Editorial: International Study of Unruptured Intracranial Aneurysms

In this issue, Mahaney and colleagues take another look at the patients enrolled in the International Study of Unruptured Intracranial Aneurysms (ISUIA).1 Published in full over a decade ago, with many follow-up reports since then, this prospective cohort study followed 1691 conservatively managed patients with unruptured intracranial aneurysms (UIAs) for at least 1 year, as well as 1917 surgically treated and 451 endovascularly treated patients. Figures 2 and 3 from the 2003 paper strongly suggested that, for microsurgically managed patients, age was a strong predictor of 1-year outcomes. In fact, combined morbidity and mortality, including neuropsychological deficits, was only 5% for patients less than 50 years of age, but more than 10% for those between 50 and 60 years, and 20% for those between 60 and 70 years. The rate of morbidity was greater than 30% for those older than 70 years of age. Most of the morbidity appears to have been in aneurysms larger than 12 mm, especially those in the posterior circulation. Figure 4 from that paper showed that the age effect was less of an issue with endovascular repair. In the current re-analysis of the primary data, the authors employ slightly different age cutoffs but again show that short-term outcomes appear to be better in older patients undergoing endovascular repair than microsurgical repair. While this may not appear surprising to those having read the original paper, the authors state that reports by others since have questioned whether older patients might be at greater risk for endovascular complications than younger patients. While these data would argue against this contention, the differing results might be explained by differences in technique and/or patient selection. Both factors might be expected to be operant here given how much has changed since the enrollment period of 1991–1998, in no small part as a result of the ISUIA. For those looking to this paper to justify the treatment of UIAs, the data on 1-year aneurysmand procedure-related morbidity and mortality appear to support treatment over watchful waiting as long as one avoids treating large aneurysms in those greater than 65 years of age with microsurgery. Given that direct clipping of such high-risk lesions has in many cases been replaced by improved bypass techniques or flow diversion, some might even argue that contemporary intervention is likely even more effective than the ISUIA data suggest. However, it is also possible that the widespread use of aspirin and statins has altered the natural history of UIAs, making them less dangerous than they were 20 years ago. This possibility, along with the well-documented decentralization of endovascular care together with the diminishing number of microsurgical cases available in training and practice, might lead one to a more pessimistic view of intervention. Perhaps the most balanced reading of these data focuses on the fact that patients were selected rather than randomized for ISUIA treatments, at a time when devices and skill sets were markedly different than they are today. Efforts to “match” cohorts in a post-hoc manner, as might be done in a propensity analysis, while of some utility, are unlikely to address all of the bias. While some have thus called for a prospective multicenter randomized trial to determine which of these world views is correct, it appears that an increasing number now concede that prospective national registries are more likely to identify best practices and guide improved patient selection. The National Neurosurgery Quality and Outcomes Database (N2QOD) vascular module is one such registry that should provide this type of insight in the years to come. (http://thejns.org/doi/abs/10.3171/2013.10.JNS131485)