The development of delayed cerebral ischemia after subarachnoid hemorrhage is one of the most important determinants of poor neurologic outcome. The pathophysiology of delayed cerebral ischemia relies on a complex interplay between a significant reduction of the diameter of large intracranial arteries (vasospasm), microvascular disturbances, and spreading cortical depolarization that lead to an inadequate oxygen supply to the brain parenchyma. The early diagnosis of cerebral vasospasm is a real challenge for clinicians and requires a multimodal approach to evaluate the consequences of vascular narrowing on cerebral function. Considering the costs and limited availability of invasive techniques, noninvasive tools may provide continuous and reliable information to detect vasospasm in patients with subarachnoid hemorrhage. In this article, we review in particular the role of transcranial Doppler ultrasonography, cerebral near-infrared spectroscopy, and brain imaging to detect cerebral vasospasm and delayed cerebral ischemia in this patients' population.
