Impact of Delayed Admission on Treatment Modality and Outcomes of Aneurysmal Subarachnoid Hemorrhage: A Prefecture-Wide, Multicenter Japanese Study

<b>Background/Objectives</b>: Aneurysmal subarachnoid hemorrhage (SAH) requires prompt treatment, yet hospital admission is occasionally delayed, and the optimal treatment strategy for such patients remains to be established. We aimed to investigate treatment modality, treatment timing, and outcomes in patients with SAH with respect to early versus delayed admission. <b>Methods</b>: A total of 1080 patients with SAH and a defined onset date were included in this prefecture-wide, multicenter, registry-based study. Baseline characteristics, late SAH complications (including vasospasm), and functional outcomes were compared between early and delayed admission groups at Day 4 or later (Day 0 = SAH onset). Additionally, the association of treatment choice (endovascular therapy or direct surgery) with treatment timing was analyzed in the delayed admission group. <b>Results</b>: Delayed admission was observed in 69 (6.4%) patients. The neurological status upon admission was significantly better in the delayed admission group, with more World Federation of Neurological Societies grades I-II (89.8% vs. 56.2% in the early admission group). Delayed admission was significantly associated with an increased incidence of symptomatic vasospasm by multivariable logistic regression analysis (odds ratio 2.51: 95% confidence interval 1.26-5.00, <i>p</i> = 0.009), while a significant difference in poor functional outcomes (modified Rankin scale 3-6) was not revealed. Although endovascular therapy use did not increase in the delayed admission group, the interval from admission to endovascular therapy was significantly shorter than that in the direct surgery group (0 [0-1] days vs. 1 [1-8] days: median [interquartile range], <i>p</i> = 0.007, Mann-Whitney U test). <b>Conclusions</b>: Delayed admission was a risk factor for symptomatic vasospasm; however, functional outcomes were not exacerbated. These results were obtained under the treatment strategy of multiple institutions, where the timing of endovascular therapy was earlier than that of direct surgery in patients with delayed admission.