In this issue of JAMA Neurology, Boulouis et al1 report on the crucial influence of pretreatment collateral blood vessel status in determining the benefit of transfer for endovascular thrombectomy for large vessel acute ischemic stroke. All patients had relatively little evidence of irreversible injury on noncontrast computed tomography (CT) at their referring hospitals. However, when imaging was repeated at the comprehensive stroke center, a substantial proportion of patients had evolved large infarcts that caused them not to proceed to endovascular therapy or foreshadowed a poor outcome. These data contribute to the weight of evidence that, at a minimum, aortic arch to cerebral vertex CT angiography (CTA) should be performed immediately after the noncontrast CT of the brain at the first hospital that assesses the patient.