<< An Evidence-Based Approach To Diagnosis And Management Of Subarachnoid Hemorrhage In The Emergency Department (Stroke CME)

Diagnostic Studies

The initial investigative study in patients with suspected sSAH is the noncontrast head CT.5 Although CT has great accuracy in detecting subarachnoid blood, the emergency clinician must understand its limitations, as summarized in Table 9. Most importantly, CT findings are time-dependent. There is a decrement in the identification of hemorrhage on the scan as time from symptom onset increases because blood is degraded and diluted by the continuous circulation of CSF.109 The largest prospective observational study supporting this finding used data collected during the 1980s from over 3500 patients presenting with sSAH at various times from symptom onset using second-generation scanners; CT had a 92% sensitivity on the day of aneurysm rupture and sensitivity progressively decreased to 86%, 76%, and 58% on days 1, 2, and 5 postrupture, respectively.84

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