Are brain tumours often misdiagnosed as tension headache?

Often? No.: Tumors and other intracranial types of pathologies are believed to occur about 0.18% of the time in patients who have or present to the doctor with headaches. So nowadays with imaging studies so easy to get and doctors usually erring on the side of caution we don't usually miss things like tumors in the head when someone has a headache. A good neurological examination often answers question.