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Can Noncontrast Head Computed Tomography Within 6 Hours of Symptom Onset Exclude Aneurysmal Subarachnoid Hemorrhage?
NEUROLOGY/SYSTEMATIC REVIEW SNAPSHOT
TAKE-HOME MESSAGE A normal result for noncontrast head computed tomography (CT) obtained within 6 hours of symptom onset appears to substantially decrease the likelihood of subarachnoid hemorrhage. Can Noncontrast Head Computed Tomography Within 6 Hours of Symptom Onset Exclude Aneurysmal Subarachnoid Hemorrhage?
METHODS DATA SOURCES An expert librarian was used to search MEDLINE, EMBASE, Web of Science, and Scopus from their inception. Reference lists of relevant articles and the authors’ personal collections were also searched. No language restrictions were applied. STUDY SELECTION All clinical trials of adults (>15 years) with a history concerning for spontaneous nontraumatic subarachnoid hemorrhage evaluated with noncontrast modern-generation (16 slice or greater) head CT within 6 hours of symptom onset were included. DATA EXTRACTION AND SYNTHESIS Two authors independently extracted data and assessed for risk of bias. Trial quality was scored with the Quality Assessment of Diagnostic Accuracy Studies tool. When available, data were collected to construct 22 tables. Diagnostic accuracy measures were pooled with a random-effects model to determine sensitivity, specificity, and likelihood ratios with 95% confidence intervals. Heterogeneity was reported with the I2 statistic.
Volume
-,
no.
-
:
-
2016
EBEM Commentators
Theron S. Williams, MD Rawle A. Seupaul, MD Department of Emergency Medicine University of Arkansas for Medical Sciences Little Rock, AR
Results Summary test characteristics from Perry et al.1 (95% CI), % Sensitivity Specificity Negative predictive value Positive predictive value
100 100 100 100
(97–100) (99–100) (99.5–100) (96.9–100)
CI, Confidence interval.
Of 882 titles, 5 trials (8,907 patients) were included for analysis. Four had a retrospective design and 1 was prospective. Aside from the single prospective cohort trial, overall trial quality was moderate to poor, with a high risk of bias.
Commentary Acute-onset atraumatic headache is a common emergency department (ED) presentation. Of greatest concern is the potential for subarachnoid hemorrhage, which, if missed, is devastating. Traditionally, a normal noncontrast head CT result is followed by a lumbar puncture to rule out subarachnoid hemorrhage. The rationale behind this diagnostic algorithm is that head CT alone lacks sufficient
sensitivity to exclude the disease. Unfortunately, lumbar puncture has antecedent risks. Roughly 25% to 40% of ED patients will experience a postdural-puncture headache requiring therapy,2 and 10% to 15% experience traumatic taps resulting in unnecessary vascular imaging,3 among other complications (eg, back pain, infection, spinal cord compression). This systematic review sought to determine whether head CT alone can safely exclude subarachnoid hemorrhage, given the following circumstances: “a neurologically normal patient, a thunderclap headache presentation, a clear time of onset, and a modern CT scan performed within 6 hours of onset read by an attending Annals of Emergency Medicine 1
Systematic Review Snapshot
radiologist.”4 The strength of the literature is driven by 1 large, wellexecuted, prospective cohort trial by Perry et al.1 No subarachnoid hemorrhages were missed in this trial, in which 121 of 953 patients were evaluated within 6 hours. Unfortunately, all other included trials (4) were retrospective, reporting a total of 13 missed subarachnoid hemorrhages out of the 8,907-patient sample; 11 of these misses were attributed to a single retrospective case control trial of 55 subarachnoid hemorrhages.5 Four of those 11 patients had a normal cerebral angiogram result, and 5 studies either did not specify the type of CT scanner used or were 16-slice or less. The remaining trials in this review were also retrospective, with similar weaknesses. According to this systematic review, the estimated worse-case scenario is that head CT will miss fewer than 1.5 subarachnoid hemorrhages of every 1,000 (0.15%). Considering
2 Annals of Emergency Medicine
that commonly used ED decision instruments such as the Pulmonary Embolism Rule-out Criteria rule6 and HEART (history, EKG, age, risk factors and troponin) score7 achieve miss rates of less than 2%, it may be reasonable to use this information for shared decisionmaking when evaluating the patient with suspected subarachnoid hemorrhage.8 Editor’s Note: This is a clinical synopsis, a regular feature of the Annals’ Systematic Review Snapshots (SRS) series. The source for this systematic review snapshot is: Dubosh NM, Bellolio MF, Rabinstein AA, et al. Sensitivity of early brain computed tomography to exclude aneurysmal subarachnoid hemorrhage: a systematic review and meta-analysis. Stroke. 2016;47:750-755.
