Time-Dependent Test Characteristics of Head Computed Tomography in Patients Suspected of Nontraumatic Subarachnoid Hemorrhage

Abstract

Background and Purpose-A recent study suggested that in patients with acute headache suspicious of nontraumatic subarachnoid hemorrhage (SAH), cerebrospinal fluid (CSF) analysis is not needed to rule out SAH if head CT performed Յ6 hours after ictus is negative. Before implementation in daily practice, these results need replication. Therefore, we investigated test characteristics of head CT in patients with a clinical suspicion of SAH. Methods-Patients suspicious of SAH and a normal level of consciousness presenting to our tertiary care hospital between 2005 and 2012 were included. All patients had a head CT interpreted by experienced neuroradiologists and CSF spectrophotometry if head CT was negative or inconclusive. We determined test characteristics with 95% confidence intervals (CI) for nontraumatic SAH of head CT performed Յ6 or Ͼ6 hours after onset of headache. Results-Sensitivity of head CT Յ6 hours after ictus (nϭ137) was 98.5% (95% CI, 92.1%-100%), diagnosing all patients with aneurysmal and perimesencephalic SAH, but not with a cervical arteriovenous malformation. Sensitivity of head CT performed Ͼ6 hours after ictus (nϭ113) was 90.0% (95% CI, 76.3-97.2). After exclusion of patients with an atypical presentation without headache, sensitivity, specificity, negative predictive value, and positive predictive value of head CT Յ6 hours were all 100%. Conclusions-In patients presenting with acute headache and a normal head CT Յ6 hours after ictus, as interpreted by experienced neuroradiologists, there is no added value of CSF analysis. In patients with an atypical presentation without headache and in patients presenting Ͼ6 hours after ictus, CSF analysis is still indicated. (Stroke. 2012;43:2115-2119.)

Sensitivity of Early Brain Computed Tomography to Exclude Aneurysmal Subarachnoid Hemorrhage

“…Four had retrospective design 13,18,20,29 and one was prospective. 11 We estimated that Table I in the online-only Data Supplement.…”

“…The sensitivity decreases as time from onset to CT elapses because the blood is progressively diluted by the normal flow of cerebrospinal fluid. 6,[11][12][13][14][15][16] Recent data suggest that in neurologically intact patients, the sensitivity of modern CT scanners for SAH approaches 100% when performed within 6 hours of headache onset and interpreted by qualified radiologists. 11,13,[17][18][19][20] These data suggest that in this early-presenting population, an LP is not necessary to rule out SAH and an initial negative CT can be considered a rule-out test.…”

“…The sensitivity decreases as time from onset to CT elapses because the blood is progressively diluted by the normal flow of cerebrospinal fluid. 6,[11][12][13][14][15][16] likelihood ratios (LRs) of a brain CT performed within 6 hours of headache onset using modern generation scanners in the diagnosis of spontaneous SAH.…”

Clinical Guidelines for the Emergency Department Evaluation of Subarachnoid Hemorrhage

“…The introduction of 64-slice CT scanners and improvements in imaging software have improved the sensitivity of NCCT. If done within the first 6 h of headache onset, NCCT is reported to have a sensitivity of 100% (97.0%-100.0%), specificity of 100% (99.5%-100%), negative predictive value of 100% (99.5%-100%), and positive predictive value of 100% (96.9%-100%) (20,21,23,39). NCCT alone also may be a more costeffective strategy in the diagnosis of SAH (25).…”

Double Inversion Recovery MR Sequence for the Detection of Subacute Subarachnoid Hemorrhage

“…1 CT is highly sensitive for the diagnosis of SAH at the acute stage. 2 However, clinical symptoms may be atypical and result in delayed admission. In such patients, the diagnosis of subacute SAH is important because rebleeding may occur with subsequent life-threatening intracranial hemorrhage.…”