In vestibular testing, a positive head thrust test indicates what?

• A. A deficit in the vestibulo-ocular reflex on the tested side
• B. A deficit in the semicircular canal–oculomotor pathway on the tested side
• C. Central cerebellar lesion
• D. Normal vestibular function

Answer: (B)

The head thrust test looks at the high-frequency vestibulo-ocular reflex that connects each semicircular canal to the eye muscles. When you rapidly turn the head to one side, a normal VOR should keep the eyes on target. If there’s a unilateral dysfunction affecting the input from the semicircular canals or the canal–oculomotor pathway on the tested side, the VOR can’t generate the needed eye movement, so the eyes drift off target and a corrective saccade is needed to refixate. That pattern—an eye slip followed by a corrective catch-up saccade—signals a deficit in the semicircular canal–oculomotor pathway on the tested side. Central cerebellar lesions and normal vestibular function don’t produce this characteristic corrective response.