“Sensitivity of Early Brain Computed Tomography to Exclude Aneurysmal Subarachnoid Hemorrhage: A Systematic Review and Meta-Analysis”
This article aimed to answer the question: How sensitive is a CT head performed within 6 hours of symptom onset in a patient whom there is concern for spontaneous SAH and who is neurologically intact?
A little background: Headaches are an exceptionally common chief complaint in the ED, accounting for ~2% of all annual visits. As emergent-ologists, we are tasked with the job of trying to determine who has a severe, life threatening or maiming disorder. The differential for emergent etiologies of headache is long and…headache inducing. These include meningitis, SAH, GCA, trauma, CO poisoning, pre-eclampsia, etc etc etc. SAH presents a particular challenge in how we work up these patients. Currently, ACEP guidelines recommend LP following negative CT head in ALL patients, regardless of when symptoms began. However, these guidelines haven’t been revised since 2008, and there has been a growing body of evidence in favor of avoiding unnecessary LP if possible.
SAH symptoms and risk factors: sudden onset, “thunderclap” headache, rapidly reaches maximum intensity, family or personal history of aneurysm, renal disease, connective tissue disorders, tobacco, and cocaine use.
This was a systematic review and meta-analysis where two researchers independently screened articles so as not to exclude an article that should have actually been included. Their search focused on adult patients suspected of having a spontaneous SAH who had a non-contast CT scan performed within 6 hours of symptom onset. Studies excluded from the review included: traumatic SAH, patients younger than 15 years old, older generation CT scanners, and nonhuman studies. Ultimately, 5 studies were included in the review (n= 8907).
This study determined a sensitivity of 98.7% and specificity of 99.9% for non-contrast CT head performed within 6 hours of symptom onset for a patient suspected of having a spontaneous SAH. There were 13 “missed” diagnoses, 11 of which were from a single study, 7 of these patients in whom it was unclear if it was an actual SAH or a vascular anomaly of undetermined clinical significance.
In recent years, there has been a growing body of evidence in support for stopping work-up after a negative non-contrast CT scan in patients presenting within 6 hours of symptom onset suspected of having a spontaneous SAH. It is important to consider your pre-test probability here, if the patient is well appearing with no neurological deficits it may be reasonable to avoid LP in these patients. This study did have some weakness, including excluding older generation CT scanners (who actually knows what generation CT scanner is in their department???) and images were primarily read by attending radiologist (which is not always the case on overnight shifts in academic institutions, where a scan might be read by a resident and an attending over-read may not be available until the next morning).
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;47(3):750-755. doi:10.1161/STROKEAHA.115.011386