Following head trauma, which exam finding most likely indicates early uncal herniation?

• A. Absent oculovestibular reflex
• B. Bilateral pinpoint pupils
• C. Gaze preference away from the lesion
• D. Unilateral dilated and fixed pupil

Answer: (D)

The earliest sign of uncal herniation is compression of the oculomotor nerve on the same side as the herniation. The parasympathetic fibers that constrict the pupil run on this nerve and are especially vulnerable to squeezing. When these fibers are affected, the pupil on that side becomes dilated and nonreactive to light, even before other brainstem signs appear. This is why a unilateral dilated and fixed pupil after head trauma is the most concerning early exam finding and points to impending herniation.

Other findings reflect different problems or later stages. Absent oculovestibular reflex points to brainstem dysfunction but isn’t the earliest sign of uncal herniation. Bilateral pinpoint pupils suggest pontine injury or drug effect, not unilateral third-nerve compression. Gaze preference away from the lesion is more typical of a cortical or hemispheric process rather than early uncal herniation.