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General Neurology

Headache Workup

Red flags, when to image, and when to tap

Most headaches are primary (migraine, tension, cluster). Red flags: sudden worst-ever, thunderclap, fever, focal deficit, papilledema, or immunosuppression. Work up before symptomatic treatment.

1.Red Flags

Thunderclap — SAH until ruled out. Worst-ever, sudden. Fever. Focal deficit, AMS, papilledema. Immunosuppression, cancer. New headache >50 y.[+]

2.Imaging

Thunderclap: NCCT (SAH). LP if CT negative and high suspicion. CTA if dissection/aneurysm. Mass, hemorrhage: CT or MRI.[+]

3.LP

OP, cells, protein, glucose, culture. Xanthochromia if SAH suspected and CT negative. HSV PCR, cryptococcal Ag, etc. as needed.[+]

Do not treat with triptans or opioid-only until SAH, meningitis, mass, and other dangerous causes are considered or ruled out.

Tap underlined terms for details · Tap [+] to expand

Frequently asked questions

What are the SNOOP4 red flags for secondary headache?

SNOOP4 is a mnemonic for red flags suggesting secondary headache: S — Systemic symptoms (fever, weight loss) or Secondary risk factors (HIV, cancer); N — Neurologic signs or symptoms (focal deficit, papilledema, altered mental status); O — Onset sudden (thunderclap, peaking in <1 minute); O — Older age at onset (>50 years suggests temporal arteritis); P — Pattern change (progressive, change from prior pattern), Positional (worse lying down → ICP), Precipitated by Valsalva (cough, exertion, sexual activity), Progressive, Pregnancy or Postpartum (cerebral venous thrombosis, PRES, RCVS). Any positive red flag warrants neuroimaging and targeted workup; thunderclap onset specifically mandates evaluation for subarachnoid hemorrhage.

When is lumbar puncture indicated after a negative CT for thunderclap headache?

Non-contrast CT performed within 6 hours of thunderclap headache onset, interpreted by an attending radiologist on a modern scanner, has approximately 100% sensitivity for aneurysmal subarachnoid hemorrhage (Perry, BMJ 2011). Beyond 6 hours, CT sensitivity drops progressively (~85% at 24 h, <50% at 1 week), and LP is required to exclude SAH in patients with continued clinical suspicion. CSF findings supporting SAH include elevated RBC count that does not clear between tubes 1 and 4, and xanthochromia on spectrophotometry (best detected 12 hours to 2 weeks after bleed). If LP is negative, consider CTA or MRA to evaluate for unruptured aneurysm, RCVS, or cervical artery dissection as alternative causes of thunderclap headache.

What imaging is preferred for suspected subarachnoid hemorrhage?

Non-contrast CT head is the first-line imaging study for suspected SAH — fast, widely available, and ~100% sensitive within 6 hours of symptom onset. If CT confirms SAH, CT angiography of the head and neck identifies the aneurysm or other vascular cause in >95% of cases and guides definitive treatment (clipping vs coiling). If CT is negative but clinical suspicion remains, LP for RBC count and xanthochromia is the standard next step beyond 6 hours from onset. MRI with FLAIR and gradient-echo sequences is useful in subacute SAH (>1 week) when CT sensitivity has dropped, and is preferred in pregnancy to limit ionizing radiation, paired with MRA for vascular evaluation. Catheter angiography remains the gold standard when CTA is negative but suspicion for aneurysm remains high.

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