Unilateral absence of the acoustic reflex due to left-sided VIIth nerve pathology would be best described as which of the following?

• A. Conduction loss in the left ear
• B. VIIIth nerve pathology left
• C. VIIth nerve pathology left
• D. Sensorineural loss in the right ear

Answer: (C)

The key idea is how the acoustic reflex arc works and how to localize a problem within it. The reflex is triggered when a sound enters the ear, sending an afferent signal through the cochlea and VIIIth nerve to the brainstem, and then an efferent signal travels back through the VIIth (facial) nerve to the stapedius muscle to cause contraction. If the left facial nerve is damaged, the left stapedius cannot contract, so the acoustic reflex is absent on the left side.

That’s why describing the issue as left-sided VIIth nerve pathology best fits the finding. It points to a problem in the efferent limb on the left, which directly explains the unilateral reflex absence. The other statements don’t align with this pattern: a conductive hearing loss would mainly alter hearing thresholds and middle-ear conduction, not selectively abolish the reflex due to a facial nerve lesion; VIIIth nerve pathology would affect the afferent limb and produce a different reflex pattern depending on the testing setup; a right-ear sensorineural loss describes a lesion on the right side, not the left.