Neuroimaging in Coma, Brain Death, and Related Conditions

Coma is a state of unresponsiveness to external stimuli, which can be secondary to a va-riety of CNS alterations affecting essential neuronal pathways, particularly the ascending reticular activating system. A comprehensive clinical evaluation is necessary for assessment of motor function and brainstem reflexes but is often insufficient for determination of the underlying etiology and extent of injury. Diagnostic brain imaging is typically needed for management and decision-making, particularly in acute settings where prompt diagnosis of reversible/treatable conditions is essential, as well as for prognostication. Understanding the pathophysiologic mechanisms leading to coma and comalike states and their imaging manifestations will enable selection of appropriate modalities and facilitate a clinically relevant interpretation. For evaluation of brain death, diagnostic imaging has a supportive role, and when indicated, selection of an ancillary diagnostic test is based on multiple factors, including susceptibility to confounding factors and specificity, in addition to safety, convenience, and availability. Learning objective: To describe the pathophysiology of alterations of consciousness and discuss the role of neuroimaging modalities in the evaluation of coma, brain death, and associated conditions.