Alexander E. Merkler, MD

Dubosh NM, Bellolio MF, Rabinstein AA, Edlow, JA. Sensitivity of Early Brain Computed Tomography to Exclude Aneurysmal Subarachnoid Hemorrhage: A Systematic Review and Meta-Analysis. Stroke. 2016

Subarachnoid hemorrhage (SAH) is the most devastating type of stroke – 50% of survivors are dead within six months and among those patients who survive, only 50% return to their previous level of functioning. For decades, classic neurology dogma has stated that in order to rule out a SAH, any patient who presents with a thunderclap headache (HA) must receive a lumbar puncture (LP) if the head CT is negative. However, recent data suggests that in neurologically intact patients, a CT is 100% sensitive to rule out SAH when performed within six hours using a modern generation CT scanner (16-slice or greater). Hence, is there is no longer a need to perform an LP after a negative head CT that is performed within six hours of HA onset?

In this manuscript, Dr. Dubosh et al perform a meta-analysis to determine the sensitivity of modern generation CT scanners to rule out SAH in patients presenting to an emergency department within six hours of thunderclap HA. The authors identified five articles that met their inclusion criteria; four were retrospective and one was prospective. In total, 8,907 patients with thunderclap HA underwent a CT within six hours.

Overall, thirteen out of the 8,907 patients had a missed SAH. The overall sensitivity of CT was 0.987 (95% CI 0.971-0.994), specificity was 0.999 (95% CI 0.993-1.0) and the likelihood ratio of a negative CT was 0.010 (95% CI 0.003-0.034). This equated to a miss rate of 1.5 per 1000 patients who present with thunderclap HA and receive a modern CT scan within six hours.

It is important to note that each of the five studies had certain limitations. For example, perimesencephalic hemorrhage1 and SAH caused by a cervical arteriovenous malformation2 were considered missed causes of SAH. In addition, in the one prospective study by Perry et al3 (in which there were no documented missed cases of SAH), an LP was not performed in every patient who presented with thunderclap HA and had a negative CT. Although there was close follow-up using telephone interviews and monitoring coroner’s records, there may have been missed cases of SAH.

Modern CT performed within 6 hours of patients presenting with thunderclap HA is an extremely sensitive tool to rule-out SAH. As with most tests, it is impossible to say that it is 100% sensitive, but it certainly approaches it. Although perhaps very few cases of SAH may be missed, clinicians must weigh this against the potential consequences of performing an LP including time, anxiety, post-LP complications, unnecessary vascular imaging (CTA, MRA, angiography) and probably most importantly subsequent ramifications such as inappropriate procedures for incidentally found vascular lesions. Of course, missing a SAH may be life threatening and can lead to significant consequences including death.


1. Blok KM, Rinkel GJ, Majoie CB, Hendrikse J, Braaksma M, Tijssen CC et al. CT within 6 hours of headache onset to rule out subarachnoid hemorrhage in nonacademic hospitals. Neurology. 2015;12:1927-193.

2. Backes D, Rinkel GJ, Kemperman H, Linn FH, Vergouwen MD. Time-dependent test characteristics of head computed tomography in patients suspected of nontraumatic subarachnoid hemorrhage. Stroke. 2012;43:2115-2119.

3. Perry JJ, Stiell IG, Sivilotti ML, Bullard MJ, Emond M, Symington C et al. Sensitivity of computed tomography performed within six hours of onset of headache for diagnosis of subarachnoid haemorrhage: prospective cohort study. BMJ. 2011;343:d4277.