Neurosurgery, also known as brain surgery, treats problems in the brain and the structures around it. Access is gained by a making an opening in the cranium (skull). A flap of skull bone is removed, usually to be replaced after surgery. There are many reasons for neurosurgery, including taking a tissue sample (biopsy) of a tumour or removing it, treating bleeding (haemorrhage) or blood clots (haematomas) resulting from injuries; weaknesses in blood vessels (cerebral aneurysms); abnormal blood vessels; damage to tissues covering the brain; infections; severe nerve or facial pain; skull fractures; pressure in the brain after an injury or stroke; and some forms of seizure disorders (e.g. epilepsy). Neurosurgery is performed with general anaesthesia.