Headache is the perception of pain anywhere in the region of the head or neck.The brain tissue itself is not sensitive to pain because it lacks pain receptors. Rather, the pain is caused by disturbance of the pain-sensitive structures around the brain. Several areas of the head and neck have these pain-sensitive structures, which are divided in two categories: within the cranium (blood vessels, meninges, and the cranial nerves) and outside the cranium (the periosteum of the skull, muscles, nerves, arteries and veins, subcutaneous tissues, eyes, ears, sinuses and mucous membranes).
The most common types of headache are the "primary headache disorders", such tension-type headache and migraine. They have typical features; migraine, for example, tends to be pulsating in character, affecting one side of the head, associated with nausea, disabling in severity, and usually lasts between 3 hours and 3 days. Rarer primary headache disorders are trigeminal neuralgia (a shooting face pain) and cluster headache (severe pains that occur together in bouts).
"Thunderclap headache" may be the only symptom of SAH.Headache with fever may be caused by meningitis and confusion may be indicative of encephalitis.Headache that is worsened by straining or a change in position may be caused by increased pressure in the skull; this is often worse in the morning and associated with vomiting. Raised intracranial pressure may be due to brain tumors, idiopathic intracranial hypertension and occasionally cerebral venous sinus thrombosis. Headache in older people, particularly when associated with visual symptoms or jaw claudication, may indicate giant cell arteritis.Angle closure glaucoma may lead to headache, particularly around the eye, as well as visual abnormalities, nausea, vomiting and a red eye with a dilated pupil.