Headache red flags (SNOOP4) — which patients need urgent neuroimaging?

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### Evaluation of the "Thunderclap" Headache: SNOOP4 and Beyond **1. The SNOOP4 Mnemonic for Red Flags** The SNOOP4 mnemonic is a validated tool to screen for secondary headache etiologies: * **S: Systemic signs/symptoms** (fever, weight loss) or secondary risk factors (HIV, malignancy). * **N: Neurologic signs/symptoms** (confusion, focal deficits, papilledema). * **O: Onset** (Sudden, "thunderclap" — reaching peak intensity within seconds to <1 minute). * **O: Older age** of onset (typically >50 years). * **P1: Progression** (worsening in frequency or intensity). * **P2: Precipitated by** Valsalva, exercise, or position. * **P3: Papilledema.** * **P4: Pattern change** (new type of headache in a patient with a known primary disorder). **2. Rule Out Subarachnoid Hemorrhage (SAH)** The "worst headache of life" reaching peak intensity immediately (Thunderclap) is SAH until proven otherwise. * **Non-Contrast CT Head:** Extremely sensitive (near 100%) if performed within 6 hours of headache onset (the "6-hour rule"). Sensitivity drops significantly after 24 hours. * **Lumbar Puncture (LP):** If the CT is negative but the clinical suspicion remains high (especially if >6 hours from onset), an LP is mandatory. Look for **Xanthochromia** (spectrophotometry is preferred over visual inspection) and a non-clearing high RBC count across tubes. * **CT Angiography (CTA):** Often performed concurrently or after CT to identify the underlying vascular lesion (e.g., aneurysm). **3. Other Dangerous Etiologies (The "Don't Miss" List)** * **Cervical Artery Dissection:** Often presents with neck pain and potentially Horner’s syndrome. Consider in post-exercise thunderclap headache. * **Reversible Cerebral Vasoconstriction Syndrome (RCVS):** Characterized by recurrent thunderclap headaches over 1-3 weeks. Triggered by Valsalva, emotion, or certain drugs. * **Cerebral Venous Sinus Thrombosis (CVST):** Risk factors include prothrombotic states, pregnancy, and oral contraceptives. Often presents with progressive headache and signs of increased ICP. * **Pituitary Apoplexy:** Sudden headache with visual field deficits or ophthalmoplegia. * **Giant Cell Arteritis (GCA):** In patients >50; look for jaw claudication, scalp tenderness, and elevated ESR/CRP. **References:** 1. Edlow JA, et al. Clinical Policy: Critical Issues in the Evaluation and Management of Adult Patients Presenting to the Emergency Department With Acute Headache. *Ann Emerg Med*. 2019. 2. Perry JJ, et al. Clinical decision rules to rule out subarachnoid hemorrhage for acute headache. *JAMA*. 2013. 3. Schwedt TJ. Thunderclap Headache. *Continuum (Minneap Minn)*. 2015.