Introduction: With advancement in imaging technology, there is emerging evidence claiming that early computed tomography (CT) has 100% sensitivity in detecting subarachnoid hemorrhage (SAH), negating the requirement for secondary investigation [1,2]. This is in the context of a modern generation CT scanners, and interpretation by experienced clinicians.

Methods: 609 consecutive patients referred to the West of Scotland regional neurosurgical service (population 2.7 million) with a diagnosis of SAH between August 2010 and August 2013 were studied. CT positive for SAH or CT negative, lumbar puncture (LP) positive for bilirubin were defined as confirmed SAH; those patients that were CT negative but LP inconclusive were not included in analysis, except patients that had a vascular anomaly that merited treatment. CT sensitivity was defined as the number of cases of confirmed SAH correctly diagnosed with a CT scan. We aimed to study the, sensitivity of modern CT scanners at various time periods from ictus.

Results: 609 patients with SAH were identified (61.9% were female). Average age at presentation was 54.8±13.5 (range 9-89 years). Overall, 531 out of 609 (87.2%) confirmed SAH were diagnosed by CT. 400 of 609 (65.7%) were scanned within 24 hours of ictus, of which 97.3% (389/400) were correctly diagnosed by CT, the remaining 11 were CT negative, and diagnosed by LP. CT sensitivity decreases with time (P < 0.00001), with more SAH diagnosed by LP in increasing time from ictus to CT, with only 52.9% diagnosed correctly by CT >72h from ictus.

Conclusions: Our data determined the sensitivity of modern high resolution, multidetector CT scanners in diagnosing SAH in different time interval after ictus, and is also shown to decrease with time. Despite several recent papers that proved that modern CT scanners have 100% sensitivity in detecting SAH, our data do not support abandoning LP for patients who present early after ictus.

Patient Care: This investigation paradigm ensures minimization of missed SAH.

Learning Objectives: We would like to revisit the discussion on the senstivity of CT for SAH in early presentation SAH in a 'real-life' setting.

References: [1] Sensitivity of computed tomography performed within six hours of onset of headache for diagnosis of subarachnoid haemorrhage: prospective cohort study. Perry JJ1, Stiell IG, Sivilotti ML, Bullard MJ, Emond M, Symington C, Sutherland J, Worster A, Hohl C, Lee JS, Eisenhauer MA, Mortensen M, Mackey D, Pauls M, Lesiuk H, Wells GA. BMJ. 2011 Jul 18;343:d4277. doi: 10.1136/bmj.d4277. [2] Cortnum S1, Sørensen P, Jørgensen J. Determining the sensitivity of computed tomography scanning in early detection of subarachnoid hemorrhage. Neurosurgery. 2010 May;66(5):900-2; discussion 903. doi: 10.1227/01. NEU.0000367722.66098.21.