In reply

We are delighted to read that the ESO guidelines on management of unruptured intracranial aneurysms have attracted attention, ¹ and we thank Drs Bendszus and Möhlenbruch for drawing our attention to a systematic review of the literature that has become available after publication of the guidelines. ²

Drs Bendszus and Möhlenbruch challenge our suggestion to use flow diverting stents as a treatment option only if no other endovascular or microsurgical options are available to occlude the aneurysm at a risk lower than the expected 5-year risk of rupture and if the risk of rupture outweighs the risk of treatment with flow diverting stents. They criticise that this recommendation is based on what they describe as ‘a single small prospective study’ and ‘small exploratory study’, ³ and state that ‘in the meantime a plethora of retrospective and prospective controlled data is available demonstrating overwhelming safety and efficacy of flow diverting stents’, referring to the review mentioned above. ² Since we had not found any controlled studies in our systematic review of the literature, we read with interest the studies referenced in this systematic review. To our disappointment none of the 11 studies included in the review had a control group. Instead, there were seven retrospective and four prospective uncontrolled case series or cohorts. The review only reported on long-term radiological occlusion rates and complications (aneurysm rupture and late ischaemia) occurring beyond 1 year after treatment, but neither on initial complication rates, transient or permanent neurological deficits, nor on clinical outcome. Moreover, 9 of these 11 studies were sponsored or edited by industry or were written by authors who are stockholders of the stent under study or had other financial ties with the company of the flow diverter of interest. All in all, the studies mentioned by Drs Bendszus and Möhlenbruch do not support the title of their letter that treatment of unruptured aneurysms with flow diverting stents is safe and effective.

We have clearly stated for our recommendation on the use of flow diverting stents that the quality of evidence underlying this recommendation is ‘very low’ and that the strength of recommendation is ‘weak against intervention’. Nevertheless, it is incorrect to state that the recommendation is based on ‘a single small prospective study’ or ‘small exploratory study’. This single study is in fact a temporarily halted randomised clinical trial, ³ providing the only randomised data available. Because this trial was not completed, and it was only one trial, we based the recommendation also on an extensive systematic review and meta-analysis of the literature reporting on clinical complication rates of treatment of unruptured intracranial aneurysms. ⁴

Guidelines are based on the best available evidence at time of writing. Inevitably, and fortunately, recommendations may change over time if new evidence becomes available. Drs Bendszus and Möhlenbruch have referenced only one new study that has been published after our guidelines. Without pretending at all that we now have updated our systematic review of the literature, we could point to other new reviews that have recently been published and that again show that treatment with any stent or flow-diverting stents have a considerably higher risk of complications than endovascular coiling.^5,6

We do welcome results of well-designed studies to substantiate or refute our recommendations. A change of recommendations should however be based on a properly performed search of the literature, to avoid selective referencing, showing that new, good quality evidence has become available.

Finally, we would like to comment on the remark that our recommendation puts economic and legal pressure on the neurointerventionalist planning and performing the procedure. We do realise that a guideline can have legal implications – and rightly so. We also appreciate that the use of new devices may be beneficial for individual hospital departments. When developing guidelines, it is good to keep the economic burden of recommendations in mind, in particular if it concerns treatments (medications or devices) wherein industry has important influence and may have benefits. The scope then is however not the individual department or medical specialist, but health care costs in general. We do not see why a recommendation that is cautious about the use of flow diverting stents, which very likely are (much) more expensive than endovascular coiling or neurosurgical clipping, could have a negative impact on overall health care costs.