question: What causes Headaches - danger signs?: Problems with blood vessels and bleeding in the brain cancause as a headache. These include:  - Abnormal connection between the arteries and veins in the brain that usually forms before birth. This problem is called an arteriovenous malformation, or AVM.  - Blood flow to part of the brain stops. This is called a stroke.  - Weakening of the wall of a blood vessel that can break open and bleed into the brain. This is known as a brain aneurysm.  - Bleeding in the area between the brain and the thin tissue that covers the brain. This iscalled a subarachnoid hemorrhage   Other causes of headaches that should be checked by a doctor right awayinclude:  - Blood pressure that is very high  - Brain tumor  - Buildup of fluid inside the skull that leads to brain swelling (hydrocephalus)  - Buildup of pressure inside the skull that appears to be, but is not a tumor (pseudomotor cerebri)  - Carbon monoxide poisoning  - Infection in the brain or the tissue that surrounds the brain, as well as a brain abscess  - Swollen, inflamed arterythat supplies blood to part of the head, temple, and neck area (temporal arteritis)