148 Chapter 9 transferred from the CT scanner to the MRI system for an MRA study. Therefore, only if MRA can be shown to possess a better diagnostic performance than CTA will its use be recommended in the detection of intracranial aneurysms. Our study, described in Chapter 2, has shown no benefit of contrast enhanced MRA (CEMRA) over CTA. Proposal 3. CEMRA has no benefit over CTA in the detection of intracranial aneurysms in patients with a possible aneurysmal SAH, and CTA should be used as the primary imaging modality in these patients. CTA for treatment planning After CTA shows an aneurysm to be the cause of SAH, a treatment strategy must be selected. The goal of the treatment is to prevent a rebleed from the aneurysm in question, or a new bleed from other existing aneurysms. Since the publication of the results of the International Subarachnoid Aneurysm Trial (ISAT), endovascular coiling is the preferred treatment method.18,19 As a consequence, images acquired by any given diagnostic modality should enable assessment of endovascular coiling feasibility, or “coilability” of the aneurysm. If coiling is not possible, neurosurgical clipping is the other treatment option.3 In the majority of cases, CTA images are sufficient to assess whether an aneurysm can be coiled or not.20-25 Aneurysms considered suitable for coiling through CTA findings will later be subjected to DSA imaging at the onset of the coiling procedure. If, at this point, the aneurysm proves unsuitable for coiling, the patient can be scheduled for a surgical clipping procedure. The drawback of this approach is that the patient has undergone an unnecessary procedure under general anesthesia. Another drawback of basing the decision to treat endovascularly or not only on CTA findings is that, if an aneurysm is considered unsuitable for endovascular treatment, surgical clipping will be performed where possible; if this decision is later proved to be incorrect, and the aneurysm was in fact coilable, the preferred endovascular treatment will have been unjustly withheld. From our cost-effectiveness study (Chapter 8) it appears that the most cost-effective diagnostic strategy is to base the choice of treatment on CTA images, and to perform additional DSA only when an aneurysm is considered unsuitable for endovascular coiling. In the simulation study (Chapter 4) we further fine-tune this strategy, limiting additional DSA studies to cases thought not suitable for endovascular coiling based on CTA but with some doubt about this decision. If the neuro-interventionist is confident about his decision not to coil the aneurysm, no additional DSA is required (Fig 1). We did not test this strategy in our cost-effectiveness analyses, as it was not possible to define the level of uncertainty for the decision not to coil an aneurysm in the Markov-model. The clinical difference in outcome between this fine-tuned strategy and the strategy tested in our Markov model is that, in the cohort of 75 patients included in our simulation study, 13 patients would have undergone additional diagnostic DSA, which would have led to the transfer of one patient from the clipping group to the group assigned to a coiling procedure. Considering the minimal difference in outcome for patients that are clipped or coiled,19,26 and the existing controversies in total costs of endovascular and neurosurgical treatment,27-35 we consider it justifiable to use the following diagnostic strategy (See Box 4 and Figure 1). Proposal 4. Additional DSA is recommended only for those aneurysms appearing unsuitable for endovascular coiling based on CTA in which some doubt of this unsuitability exists.
proefschrit Van Zwam inhoud met kaft en stellingen.indd
To see the actual publication please follow the link above