Headache: primary or secondary, and the red flags (SNOOP)
- Topic
Most headaches are migraine or tension-type, but a few hide a bleed, an infection or raised pressure. These are the warning signs to look for.
See it in 3D: Dura mater · Superficial temporal artery
What it is
Headache is primary when it is the disease itself (migraine, tension-type, cluster) and secondary when it is a symptom of something else, such as subarachnoid hemorrhage, meningitis or raised intracranial pressure. The bedside task is to find the few secondary headaches among the many primary ones. Red-flag lists such as SNOOP, extended in the literature as SNNOOP10, organize the questions; most patients without red flags need no tests.
Key facts
- Primary headaches: migraine (unilateral, pulsating, with nausea, light and sound sensitivity, sometimes aura), tension-type (bilateral, pressing, mild to moderate), cluster (short, severe, one eye, with tearing and nasal congestion).
- Onset: sudden and explosive points to vascular causes; days to weeks points to mass, infection or raised pressure; years of a stable pattern points to a primary headache.
- Site and character: where it hurts, whether it throbs or presses, and whether it is always on the same side.
- Triggers and modifiers: worse lying down or in the morning, with coughing or straining (raised pressure); worse standing (low pressure after lumbar puncture).
- Associated symptoms: fever, vomiting, visual loss, diplopia, weakness, confusion, seizures, red painful eye with halos.
- Background: cancer, HIV or immunosuppression, anticoagulants, head trauma, pregnancy, oral contraceptives, family history of migraine.
Step by step
- Check vital signs, temperature and level of consciousness first.
- Ask: 'Is this a new headache or your usual one? How fast did it reach its worst?'
- Go through the red flags in order (SNOOP), one by one, and write down each answer.
- Characterize the pain: site, quality, intensity, duration, frequency, triggers, and what relieves it.
- Ask about pain medicine use: which ones and how many days a month.
- Examine: neck stiffness, full neurologic exam, fundoscopy for papilledema, temporal arteries, eyes, sinuses, teeth and jaw.
- No red flags and a typical primary pattern: diagnose the primary headache clinically; red flags present: arrange imaging or referral.
Primary and secondary headaches: typical picture
| Type | Typical picture | Key clue |
|---|---|---|
| Migraine | Recurrent, unilateral, throbbing, hours to days | Nausea, light sensitivity, aura; family history |
| Tension-type | Bilateral, pressing band, mild to moderate | No nausea or aura; daily activity does not worsen it |
| Cluster | Severe, around one eye, under about three hours | Tearing, red eye and nasal congestion on the same side; restlessness |
| Subarachnoid hemorrhage | Sudden 'worst ever' headache | Peak within about a minute, vomiting, neck stiffness, fainting |
| Bacterial meningitis | Headache over hours with fever | Neck stiffness, confusion, rash |
| Idiopathic intracranial hypertension | Daily headache, worse lying down | Young woman with obesity, papilledema, transient visual loss |
| Giant cell arteritis | New headache after 50 | Jaw claudication, tender temporal artery, visual loss, raised ESR |
| Cerebral venous thrombosis | Progressive headache, days | Pregnancy or puerperium, contraceptives, seizures, papilledema |
Clinical notes
- Thunderclap headache needs urgent brain CT; if CT is normal and suspicion remains, lumbar puncture.
- Fever, headache and altered consciousness or rash: suspected bacterial meningitis is an emergency; treatment should not wait for imaging.
- Headache with focal deficit, confusion or papilledema needs urgent imaging.
- Painful red eye with halos and a mid-dilated pupil suggests acute angle-closure glaucoma.
- Headache in a patient with cancer or HIV: consider metastases, abscess or opportunistic infection.
- Headache after a head injury in an older or anticoagulated patient: rule out subdural hematoma.
In the lab
- Most primary headaches need no tests.
- Non-contrast brain CT for thunderclap headache or acute deficit; MRI for subacute deficit, change in pattern, cancer or HIV.
- Lumbar puncture when meningitis or subarachnoid hemorrhage with normal CT is suspected, after imaging when indicated.
- ESR and C-reactive protein when giant cell arteritis is suspected; venous imaging when venous thrombosis is suspected.
Test yourself
Think of the answer, then tap the question to see it.
What does each letter of SNOOP stand for?
Systemic symptoms or illness, Neurologic signs, Onset sudden, Older age at onset, Pattern change or progression (plus positional, Valsalva-provoked and papilledema).
Which test comes first in a thunderclap headache?
An urgent non-contrast brain CT; lumbar puncture follows if CT is normal and suspicion of hemorrhage remains.
Which features separate cluster headache from migraine?
Cluster is shorter, strictly around one eye, with same-side tearing and nasal congestion, and the patient is restless rather than lying still.
Which diagnosis must be considered in a new headache after 50 with jaw pain on chewing?
Giant cell arteritis, because it can cause sudden permanent visual loss.
Connections
See it in 3D2
The structures of Durgical's 3D anatomy where it is found.
Educational content on the clinical exam; it is learned and practised under supervision. It does not replace assessment by a health professional and is not for self-diagnosis.
Sources: Headache (MedlinePlus Medical Encyclopedia, U.S. National Library of Medicine, 2025); Approach to the Patient With Headache (MSD Manual Professional Edition, 2025); Red and orange flags for secondary headaches in clinical practice: SNNOOP10 list (Neurology (Do TP et al.), via PubMed Central, 2019).
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Representative model, for educational purposes only.