Our findings demonstrate that endovascular coiling compared with neurosurgical clipping was associated with higher incidences of good functional outcomes and lower incidences of in-hospital mortality, with no significant differences in the incidence of complications, in terms of aneurysm rebleed, delayed hydrocephalus, delayed ischemic neurological deficit and venous thromboembolism. However, more patients in the clipping group developed large infarcts requiring decompressive craniectomy. A lower age, favorable admission WFNS scores and endovascular treatment were consistently identified as independent predictors of good functional outcomes in elderly patients with aSAH, whilst the latter two factors were also independent predictors of in-hospital mortality.

Our study avoided preselection by including patients who, because of their clinical status, did not receive treatment of the ruptured aneurysm. Numerous studies have reported reasonable outcomes for elderly patients with aSAH, but older and poor-grade patients are often underrepresented in these analyses [4, 10, 11, 14, 15], as they are shown to be predictive of unfavorable outcomes and mortality [5, 12, 15, 24]. An important consideration in the controversial debate around treatment of elderly patients with poor-grade aSAH is the possibility of increasing the number of dependent patients [1,2,3]. The elderly are a heterogenous population with the hexegenarians differing clinically from the octogenarian subgroup. A consensus for an age cap for maximal aneurysm treatment remains to be achieved for aSAH. The clinical implications of this are that maximal active aneurysm treatment should be recommended to the young (aged 60–79) elderly subgroup, especially if they are alert at the time of presentation, given the likelihood of positive short term outcomes at 3 months. Indeed this is supported by Goldberg et al. who showed that despite its high initial mortality, maximal treatment of aSAH in the elderly resulted in a reasonable proportion of favorable outcomes [12]. Such a trend is also reflective of improvements in coiling technology and technical know-how which underpin the improvements in patient outcomes. This is further reinforced by an observed increase in the percentage of aSAH cases treated with coiling at our institution from 42% in 2009, to 63% in 2019, reflecting a gradual shift in treatment paradigm in favor of coiling [25]. Notwithstanding, the better patient outcomes after coiling compared with clipping could also be partly explained by the selection bias our included patients were inevitably subjected to [26]. At our institution, all aSAH patients are first considered for coiling, and only proceeds to clipping if not amendable to endovascular means. Hence, the general pool of clipped aneurysms were more complex with poorer grades at admission to begin with, predisposing to postoperative complications [17, 27]. However, these were accounted for in our regression and subgroup analyses.

However, we should note the possibility of coiling losing its advantage over conventional clipping in the long term. Our results showed that elderly aSAH patients who were treated endovascularly had superior functional outcomes compared to those treated neurosurgically in the short term at 3 months post discharge, but there was no statistical significance in outcomes between these two groups by 6 months post discharge. This could indicate the possibility of coiling and clipping yielding comparable outcomes in the long-term, beyond our 6-month follow-up period. Long-term follow-up of the ISAT trial lends some support to this view, reporting a comparable rate of dependency in the coiling and clipping groups in the long run [17, 27]. Moving forward, there is a need for larger prospective trials to shed light on current evidence on this important clinical topic [7]. With increasing evidence supporting the safety and effectiveness of maximal treatment in elderly patients with aSAH [4, 10, 12, 27,28,29], there may finally be sufficient clinical equipoise to warrant a randomized prospective trial that could help to address the question at hand [30].

Our findings contribute to addressing this gap in literature on the appropriate management of elderly patients with aSAH, as long as they are interpreted judiciously with the following limitations in mind. The limitations of our study stem from its retrospective nature. First, being a retrospective review, non-standardized documentation of medical records could have resulted in bias in the collected data. This limitation was mitigated by the relatively small proportion of patients with incomplete documentation or lost to follow-up, minimising attrition bias. In addition, application of multiple imputation preserving sample size and statistical power, demonstrated stable and robust risk estimates [21,22,23]. Secondly, the moderate sample size in our cohort limited further subgroup analyses to delineate the benefits of coiling over neurosurgical clipping. Despite additional analyses, our study may have been biased by residual confounders including baseline characteristics such as excessive alcohol consumption or sarcopenia which have been shown to be associated with poorer outcomes, especially in the elderly [31, 32]. For example, Katsuki et al. showed that temporal muscle thickness and area, as indicators of sarcopenia, would indicate premorbid mRS. Further work from us could include sarcopenia as potentially useful to decide surgical indication and to predict outcome after aneurysm treatment in the elderly [32]. Future work could also investigate for particular complications such as seizures and pneumonia. Ryttlefors demonstrated that, in the subgroup of elderly aSAH patients treated in the ISAT, frequency of epilepsy and pneumonia was greater after neurosurgical clipping than after coiling. They had attributed the greater rates of epilepsy to craniotomy, aneurysm dissection, and the use of self-retaining brain retractors and greater rates of pneumonia to prolonged artificial ventilation, and prolonged bed rest in patients who had undergone neurosurgical clipping [27]. Finally, our study was conducted using data from three tertiary institutions, with several different surgeons attending to the patients. There may have been slight differences in management despite a largely standardized protocol at our institutions. However, this is reflective of real-world practice and hence enhances the applicability of our findings to the general cohort of elderly patients with aSAH. The next phase of the study would be to follow-up to at least one year which would be especially valuable, in investigating the rate of complete aneurysmal occlusion and need for reoperation.