Associations between early ischemic signs on non-contrast CT and time since acute ischemic stroke onset: A scoping review

Purpose: Onset to imaging (OTI) time is a crucial factor in determining treatment eligibility for acute ischemic stroke patients, since the treatments are time-dependent. Patients with an unknown OTI time are often excluded from treatment, or advanced imaging is needed, which is not widely and readily available. As non-contrast CT (NCCT) is part of the standard stroke protocol, estimating OTI time using only NCCT would be valuable for patients with an unknown OTI time. Early ischemic signs (EISs) visible on NCCT might be fit for this purpose if an association between these signs and OTI time exists. This scoping review aims to provide an overview of the literature that associated OTI time with qualitative or quantitative EISs, including the hyperdense artery sign (HAS), decrease in grey matter-white matter differentiation, hypodensity, and mass effect. Method: The prevalence of the EISs at specific OTI times is assessed, and previously presented associations between the EISs and OTI time are reported. Results: The EIS prevalence varied between the studies. The HAS prevalence decreased after 6 h since onset. The hypodensity prevalence increased with increasing OTI time. Studies quantifying the extent of hypodensity could distinguish patients within and beyond treatment time windows, indicating its potential to estimate OTI time. Finally, mass effect prevalence was seen more often at later OTI times. Conclusions: It is concluded that, despite the high prevalence variability between studies, some associations between EISs and OTI time can be observed. These are potentially valuable in estimating OTI time and supporting treatment decisions.