What assessment finding is indicative of impending herniation syndrome?

Impending herniation syndrome is a critical condition that occurs when there is an increased intracranial pressure leading to brain tissue displacement. A key assessment finding indicative of this condition is a unilaterally fixed and dilated pupil. This finding suggests that there is likely compression of the oculomotor nerve (cranial nerve III) due to increased pressure within the skull. The affected pupil cannot respond to light or accommodation, indicating significant neurological compromise.

In contrast, fixed and dilated pupils bilaterally can also indicate severe brain injury or increased intracranial pressure; however, it does not specify lateralization, which may be important for determining the pattern of herniation. Constricted pupils are generally not associated with herniation syndrome; instead, they may be indicative of other conditions, such as narcotic use or pontine lesions. Reactive pupils suggest that the brain is responding appropriately to light, indicating that significant pressure-related compromise is not present. Hence, the presence of a unilaterally fixed and dilated pupil is the most specific indicator of impending herniation syndrome due to its direct association with the pathophysiology of increased intracranial pressure.