Brain death: Radiologic signs of a non-radiologic diagnosis

Brain death is a clinical diagnosis characterized by the irreversible loss of neurologic function caused by global injury to the brain, including the brain stem. This is often caused by trauma and subarachnoid hemorrhage amongst other etiologies. This injury results in extensive cerebral edema, a rise in intracranial pressure, and eventual cessation of cerebral blood flow. Although brain death is a clinical diagnosis, ancillary and confirmatory tests are widely used. These are categorized into imaging that demonstrates absence of cerebral blood flow and electroencephalography that demonstrates absence of cortical electrical activity. Cerebral angiography, transcranial Doppler, and cerebral scintigraphy are the only imaging studies to have been validated by the American Academy of Neurology for diagnosis of brain death. However, characteristic findings on computed tomography, computed tomography perfusion, computed tomography angiography, magnetic resonance imaging, and magnetic resonance angiography may suggest the diagnosis. In this article, the clinical criteria, pathophysiology, pathology, and variations in current practice of brain death diagnosis are discussed, and the imaging findings of brain death are reviewed.