Brain death and the brainstem.

Brain death/death by neurologic criteria (BD/DNC) represents a distinct state after a catastrophic brain injury. In the 19th century, anatomists and physiologists progressively began to sustain the conception of the brainstem as a mediator of vital physiologic functions. A primary supratentorial brain lesion usually provokes a rostrocaudal transtentorial brain herniation syndrome, resulting in brain function impairment in both cerebral hemispheres and the brainstem. When a secondary brain lesion (i.e., cerebral hypoxia) is present, the brainstem, like the forebrain, is also affected. Nevertheless, some patients with a primary infratentorial brain lesion may retain cerebral blood flow and electroencephalographic (EEG) activity without a significant increment of intracranial pressure. Jahi McMath was declared brain-dead, leading to a legal controversy about keeping life-support despite the BD/DNC diagnosis. She presented a huge lesion in the brainstem, but ancillary tests, performed nine months after the initial brain insult, showed conservation of intracranial structures, EEG activity, and autonomic reactivity to the "Mother Talks" stimulus, rejecting the BD/DNC diagnosis. Jahi represented a new state of disorder of consciousness, nonpreviously described, termed "responsive unawakefulness syndrome."