Faculty Bibliography

OBJECTIVES: Prior studies examining the sensitivity of cranial computed tomography (CT) for the detection of subarachnoid hemorrhage (SAH) have used the final radiology report as the reference standard. However, optimal sensitivity may have been underestimated due to misinterpretation of reportedly normal cranial CTs. This study aims to estimate the incidence of missed CT evidence of SAH among a cohort of patients with aneurysmal SAH (aSAH). METHODS: We performed a retrospective chart review of emergency department (ED) encounters within an integrated health delivery system between January 2007 and June 2013 to identify patients diagnosed with aSAH. All initial non-contrast CTs from aSAH cases diagnosed by lumbar puncture (LP) and angiography following a reportedly normal non-contrast cranial CT (CT-negative aSAH) were then reviewed in a blinded, independent fashion by two board-certified neuroradiologists to assess for missed evidence of SAH. Reviewers rated the CT studies as having either definite evidence of SAH, probable evidence of SAH, or no evidence of SAH. Control patients who underwent a negative evaluation for aSAH based on cranial CT and LP results were also included at random in the imaging review cohort. RESULTS: A total of 452 cases of aSAH were identified; 18 (4%) were cases of CT-negative aSAH. Of these, 7 (39%) underwent cranial CT within six hours of headache onset, and 2 (11%) had their initial CTs formally interpreted by board-certified neuroradiologists. Blinded independent CT review revealed concordant agreement for either definite or probable evidence of SAH in 9 out of 18 (50%) cases overall, and in 5 of the 7 (71%) CTs performed within six hours of headache onset. Inter-rater agreement was 83% for definite SAH and 72% for either probable or definite SAH. CONCLUSIONS: CT evidence of SAH was frequently present but unrecognized according to the final radiology report in cases of presumed CT-negative aSAH. This finding may help explain some of the discordance between prior studies examining the sensitivity of cranial CT for SAH

To compare utilization of CT pulmonary angiogram (CTA) for diagnosis of pulmonary embolism (PE) in an emergency department (ED) with unstructured CT ordering to published rates of CT positivity in other EDs including those employing decision support and to identify pathways for improved utilization via collaboration with our pathology and ED colleagues. Two hundred seventeen patients over a 2.5-month time period who received a CTA for PE were reviewed with exclusion of pediatric patients and all sub-optimal, non-diagnostic, or equivocal scans; 21 were excluded leaving a sample of 196 patients. The rate of PE diagnosis and association of PE positivity with selected factors (D-dimer testing) was assessed. The percentage of cases positive for PE was 10.7 % (21/196) which is similar to the frequently published rate of 10 % in other emergency departments including settings that have studied the use of decision support. D-dimer testing was performed in 40.3 % of cases. In 29.6 % (58/196) of subjects, D-dimer was positive, 10.7 % (21/196) was negative, and 59.7 % (117/196) was not assessed. Prevalence of PE among D-dimer negative (0 %, 0/21) was lower versus positive D-dimer (12.1 %, 7/58) and unknown D-dimer patients (12.0 %, 14/117). D-dimer had 100 % (21/21) negative predictive value for the diagnosis of PE. While this suggests that D-dimer is useful to rule-out PE, due to the small number of patients with PE, the 95 % confidence intervals are wide and the post-test likelihood of PE could be as high as 14 %. The rate of CT positivity for PE in an ED with unstructured CT ordering is similar to that in other published series including as series in which decision support was used. While D-dimer had high negative predictive value, large studies are needed to confirm this high sensitivity and potentially increase its use in ruling out PE without CT and to reduce CT ordering particularly in patients with sufficiently low clinical pre-test probability of PE.