Which semicircular canal is the LEAST commonly involved in benign paroxysmal positional vertigo, and what is the typical direction of the positional nystagmus when it is affected?

• A Posterior canal, with upbeating torsional nystagmus
• B Anterior (superior) canal, with predominantly downbeating nystagmus ✓
• C Lateral canal, with horizontal geotropic nystagmus
• D Posterior canal, with purely horizontal nystagmus

Explanation

The anterior or superior canal accounts for roughly 1 to 2 percent of BPPV cases because it is anatomically uppermost when upright, so debris rarely enters or settles in it. Its positional nystagmus is characteristically downbeating, usually with a small torsional component, since ampullofugal flow in the anterior canal inhibits it. Posterior canal BPPV gives upbeating torsional nystagmus, and lateral canal involvement gives horizontal nystagmus, making those options internally inconsistent here.

Reference: Dhingra's Diseases of Ear, Nose and Throat, 8th ed.

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Written and medically reviewed by the StethoPrep medical team.