SUBARACHNOID HEMORRHAGE DIAGNOSIS - LUMBAR PUNCTURE IS STILL NEEDED WHEN THE COMPUTED-TOMOGRAPHY SCAN IS NORMAL

Objectives: To determine the sensitivity of third-generation CT scanne rs for diagnosed nontraumatic subarachnoid hemorrhage (SAH) and to ass ess the impact of symptom duration on sensitivity. Methods: A retrospe ctive chart review was performed in a university-affiliated tertiary c are hospital with an annual ED volume of >100,000 patients. The target population was all patients who presented to the ED from January 1991 to September 1994 with symptoms suggestive of SAH and who had a final diagnosis of nontraumatic SAH based on either a positive CT scan or p ositive spinal fluid analysis. Patients referred from outside faciliti es were included if they had a CT done at the study site. All CT scans were done using third generation scanners, Official CT scan reports w ere used to categorize scans as positive or negative. Results: There w ere 140 patients identified with SAH, with a mean age of 56 years (ran ge 10-88). The sensitivity of CT in the diagnosis of nontraumatic SAH when performed at or before 12 hours of symptom duration was 100% (80/ 80), and 81.7% (49/60) after 12 hours of symptom duration (95% CI 95-1 00% and 69.5-90.4%, respectively; p < 0.0001), Eleven of the 140 patie nts had a negative CT and positive spinal fluid analysis, yielding an overall sensitivity of 92.1% (129/140). Conclusion: The sensitivity of third-generation CT scans for SAH decreases with time from the onset of symptoms. In this sample population, CT was able to detect all pati ents scanned less than or equal to 12 hours after symptom onset. Altho ugh the study demonstrated good sensitivity of CT scan reports for SAH when the scan was performed after less than or equal to 12 hours of s ymptom onset, additional real-time experience is needed to better defi ne the potential risk of a missed SAH should this population not recei ve the customary lumbar puncture examination in the setting of a negat ive CT scan.