weight loss) systemic disease (hiv infection, malignancy) neurologic symptoms or signs onset sudden (thunderclap headache) onset after age 40 years previous headache history (first, worst, or different headache) other red flag symptoms include: red flagpossible causesthe reason why a red flag indicates possible causesdiagnostic tests new headache after age 50temporal arteritis, mass in braintemporal arteritis is an inflammation of vessels close to the temples in older people, which decreases blood flow to the brain and causes pain. may also have tenderness in temples or jaw claudication. some brain cancers are more common in older people.erythrocyte sedimentation rate (diagnostic test for temporal arteritis), neuroimaging very sudden onset headache (thunderclap headache)brain bleed (subarachnoid hemorrhage, hemorrhage into mass lesion, vascular malformation), pituitary apoplexy, mass (especially in posterior fossa)a bleed in the brain irritates the meninges which causes pain. pituitary apoplexy (bleeding or impaired blood supply to the pituitary gland at the base of the brain) is often accompanied by double vision or visual field defects, since the pituitary gland is right next to the optic chiasm (eye nerves).neuroimaging, lumbar puncture if computed tomography is negative headaches increasing in frequency and severitymass, subdural hematoma, medication overuseas a brain mass gets larger, or a subdural hematoma (blood outside the vessels underneath the dura) it pushes more on surrounding structures causing pain. medication overuse headaches worsen with more medication taken over time.neuroimaging, drug screen new onset headache in a person with possible hiv or cancermeningitis (chronic or carcinomatous), brain abscess including toxoplasmosis, metastasispeople with hiv or cancer are immunosuppressed so are likely to get infections of the meninges or infections in the brain causing abscesses. cancer can metastasize, or travel through the blood or lymph to other sites in the body.neuroimaging, lumbar puncture if neuroimaging is negative headache with signs of total body illness (fever, stiff neck, rash)meningitis, encephalitis (inflammation of the brain tissue), lyme disease, collagen vascular diseasea stiff neck, or inability to flex the neck due to pain, indicates inflammation of the meninges. other signs of systemic illness indicates infection.neuroimaging, lumbar puncture, serology (diagnostic blood tests for infections) papilledemabrain mass, benign intracranial hypertension (pseudotumor cerebri), meningitisincreased intracranial pressure pushes on the eyes (from inside the brain) and causes papilledema.neuroimaging, lumbar puncture severe headache following head traumabrain bleeds (intracranial hemorrhage, subdural hematoma, epidural hematoma), post-traumatic headachetrauma can cause bleeding in the brain or shake the nerves, causing a post-traumatic headacheneuroimaging of brain, skull, and possibly cervical spine inability to move a limbarteriovenous malformation, collagen vascular disease, intracranial mass lesionfocal neurological signs indicate something is pushing against nerves in the brain responsible for one part of the bodyneuroimaging, blood tests for collagen vascular diseases change in personality, consciousness, or mental statuscentral nervous system infection, intracranial bleed, masschange in mental status indicates a global infection or inflammation of the brain, or a large bleed compressing the brainstem where the consciousness centers lieblood tests, lumbar puncture, neuroimaging headache triggered by cough, exertion or while engaged in sexual intercoursemass lesion, subarachnoid hemorrhagecoughing and exertion increases the intra cranial pressure, which may cause a vessel to burst, causing a subarachnoid hemorrhage. a mass lesion already increases intracranial pressure, so an additional increase in intracranial pressure from coughing etc. will cause pain.neuroimaging, lumbar puncture old headaches old headaches are usually primary headaches and are not dangerous. they are most often caused by migraines or tension headaches. migraines are often unilateral, pulsing headaches accompanied by nausea or vomiting. there may be an aura (visual symptoms, numbness or tingling) 30–60 minutes before the headache, warning the person of a headache. migraines may also not have auras. tension-type headaches usually have bilateral "bandlike" pressure on both sides of the head usually without nausea or vomiting. however, some symptoms from both headache groups may overlap. it is important to distinguish between the two because the treatments are different. the mnemonic 'pound' helps distinguish between migraines and tension-type headaches. pound stands for: pulsatile quality of headacheone-day duration (four to 72 hours)unilateral locationnausea or vomitingdisabling intensity one review article found that if 4–5 of the pound characteristics are present, a migraine is 24 times as likely a diagnosis than a tension-type headache (likelihood ratio 24). if 3 characteristics of pound are present, migraine is 3 times more likely a diagnosis than tension type headache (likelihood ratio 3). if only 2 pound characteristics are present, tension-type headaches are 60% more likely (likelihood ratio 0.41). another study found the following factors independently each increase the chance of migraine over tension-type headache: nausea, photophobia, phonophobia, exacerbation by physical activity, unilateral, throbbing quality, chocolate as a headache trigger, and cheese as a headache trigger. cluster headaches are relatively rare (1 in 1000 people) and are more common in men than women. they present with sudden onset explosive pain around one eye and are accompanied by autonomic symptoms (tearing, runny nose and red eye). temporomandibular jaw pain (chronic pain in the jaw joint), and cervicogenic headache (headache caused by pain in muscles of the neck) are also possible diagnoses. for chronic, unexplained headaches, keeping a headache diary can be useful for tracking symptoms and identifying triggers, such as association with menstrual cycle, exercise and food. while mobile electronic diaries for smartphones are becoming increasingly common, a recent review found most are developed with a lack of evidence base and scientific expertise. new headaches new headaches are more likely to be dangerous secondary headaches. they can, however, simply be the first presentation of a chronic headache syndrome, like migraine or tension-type headaches. one recommended diagnostic approach is as follows. if any urgent red flags are present such as visual loss, new seizures, new weakness, new confusion, further workup with imaging and possibly a lumbar puncture should be done (see red flags section for more details). if the headache is sudden onset (thunderclap headache), a computed tomography test to look for a brain bleed (subarachnoid hemorrhage) should be done. if the ct scan does not show a bleed, a lumbar puncture should be done to look for blood in the csf, as the ct scan can be falsely negative and subarachnoid hemorrhages