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8. 1. Perry JJ, Stiell IG, Sivilotti ML, et al. High risk clinical characteristics for subarachnoid haemorrhage in patients with acute headache: prospective cohort study. BMJ. 2010;341:c5204. 2. Seupaul RA, Somerville GG, Viscusi C, et al. Prevalence of postdural puncture
headache after ED performed lumbar puncture. Am J Emerg Med. 2005;23: 913-915. Edlow JA, Caplan LR. Avoiding pitfalls in the diagnosis of subarachnoid hemorrhage. N Engl J Med. 2000;342:29-36. Dubosh NM, Bellolio MF, Rabinstein AA, et al. Sensitivity of early brain computed tomography to exclude aneurysmal subarachnoid hemorrhage: a systematic review and meta-analysis. Stroke. 2016;47: 750-755. Mark DG, Hung YY, Offerman SR, et al. Nontraumatic subarachnoid hemorrhage in the setting of negative cranial computed tomography results: external validation of a clinical and imaging prediction rule. Ann Emerg Med. 2013;62:1-10.e11. Kline JA, Courtney DM, Kabrhel C, et al. Prospective multicenter evaluation of the pulmonary embolism rule-out criteria. J Thromb Haemost. 2008;6: 772-780. Backus BE, Six AJ, Kelder JC, et al. A prospective validation of the HEART score for chest pain patients at the emergency department. Int J Cardiol. 2013;168: 2153-2158. Hess EP, Knoedler MA, Shah ND, et al. The chest pain choice decision aid: a randomized trial. Circ Cardiovasc Qual Outcomes. 2012;5:251-259.
Michael Brown, MD, MSc, and Alan Jones, MD, serve as editors of the SRS series.
Volume
-,
no.
-
:
-
2016
TAKE-HOME MESSAGE A normal result for noncontrast head computed tomography (CT) obtained within 6 hours of symptom onset appears to substantially decrease the likelihood of subarachnoid hemorrhage. Can Noncontrast Head Computed Tomography Within 6 Hours of Symptom Onset Exclude Aneurysmal Subarachnoid Hemorrhage?
METHODS DATA SOURCES An expert librarian was used to search MEDLINE, EMBASE, Web of Science, and Scopus from their inception. Reference lists of relevant articles and the authors’ personal collections were also searched. No language restrictions were applied. STUDY SELECTION All clinical trials of adults (>15 years) with a history concerning for spontaneous nontraumatic subarachnoid hemorrhage evaluated with noncontrast modern-generation (16 slice or greater) head CT within 6 hours of symptom onset were included. DATA EXTRACTION AND SYNTHESIS Two authors independently extracted data and assessed for risk of bias. Trial quality was scored with the Quality Assessment of Diagnostic Accuracy Studies tool. When available, data were collected to construct 22 tables. Diagnostic accuracy measures were pooled with a random-effects model to determine sensitivity, specificity, and likelihood ratios with 95% confidence intervals. Heterogeneity was reported with the I2 statistic.
Volume
-,
no.
-
:
-
2016
EBEM Commentators
Theron S. Williams, MD Rawle A. Seupaul, MD Department of Emergency Medicine University of Arkansas for Medical Sciences Little Rock, AR
Results Summary test characteristics from Perry et al.1 (95% CI), % Sensitivity Specificity Negative predictive value Positive predictive value
100 100 100 100
(97–100) (99–100) (99.5–100) (96.9–100)
CI, Confidence interval.
Of 882 titles, 5 trials (8,907 patients) were included for analysis. Four had a retrospective design and 1 was prospective. Aside from the single prospective cohort trial, overall trial quality was moderate to poor, with a high risk of bias.
