Advanced neuroimaging in stroke patients: prediction of tissue fate and hemorrhagic transformation.

Stroke is the second greatest cause of mortality worldwide after ischemic heart disease. It is also the leading cause of disability in industrialized countries. According to the WHO, 15 million people worldwide suffer a stroke annually. It is very difficult to distinguish between an ischemic and a hemorrhagic stroke on a clinical basis, therefore imaging (computed tomography or MRI) plays a central role in the evaluation of patients with acute stroke symptoms. Because of significant advances over the last decade, imaging now provides information beyond the mere presence or absence of intracerebral hemorrhage. Comprehensive neurovascular imaging protocols using computed tomography or MRI can be acquired within minutes, helping to distinguish stroke etiology and guiding treatment decisions for acute reperfusion therapies. The purpose of this article is to give an overview of diagnostic information provided by neuroimaging in the setting of acute stroke, especially ischemic stroke, including information about brain tissue viability status and blood-brain barrier permeability. We will discuss the indications of the current treatment options for stroke, and how imaging influences treatment decision. We will organize our discussion around the concept of the 'four Ps' (parenchyma, pipes, penumbra and permeability) proposed by Howard Rowley, which is an excellent guide for understanding the underlying causes and pathophysiology of ischemic stroke.