Diagnosis of Subarachnoid Hemorrhage
Time to Change the Guidelines?
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Although the most concerning diagnosis in patients presenting with thunderclap headache (abrupt onset of a severe unusual headache) is nontraumatic subarachnoid hemorrhage (SAH), only 8% to 12% of neurologically intact patients with thunderclap headache will have SAH; most have benign causes.1 Of those with aneurysmal SAH, 40% to 50% of patients will present neurologically intact. Therefore, diagnostic testing beyond history and physical examination is necessary. The initial test of choice is a noncontrast CT scan of the brain.
Although CT is an excellent test for SAH, its sensitivity is both a function of timing from the onset of the headache as well as severity of the hemorrhage.1 CT sensitivity is extremely high early but rapidly diminishes with time. Clinicians frequently encounter neurologically normal patients with a thunderclap headache and a negative CT scan. Even using third-generation scanners, CT by itself is insufficient to exclude SAH.2 Therefore, guidelines recommend that a lumbar puncture (LP) be performed in these patients whose CT scans are negative or nondiagnostic.3,4 Although LP is a relatively benign test, it adds time, patient discomfort, and, sometimes, diagnostic ambiguity from a traumatic tap.
Prior studies of CT sensitivity do not adequately account for the issue of timing in the earliest hours after the hemorrhage. In this issue of Stroke, Backes et al5 present data suggesting that CT scan is 100% sensitive for SAH if performed within 6 hours of the headache onset and apart from 2 caveats, the authors recommend …