In-Transit Deterioration and Hydrocephalus Development During Interhospital Transfer in Aneurysmal Subarachnoid Hemorrhage

BACKGROUND AND OBJECTIVES: Most patients with aneurysmal subarachnoid hemorrhage (aSAH) initially present to local/low-volume facilities and require interhospital transfer (IHT) for neurovascular care. We aimed to evaluate the transfer interval as a vulnerable phase in aSAH care, focusing on in-transit neurological and radiological changes, hydrocephalus development, and process delays. METHODS: This retrospective cohort study included adults with aSAH treated at our tertiary care center between 2010 and 2023. Patients were categorized as direct admissions or IHT. Among IHT patients, neurological status and neuroimaging were compared between the referring hospital and the tertiary center on arrival. Missing paired imaging was addressed using sensitivity analyses. RESULTS: Of 563 included patients, 419 (74.4%) underwent IHT from 77 referring facilities, primarily because of absent on-site neurosurgical coverage (74.2%). Compared with direct admission, IHT patients had longer time to aneurysm confirmation (median 3.2 vs 0.8 hours) and fewer ultra-early treatments (<3 hours: 2.4% vs 16.2%). During transfer, neurological deterioration occurred in 10.3% according to the Glasgow Coma Scale, 16.1% according to the World Federation of Neurosurgical Societies scale, and 15.8% according to the Hunt and Hess scale. On paired imaging (n = 307), Fisher grade IV hemorrhage increased from 29.0% to 40.4%, acute hydrocephalus increased from 15.6% to 33.2%, and new-onset hydrocephalus developed in 17.6%. Pretransfer external ventricular drain was uncommon (4.8% overall; 12.5% among patients with hydrocephalus on initial computed tomography in the paired-imaging subset). Favorable discharge outcome was lower in patients with new-onset hydrocephalus and in those with hydrocephalus on both scans than in those without (29.6%/22.9% vs 62.0%; P < .001), and 12-month functional independence was similarly reduced (51.9%/45.7% vs 69.4%; P = .002). CONCLUSION: The transfer interval in aSAH represents a clinically vulnerable phase rather than a passive delay. Paired clinical and imaging data identify in-transit deterioration and hydrocephalus development as associations that warrant prospective investigation and may inform standardized regional transfer pathways; they do not establish intervention targets.