can be fatal. if there are signs of infection such as fever, rash, or stiff neck, a lumbar puncture to look for meningitis should be considered. if there is jaw claudication and scalp tenderness in an older person, a temporal artery biopsy to look for temporal arteritis should be performed and immediate treatment should be started. old headaches the us headache consortium has guidelines for neuroimaging of non-acute headaches. most old, chronic headaches do not require neuroimaging. if a person has the characteristic symptoms of a migraine, neuroimaging is not needed as it is very unlikely the person has an intracranial abnormality. if the person has neurological findings, such as weakness, on exam, neuroimaging may be considered. new headaches all people who present with red flags indicating a dangerous secondary headache should receive neuroimaging. the best form of neuroimaging for these headaches is controversial. non-contrast computerized tomography (ct) scan is usually the first step in head imaging as it is readily available in emergency departments and hospitals and is cheaper than mri. non-contrast ct is best for identifying an acute head bleed. magnetic resonance imaging (mri) is best for brain tumors and problems in the posterior fossa, or back of the brain. mri is more sensitive for identifying intracranial problems, however it can pick up brain abnormalities that are not relevant to the person's headaches. the american college of radiology recommends the following imaging tests for different specific situations: clinical featuresrecommended neuroimaging test headache in immunocompromised people (cancer, hiv)mri of head with or without contrast headache in people older than 60 with suspected temporal arteritismri of head with or without contrast headache with suspected meningitisct or mri without contrast severe headache in pregnancyct or mri without contrast severe unilateral headache caused by possible dissection of carotid or arterial arteriesmri of head with or without contrast, magnetic resonance angiography or computed tomography angiography of head and neck. sudden onset headache or worst headache of lifect of head without contrast, computed tomography angiography of head and neck with contrast, magnetic resonance angiography of head and neck with and without contrast, mri of head without contrast lumbar puncture a lumbar puncture is a procedure in which cerebral spinal fluid is removed from the spine with a needle. a lumbar puncture is necessary to look for infection or blood in the spinal fluid. a lumbar puncture can also evaluate the pressure in the spinal column, which can be useful for people with idiopathic intracranial hypertension (usually young, obese women who have increased intracranial pressure), or other causes of increased intracranial pressure. in most cases, a ct scan should be done first. classification headaches are most thoroughly classified by the international headache society's international classification of headache disorders (ichd), which published the second edition in 2004. the third edition of the international headache classification was published in 2013 in a beta version ahead of the final version. this classification is accepted by the who. other classification systems exist. one of the first published attempts was in 1951. the us national institutes of health developed a classification system in 1962. ichd-2 main article: international classification of headache disorders the international classification of headache disorders (ichd) is an in-depth hierarchical classification of headaches published by the international headache society. it contains explicit (operational) diagnostic criteria for headache disorders. the first version of the classification, ichd-1, was published in 1988. the current revision, ichd-2, was published in 2004. the classification uses numeric codes. the top, one-digit diagnostic level includes 14 headache groups. the first four of these are classified as primary headaches, groups 5-12 as secondary headaches, cranial neuralgia, central and primary facial pain and other headaches for the last two groups. the ichd-2 classification defines migraines, tension-types headaches, cluster headache and other trigeminal autonomic headache as the main types of primary headaches. also, according to the same classification, stabbing headaches and headaches due to cough, exertion and sexual activity (sexual headache) are classified as primary headaches. the daily-persistent headaches along with the hypnic headache and thunderclap headaches are considered primary headaches as well. secondary headaches are classified based on their cause and not on their symptoms. according to the ichd-2 classification, the main types of secondary headaches include those that are due to head or neck trauma such as whiplash injury, intracranial hematoma, post craniotomy or other head or neck injury. headaches caused by cranial or cervical vascular disorders such as ischemic stroke and transient ischemic attack, non-traumatic intracranial hemorrhage, vascular malformations or arteritis are also defined as secondary headaches. this type of headache may also be caused by cerebral venous thrombosis or different intracranial vascular disorders. other secondary headaches are those due to intracranial disorders that are not vascular such as low or high pressure of the cerebrospinal fluid pressure, non-infectious inflammatory disease, intracranial neoplasm, epileptic seizure or other types of disorders or diseases that are intracranial but that are not associated with the vasculature of the central nervous system. ichd-2 classifies headaches that are caused by the ingestion of a certain substance or by its withdrawal as secondary headaches as well. this type of headache may result from the overuse of some medications or exposure to some substances. hiv/aids, intracranial infections and systemic infections may also cause secondary headaches. the ichd-2 system of classification includes the headaches associated with homeostasis disorders in the category of secondary headaches. this means that headaches caused by dialysis, high blood pressure, hypothyroidism, cephalalgia and even fasting are considered secondary headaches. secondary headaches, according to the same classification system, can also be due to the injury of any of the facial structures including teeth, jaws, or temporomandibular joint. headaches caused by psychiatric disorders such as somatization or psychotic disorders are also classified as secondary headaches. the ichd-2 classification puts cranial neuralgias and other types of neuralgia in a different category. according to this system, there are 19 types of neuralgias and headaches due to different central causes of facial pain. moreover, the ichd-2 includes a category that contains all the headaches that cannot be classified. although the ichd-2 is the most complete headache classification there is and it includes frequency in the diagnostic criteria of some types of headaches (primarily primary headaches), it does not specifically code frequency or severity