Unilateral non-reactive pupils in traumatic brain injury most likely indicate what prognosis?

• A. Mild concussion with good recovery
• B. Severe brain injury with poor prognosis; possible brain herniation
• C. Normal variation
• D. Indication of recovery

Answer: (B)

Unilateral non-reactive pupils after traumatic brain injury point to mass effect with brainstem compression, a dangerous situation known as herniation. When pressure rises on one side, the oculomotor nerve (cranial nerve III) can be compressed. Its parasympathetic fibers control the pupil’s constriction, so crushing them causes a dilated, unreactive pupil on that side. This is a sign that intracranial pressure is severely elevated and the brain is at risk of herniation, which correlates with a poor outcome and often requires urgent neurosurgical intervention.

In contrast, a mild concussion typically wouldn’t produce a fixed, dilated pupil, a normal variation would not present with such a focal deficit, and a sign indicating recovery would be the opposite of a fixed, non-reactive pupil.