Commentary Acute-onset atraumatic headache is a common emergency department (ED) presentation. Of greatest concern is the potential for subarachnoid hemorrhage, which, if missed, is devastating. Traditionally, a normal noncontrast head CT result is followed by a lumbar puncture to rule out subarachnoid hemorrhage. The rationale behind this diagnostic algorithm is that head CT alone lacks sufficient
sensitivity to exclude the disease. Unfortunately, lumbar puncture has antecedent risks. Roughly 25% to 40% of ED patients will experience a postdural-puncture headache requiring therapy,2 and 10% to 15% experience traumatic taps resulting in unnecessary vascular imaging,3 among other complications (eg, back pain, infection, spinal cord compression). This systematic review sought to determine whether head CT alone can safely exclude subarachnoid hemorrhage, given the following circumstances: “a neurologically normal patient, a thunderclap headache presentation, a clear time of onset, and a modern CT scan performed within 6 hours of onset read by an attending Annals of Emergency Medicine 1
Systematic Review Snapshot
radiologist.”4 The strength of the literature is driven by 1 large, wellexecuted, prospective cohort trial by Perry et al.1 No subarachnoid hemorrhages were missed in this trial, in which 121 of 953 patients were evaluated within 6 hours. Unfortunately, all other included trials (4) were retrospective, reporting a total of 13 missed subarachnoid hemorrhages out of the 8,907-patient sample; 11 of these misses were attributed to a single retrospective case control trial of 55 subarachnoid hemorrhages.5 Four of those 11 patients had a normal cerebral angiogram result, and 5 studies either did not specify the type of CT scanner used or were 16-slice or less. The remaining trials in this review were also retrospective, with similar weaknesses. According to this systematic review, the estimated worse-case scenario is that head CT will miss fewer than 1.5 subarachnoid hemorrhages of every 1,000 (0.15%). Considering
2 Annals of Emergency Medicine
that commonly used ED decision instruments such as the Pulmonary Embolism Rule-out Criteria rule6 and HEART (history, EKG, age, risk factors and troponin) score7 achieve miss rates of less than 2%, it may be reasonable to use this information for shared decisionmaking when evaluating the patient with suspected subarachnoid hemorrhage.8 Editor’s Note: This is a clinical synopsis, a regular feature of the Annals’ Systematic Review Snapshots (SRS) series. The source for this systematic review snapshot is: Dubosh NM, Bellolio MF, Rabinstein AA, et al. Sensitivity of early brain computed tomography to exclude aneurysmal subarachnoid hemorrhage: a systematic review and meta-analysis. Stroke. 2016;47:750-755.
3.
4.
5.
6.
7.
8. 1. Perry JJ, Stiell IG, Sivilotti ML, et al. High risk clinical characteristics for subarachnoid haemorrhage in patients with acute headache: prospective cohort study. BMJ. 2010;341:c5204. 2. Seupaul RA, Somerville GG, Viscusi C, et al. Prevalence of postdural puncture
headache after ED performed lumbar puncture. Am J Emerg Med. 2005;23: 913-915. Edlow JA, Caplan LR. Avoiding pitfalls in the diagnosis of subarachnoid hemorrhage. N Engl J Med. 2000;342:29-36. Dubosh NM, Bellolio MF, Rabinstein AA, et al. Sensitivity of early brain computed tomography to exclude aneurysmal subarachnoid hemorrhage: a systematic review and meta-analysis. Stroke. 2016;47: 750-755. Mark DG, Hung YY, Offerman SR, et al. Nontraumatic subarachnoid hemorrhage in the setting of negative cranial computed tomography results: external validation of a clinical and imaging prediction rule. Ann Emerg Med. 2013;62:1-10.e11. Kline JA, Courtney DM, Kabrhel C, et al. Prospective multicenter evaluation of the pulmonary embolism rule-out criteria. J Thromb Haemost. 2008;6: 772-780. Backus BE, Six AJ, Kelder JC, et al. A prospective validation of the HEART score for chest pain patients at the emergency department. Int J Cardiol. 2013;168: 2153-2158. Hess EP, Knoedler MA, Shah ND, et al. The chest pain choice decision aid: a randomized trial. Circ Cardiovasc Qual Outcomes. 2012;5:251-259.
Michael Brown, MD, MSc, and Alan Jones, MD, serve as editors of the SRS series.
Volume
-,
no.
-
:
-
2016