Explanation

A brain tumour is what forms when some of the cells in your brain stop doing their jobs properly and start to grow out of control. They start to divide and multiply - making more and more cells, until after a while, they make a lump called a tumour.

When a tumour gets too big, your brain starts to get squashed up against your skull. This can stop your brain from working properly, and then all sorts of weird things can start happening. These things are 'symptoms'. It is not known why you get most brain tumours, but lots of research is going on to try and find out why people get them.