Letter: Superiority of Endovascular Coiling Over Surgical Clipping for Clinical Outcomes at Discharge in Patients With Poor-grade Subarachnoid Hemorrhage: A Registry Study in Japan

To the Editor: We read with great interest the article by Ishikawa et al, titled “Superiority of Endovascular Coiling Over Surgical Clipping for Clinical Outcomes at Discharge in Patients With Poor-Grade Subarachnoid Hemorrhage: A Registry Study in Japan,”1 in which the authors analyzed data from 9 high-volume cerebrovascular centers and concluded that endovascular coiling (EC) was associated with fewer poor outcomes compared with surgical clipping (SC) in patients with poor-grade subarachnoid hemorrhage. The authors reported that although in-hospital mortality was lower in the SC group in the unmatched data, this difference disappeared after propensity score matching (PSM), whereas the EC group showed better functional outcomes at discharge. However, we would like to raise some concerns about the interpretation of these results. In high-volume centers, treatment decisions are typically made on a case-by-case basis. The authors acknowledge that patients requiring urgent cerebrospinal fluid drainage or decompressive craniectomy may have been preferentially assigned to the SC group. From a clinical standpoint, such patients are likely to have significantly elevated intracranial pressure or imminent herniation and are, therefore, at intrinsically higher risk of unfavorable outcomes—irrespective of the treatment modality. Conversely, patients selected for EC are often those in whom intracranial pressure is still manageable. This intrinsic difference in baseline severity is difficult to fully adjust for using PSM. Interestingly, in the unmatched analysis, in-hospital mortality was higher in the EC group. This finding should not be overlooked, as it may reflect early deaths due to failed intracranial pressure control in patients treated with EC. Regarding the PSM analysis itself, we agree that it is a powerful tool that mimics randomization by balancing observable covariates. However, in this study, treatment decisions were not random but likely influenced by institution-specific or physician-specific preferences and experience. Thus, the matched cohort effectively consists of patients for whom either SC or EC could be considered acceptable—cases where treatment decisions might vary between institutions or even between physicians within the same center. Therefore, the results of the PSM analysis reflect a narrow subset of patients for whom both SC and EC are deemed technically and clinically feasible. In this subset—where urgent surgical decompression was not required—EC may have demonstrated better functional outcomes. However, this should not be interpreted as evidence of general superiority of EC over SC in all poor-grade subarachnoid hemorrhage cases. We also note the authors' suggestion that recent improvements in endovascular devices may explain the better outcomes in the EC group. An alternative interpretation is that the improved ability of clinicians to select appropriate patients for each treatment modality has led to a narrower subgroup in which EC seems favorable. Importantly, patients who require urgent surgical intervention, such as decompression, should still be treated accordingly, and the findings of this study should not be extrapolated to those cases. In conclusion, although the authors present valuable registry data, we believe that the interpretation of PSM findings should be made with caution, especially given the potential for residual confounding related to patient selection and institutional practice patterns.