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Clinical Controversies: SAH

Blake Briggs, MD and Matthew DeLaney, MD, FACEP, FAAEM

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The summary below is from an episode of ERcast: Clinical Perspectives

Subarachnoid hemorrhage is the headache diagnosis emergency clinicians most fear missing, but the real controversy is what to do after a negative noncontrast head CT. Ottawa SAH Rule use, the 6-hour CT rule, and the LP-versus-CTA decision all hinge on strict inclusion criteria and a realistic view of downstream harms.

Subarachnoid Hemorrhage Workup Nuances

  • Thunderclap headache signal: Sudden severe headache reaching maximal intensity within 1 minute is the strongest historical clue, with about 97% sensitivity, while nausea, vomiting, or unilateral pain are far less discriminating.
  • Ottawa SAH Rule limits: The Ottawa SAH Rule is 100% sensitive only when every inclusion and exclusion is respected; its specificity is poor at roughly 8% to 15%, so many patients still trigger imaging. We walk through the practical fit in the episode.
  • Six-hour CT rule: A modern noncontrast head CT read by an experienced radiologist can reduce the miss rate for aneurysmal SAH to under 1% when obtained within 6 hours in a neurologically intact patient.
  • Critical CT caveats: The early-CT strategy depends on more than timing alone: normal mental status, no focal deficits, a modern scanner, typical presentation, and no significant anemia all matter.
  • LP interpretation pitfalls: Lumbar puncture is highly sensitive for subarachnoid blood, but traumatic taps muddy the picture and tube-to-tube RBC clearing has not proven reliable for separating artifact from true SAH.
  • CTA versus LP tradeoff: CTA is highly accurate for aneurysms larger than 3 mm and avoids a painful procedure, but incidental aneurysms, radiation, and cost shift the conversation toward shared decision-making after a negative CT.

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References:

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  7. Probst MA, Hoffman JR. Computed Tomography Angiography of the Head Is a Reasonable Next Test After a Negative Noncontrast Head Computed Tomography Result in the Emergency Department Evaluation of Subarachnoid Hemorrhage. Ann Emerg Med. 2016;67(6):773-774. PMID: 27217126
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  12. Wiebers DO, et al. Unruptured intracranial aneurysms: natural history, clinical outcome, and risks of surgical and endovascular treatment. Lancet. 2003;362(9378):103-110. PMID:12867109
  13. Czuczman AD, et al. Interpreting red blood cells in lumbar puncture: distinguishing true subarachnoid hemorrhage from traumatic tap. Acad Emerg Med. 2013;20(3):247-256. PMID: 23517256

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