INTRODUCTION: Recent studies have documented the high sensitivity of CT angiography (CTA) in detecting a ruptured aneurysm in the presence of acute subarachnoid hemorrhage (SAH). The practice of digital subtraction angiography (DSA) when CTA does not reveal an aneurysm has thus been called into question. We examined the efficacy of DSA in CTA negative SAH when balanced with the costs and risks associated with the procedure. METHODS: A decision tree was created using TreeAge Pro Suite 2012; in one arm a CTA negative SAH was followed-up with DSA, in the other arm patients were observed without further imaging. Based on literature review, costs and utilities were assigned to each potential outcome. Base case and sensitivity analysis were performed to determine the cost effectiveness of each strategy. A Monte Carlo simulation was then conducted, by sampling each variable over a plausible distribution, to evaluate the robustness of the model. RESULTS: Using a negative predictive value (NPV) of 95.7% for CTA, observation was found to be the most cost effective strategy ($2031.37/QALY vs $4185.88/QALY), in the base case analysis. One-way sensitivity analysis demonstrated that DSA became the more cost-effective option if the NPV of CTA fell below 92.6%. The Monte Carlo simulation produced an incremental cost-effectiveness ratio of $86 985/QALY. At the conventional willingness to pay threshold of $50 000/QALY, observation was the more cost effective strategy in 91.6% of simulations. CONCLUSION: The results of this analysis support observation as the more cost-effective clinical strategy when a CTA negative SAH is encountered in the majority of real world scenarios. Patients need not be subjected to the costs and risks associated with conventional angiography given the high sensitivity of modern CTA. DSA should be reserved only for patients exhibiting a clinical exam incongruent with perimesencephalic SAH. Copyright (C) by the Congress of Neurological Surgeons
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