Lit Matters #3: Rethinking the Time of HA Onset to CT Cutoff for SAH

Modern multislice noncontrast head CT appears highly sensitive for aneurysmal subarachnoid hemorrhage beyond the classic 6-hour window, but the bedside meaning is still unsettled. The real question is not just missed blood on CT, but whether a missed SAH would change management or require neurosurgical intervention.

Modern CT for SAH Timing

• Twenty-four hour sensitivity signal: In this 10-year single-center analysis, modern multislice CT identified all aneurysmal SAH cases within 24 hours of headache onset, challenging the traditional 6-hour rule-out boundary.
• Intervention-focused miss risk: Among patients scanned within 24 hours, the clinically important signal was that no CT-missed SAH went on to require a neurosurgical procedure, a distinction worth hearing in the episode.
• Retrospective design limits: The study worked backward from known SAH cases, which raises spectrum and ascertainment concerns and makes the reassuring sensitivity estimate less ready for broad bedside adoption.
• Imputed onset uncertainty: Headache-onset time was missing in 224 of 347 cases, so the authors used best-case and worst-case imputation rather than observed timing, a major caveat for any time-based cutoff.
• Confidence interval reality: The reported 24-hour sensitivity for aneurysmal SAH carried a 95% confidence interval that did not prove perfection, which matters when the disease in question can be catastrophic or fatal.
• Technology versus implementation: Third-generation multislice scanners performed similarly across 64- and 128-slice platforms, suggesting scanner era alone is not the whole story behind safe SAH exclusion.