140 Chapter 8 detection as well as costs up to € 2.000 for DSA. The test characteristics for CTA and MRA are based on our study performed with 75 patients. In literature, meta-analyses of test characteristics of CTA, as well as other studies, show higher sensitivity and specificity for CTA and MRA in detection of aneurysms and determination of treatment compared to our study.38-40 Since our data are stable in sensitivity analysis with assumption of up to 96% sensitivity and specificity for aneurysm detection and determination of treatment for CTA and MRA, we can assume that our conclusions are valid in a broad range of diagnostic performance. In the scenario model sensitivity analysis, increasing sensitivity and specificity for CTA and MRA shows even increasing preference of our imaging strategy starting with non-invasive imaging compared to only DSA. Comparing the two non-invasive imaging modalities, CTA was superior to MRA because it dominated in the basic model analysis. This was mainly due to lower sensitivity in determination of feasibility of coiling in MRA. We did not sub-specialize between size of aneurysm nor certainty of the observer which could have allowed a better differentiation in results. Our scenario model with initial CTA followed by DSA in case an aneurysm is detected but deemed not suitable for coiling, was found to be the most cost-effective imaging strategy. The cost savings to only DSA for all patients were € 41 per patient, which is marginal in comparison to overall one year’s costs. In case of suspected SAH, standard diagnostic imaging is non-contrast enhanced CT, followed by examination of CSF, obtained by lumbar puncture, if CT is negative.41 In case SAH is detected, performing an additional CTA study can be assumed to be less expensive than the cost that is used as input parameter in our model since labor costs for moving the patient can be neglected and only additional contrast application need to be accounted. We therefore can assume that the real cost advantage will most likely be higher. There are heated discussions about whether or not to always perform DSA in patient with suspected ruptured intracranial aneurysms.42-51 Our study contributes to this discussion with two important findings. First, DSA is both more effective, yielding higher QALYs, and less costly in overall costs than CTA and MRA. DSA is therefore superior to the non-invasive imaging modalities. Second, we analyzed a scenario that combines invasive and non-invasive diagnostic tests. We found the most efficient diagnostic approach overall to be a strategy starting with CTA as first examination, followed by DSA if no aneurysm is found or coiling of a detected aneurysm is not deemed feasible. This means that every patient undergoes an additional DSA unless an aneurysm has been detected and deemed suitable for endovascular coiling. In this case coiling under general anesthesia is planned without preliminary diagnostic DSA. This strategy yields the same amount of QALYs compared to DSA in all patients and results in slightly lower costs. Besides representing the most cost-effective approach overall, we believe that the strategy of combining CTA and DSA also represents the most practical approach in routine clinical practice. For patients with suspected SAH, we therefore recommend performing a non-contrast enhanced CT scan first. If a SAH is demonstrated, CTA is directly performed. When CTA shows no aneurysm, or shows an aneurysm which is not suitable for coiling, an additional DSA study should be performed.
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