The delayed spectral sign in Post-transfer CT imaging: an imaging marker of stroke severity and hemorrhagic risk.

Purpose: Acute stroke transfer patients often undergo repeat computed tomography (CT) imaging upon arrival at a thrombectomy-capable center. Often, there is residual intravenous (IV) "contrast staining" of acute infarcts on the initial post-transfer CT head exam, which we have detected utilizing dual-layer CT spectral virtual non-contrast images. We term this the delayed spectral sign (DSS). We sought to measure the incidence of the DSS on initial post-transfer CT head exams and evaluate for any associated clinical outcomes.

Methods: We performed a retrospective study of acute stroke transfer patients with residual IV contrast on initial post-transfer CT spectral scanner head exams. Two neuroradiologists independently reviewed CT head exams and virtual non-contrast images to measure the incidence of the DSS. Data was analyzed to evaluate significant differences between DSS and non-DSS groups.

Results: 67 acute stroke transfer patients met inclusion criteria, of whom 8 (11.9%) demonstrated the DSS. Patients with the DSS were more likely to have a large vessel occlusion (100% vs. 64.4%, P = 0.049) and an M1 middle cerebral artery (MCA) occlusion (OR 4.9, P = 0.046). DSS patients had a greater prevalence of intracranial hemorrhage on follow-up CT or magnetic resonance imaging (MRI) exams (OR 9.259, P = 0.008). DSS patients had a higher average National Institute of Health Stroke Scale (NIHSS) upon discharge (22.25 ± 18.3), although this was not statistically significant (P = 0.079). In multivariate regression analyses, DSS was positively associated with intracranial hemorrhage on inpatient follow-up CT or MRI (OR 9.683, P = 0.012).

Conclusion: The delayed spectral sign is associated with greater incidences of large vessel occlusions and intracranial hemorrhage on follow-up head imaging.