma, or directly from healthy brain tissue. Rapid, aggressive growth (weeks to months) is typical for these malignant gliomas. They most often affect people over the age of 50. The borders of these tumours are not distinct or clearly defined, which is why complete removal is not possible. Recurrence is common, as is renewed growth at the site or surrounding area after surgery.
When addressing common brain tumours, it is important to mention meningiomas, which are typically benign tumours that form from the membranous layers surrounding the brain, and are more common in women and persons over the age of 50. Other types of tumours include cranial nerve tumours (neurinomas), which are typically benign, as well as pituitary adenomas, which manifest in hormonal disorders or visual disorders (visual field defects due to pressure on the optic nerve). Predominantly paediatric tumours generally include medulloblastomas and ependymomas.
As with other tumours, the complete list of possible triggering mechanisms is not precisely mapped out for brain tumours. What is certain, however, is that heredity may play a role (about 5% of all brain tumours are genetically determined), and exposure to radioactive radiation, certain chemicals or viruses also has a negative effect.
