82 Chapter 4 In Scenario 4 only the patients in whom no aneurysm could be detected by CEMRA as well as those who had been allocated to surgery but in whom doubt remained about the best mode of treatment, would undergo DSA and all the patients allocated to coiling would go directly for coiling under general anesthesia. This would prevent another eight diagnostic DSA studies at the cost of one patient – the individual with two PCom aneurysms mentioned in Scenario 2– undergoing a procedure under general anesthesia where the non-coilable nature of the two aneurysms would be revealed. The costs of the four scenarios are summarized in Table 3. Scenario 1, in which all patients undergo only the standard of reference DSA examination, is the most expensive and invasive one. Scenario 2, in which only patients with a negative CEMRA study undergo DSA, generates the least costs, but is associated with a number of classification errors which is prohibitively high. In Scenario 3 only CEMRA findings which fail to detect an aneurysm or those which leave doubt with regard to the best treatment (clipping or coiling) are verified by DSA. This strategy leads to only a single misclassification but cost savings are not great. In Scenario 4 the role of DSA is further limited to CEMRA studies with negative findings and those in which doubt remains only in the subgroup assigned to surgical clipping. Cost savings are more substantial here, but at the price of one further misclassification. Figure 1. Patient with left middle cerebral artery aneurysm. a: Volume rendered reconstruction of CEMRA study. The observers considered this aneurysm as not suitable for coiling due to wide neck and branch arising from the neck of the aneurysm. No additional DSA was required by the observers. b: Oblique projection of DSA study. The aneurysm was considered suitable for coiling. The neck appears smaller than on CEMRA. The aneurysm was successfully coiled. With regard to the effects of misclassification the results of ISAT18 have shown a slightly but significantly better clinical outcome for patients treated by endovascular coiling compared with surgical clipping, at one year after treatment. The differences in outcome are smaller after a longer period22,23 and some authors even state that coiling and clipping should be considered as equivalent for results in the long term.24 Therefore the negative effect of a surgical clipping procedure where endovascular coiling would also have been feasible, is likely to be limited.
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