I know these are already recorded but this brought up a question for me. The neurosurgeon said that they would spend an hour or so drilling a large hole in the skull to access a tumour, well that's all fine and well but what do they do about the fluid that's supposed to protect your brain and keep it afloat so it doesn't press against the skull too much? Would they drain it out and re-insert it after they're done? Or would they use a different fluid? And does this impose any time constraints on the operation, having reduced fluid in the skull? Thanks in advance to anyone who can answer any of these questions.,(reply>), The fluid will very slowly ooze out throughout the operation. We do what we can to minimise it and we don't generally replace it. The volumes that are drained are quite small and the brain will replenish it within half a day or so after the operation. <br><br>Draining way too much can lead to nasty headaches though.