Definition and Overview
Headache is one of the most common neurological symptoms seen in outpatient clinics. More than 90% of all headaches are benign primary headaches such as migraine, tension-type headache, and cluster headache, but about 2-4% are secondary headaches that require urgent treatment, such as cerebral hemorrhage, brain tumor, meningitis, and arterial dissection.
Headache red flags are clinical signs that suggest the possibility of secondary headaches, and systematic screening for them is key to preventing fatal outcomes due to delayed diagnosis.
Based on SNNOOP10
The SNNOOP10 list proposed by the European Headache Society in 2019 is a comprehensive risk signal system for secondary headache screening.
S — Systemic symptoms/signs
Headache accompanied by fever, weight loss, and night sweats suggests infection (meningitis, brain abscess), malignant tumor, or giant cell arteritis.
N — Neurological symptoms/signs
Headaches accompanied by local neurological deficits such as hemiparesis, paresthesia, visual field defects, double vision, gait disturbance, and convulsions suggest the possibility of stroke, brain tumor, or brain abscess.
N — Onset is sudden
Thunderclap headaches, which reach peak intensity within a few seconds to a minute, are the most typical symptom of subarachnoid hemorrhage. Cerebral venous sinus thrombosis, cerebral artery dissection, and reversible cerebral vasoconstriction syndrome (RCVS) can also manifest as thunderclap headache.
O — Onset after age 50 (new occurrence after age 50)
Headaches that occur for the first time after the age of 50 require evaluation as there is a high possibility of giant cell arteritis (temporal arteritis), brain tumor, or cerebrovascular disease.
O — Pattern change
If the pattern, intensity, or frequency of an existing headache changes significantly, the emergence of a secondary cause should be suspected.
P — Positional headache
A headache that gets worse when lying down suggests increased intracranial pressure (brain tumor, hydrocephalus), and a headache that gets worse when you stand up suggests low intracranial pressure syndrome (cerebrospinal fluid leak).
P — Precipitated by Valsalva
A headache that gets worse when coughing, sneezing, or defecating suggests the possibility of a posterior fossa lesion (Chiari malformation, brain tumor).
P — Papilledema
If papilledema is identified on fundus examination, it is a clear sign of increased intracranial pressure. Brain tumor, idiopathic intracranial hypertension (IIH), and cerebral venous sinus thrombosis must be differentiated.
P — Progressive headache
Headaches that gradually worsen over several days to weeks should be suspected of a space-occupying lesion such as a brain tumor, chronic subdural hematoma, or infection.
P — Pregnancy or postpartum
New headaches during pregnancy or within 6 weeks postpartum may indicate preeclampsia/eclampsia, cerebral venous sinus thrombosis, or posterior reversible leukoencephalopathy (PRES).
Major Secondary Headaches and Red Flags
Subarachnoid hemorrhage (SAH)
Thunderclap headache is the most characteristic, and is often described as “the worst headache of your life.” Approximately 12% of subarachnoid hemorrhages are missed during initial evaluation, most often due to mild hemorrhage headaches being mistaken for migraines. Non-contrast CT (sensitivity approximately 98% within 6 hours of onset) and lumbar puncture (confirmation of xanthochromia) are essential for diagnosis.
meningitis
The three symptoms of fever, headache, and neck stiffness (positive Kernig sign and Brudzinski sign) are typical. Bacterial meningitis can lead to death within hours, so immediate antibiotic administration and lumbar puncture are required when suspected.
Giant cell arteritis (GCA)
It is characterized by new-onset temporal headaches, jaw claudication, decreased vision, and elevated ESR/CRP in people over 50 years of age. If not treated, it can progress to permanent blindness, so if suspected, high-dose steroids are immediately started and a temporal artery biopsy is performed.
Cerebral venous sinus thrombosis (CVT)
Headache progresses subacutely and is accompanied by papilledema, convulsions, and focal nerve deficits. Pregnancy, use of oral contraceptives, and coagulopathy are risk factors, and diagnosis is made by MRI/MRV.
brain tumor
It is accompanied by progressive headache, early morning headache (increased intracranial pressure in the supine position), nausea/vomiting, and focal nerve deficits. Contrast-enhanced MRI is most useful for diagnosis.
Emergency Assessment Algorithm
Thunderclap headache approach
1. Non-contrast head CT (sensitivity approximately 98% when performed within 6 hours of onset) 2. If CT is normal, lumbar puncture (check for xanthochromia) 3. If both tests are normal, CT/MR angiography is used to differentiate RCVS, arterial dissection, etc.
Headache accompanied by focal nerve deficit
1. Brain CT or MRI (differentiating acute stroke, tumor, or abscess) 2. CT/MR angiography (differentiating arterial dissection and cerebral venous sinus thrombosis)
Fever + headache + neck stiffness
1. Immediate empirical antibiotic administration after blood culture 2. Lumbar puncture (cerebrospinal fluid analysis) 3. Brain CT (if necessary to rule out elevated intracranial pressure before lumbar puncture)
Clinical implications
Headaches with even one red flag should be approached as “secondary headaches until proven.” Conversely, if it is a typical primary headache presentation and there are no red flags, unnecessary testing can be avoided, reducing patient anxiety and healthcare costs.
It is also important to educate patients about danger signs. In particular, patients with existing headaches should be instructed to immediately visit a medical institution when they experience a headache that is “different from usual.”