Clinical Presentation

Untreated or progressive cerebral herniation can result in increased morbidity and mortality rates. For example, in cases of fulminant hepatocellular failure, cerebral herniation is the leading cause of death and disability. Even in controlled environments such as the operating room, cerebral herniation can be the primary cause of death in approximately 15% of patients.

Patients with elevated intracranial pressure resulting in cerebral herniation require a detailed physical and neurologic examination. Similar to patients presenting with coma, individuals should be evaluated for evidence of head trauma, such as scalp laceration, hemotympanum, otorrhea, and rhinorrhea. The neurologic examination consists of an assessment of the level of consciousness as determined by verbal responses, eye opening, and purposeful movements. Attempts should be made to elicit a behavioral motor response by verbal stimulation alone. If no response follows even shouted commands, noxious stimulation can be applied to the face by digital supraorbital pressure and individually to the arms and legs by compression of distal interphalangeal joints with a nontraumatic object, such as a soft wood tongue blade. Verbal responses are indicative of dominant hemisphere function, and eye opening indicates activity of the reticular activating system.

During the neuroophthalmologic examination, the fundus of each eye should be examined for papillede-ma or hemorrhage. Although episodic anisocoria associated with headaches is usually benign, a unilateral, dilated fixed pupil (sometimes referred to as a "blown pupil'') suggests damage to parasympathetic fibers of the external portion of the third cranial nerve as a result of brain herniation. In contrast, pinpoint pupils suggest compression of pontine structures. Midposition, fixed pupils indicate midbrain failure and loss of both sympathetic and parasympathetic pupillary tone, whether caused by structural or metabolic disease.

As previously described for comatose patients without spontaneous eye movements, doll's eyes responses and the ice water caloric test can be used to determine the integrity of the third, sixth, and eighth cranial nerves and their interconnecting brain stem pathways. If the cortical influences are depressed but brain stem gaze mechanisms are intact, the eyes will deviate conjugately to one side when the head is rotated to the opposite side. When the doll's eyes' responses are absent, it is necessary to perform the ice water caloric test.

The motor examination provides insight into the functional integrity of the neuronal networks linking the cortex, brain stem, and pyramidal tracts. Although diminution of brain stem auditory evoked potentials and somatosensory evoked potentials can be sugges tive of transtentorial brain herniation, the neurologic examination remains the mainstay for assessment of the patient with increased intracranial pressure. The absence of motor response, especially if flaccidity and areflexia are also present, indicates severe brain stem depression. Decerebrate or extensor responses correlate with destructive lesions of the midbrain and upper pons. Decorticate or flexor responses occur after damage to the hemispheres and in metabolic depression of brain function. Withdrawal and localizing responses imply purposeful or voluntary behavior, but the ability to follow commands is considered to be the best response and marks the return of consciousness.

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