During bithermal caloric testing on videonystagmography, warm water (44 degrees Celsius) is irrigated into the left external auditory canal of an alert, fixationsuppressed patient. The expected nystagmus is:
- A Horizontal, fast phase directed toward the right
- B Horizontal, fast phase directed toward the left ✓
- C Purely vertical, fast phase upward
- D Torsional only, with no horizontal component
Correct answer: B. Horizontal, fast phase directed toward the left
Explanation
Warm irrigation creates ampullopetal endolymph flow in the horizontal canal, exciting the ipsilateral vestibular system, so the fast phase beats toward the irrigated ear. The mnemonic COWS states Cold water produces nystagmus with fast phase Opposite, Warm water Same side as the irrigated ear. Cold water on the left would therefore produce a right-beating response, which is the trap behind option A.
Reference: Cummings Otolaryngology: Head and Neck Surgery, 7th ed.
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Written and medically reviewed by the StethoPrep medical team.