Emergency Medical Technician (EMT) Intermediate Practice Exam

A 20-year-old male with a traumatic brain injury has one fully dilated, non-reactive pupil. This suggests damage to which part of the brain?

1. Right cerebral hemisphere

2. Left cerebral hemisphere

3. Cerebellum

4. Brainstem

The correct answer is: Left cerebral hemisphere

In the case of a traumatic brain injury where one pupil is fully dilated and non-reactive, this often suggests damage to a specific area of the brain known for its role in pupil response. When examining pupil reaction, particularly in cases of brain injury, the autonomic pathways that control the pupils can be affected by injury or swelling in particular regions. The dilation and lack of reactivity of one pupil can indicate damage to the oculomotor nerve, which is primarily responsible for constricting the pupil and controlling eye movements. The oculomotor nerve originates in the midbrain, which is part of the brainstem. If one side is affected, it often correlates with damage in the opposite hemisphere of the brain, particularly in the area where the nerve fibers traverse. In this scenario, the response strongly points to potential damage on the left side of the brain, which would lead to optical alterations on the right side (as the pathways cross). This can occur in scenarios involving diffuse axonal injury or increased intracranial pressure affecting the brainstem and the midbrain area where the oculomotor nerve resides. Therefore, the interpretation of a fully dilated and non-reactive pupil suggests significant potential injury localized to the brainstem or compression