The problem: A severe headache may make you worry about a brain tumor, which may make you think you need a CT scan. But that’s rarely true. Most people who seek medical help for head pain have tension headaches or migraines. Although those can be painful, your doctor should be able to diagnose the problem with a medical history and a neurological exam.
When you might need a CT scan: An imaging test might be appropriate if you have an abnormal neurological exam or your doctor can’t diagnose your headache based on your symptoms and an exam. But in most of those cases, you need an MRI, not a CT. That test, which does not expose you to radiation, better detects serious causes of headaches, such as aneurysms and tumors.
Source: Consumer Reports on Health March 2015