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A 49-year-old man presents to you with concerns about a sudden hearing loss in his left ear. He was watching TV with his wife the previous night when he went to the bathroom. Upon returning, he noticed that he could no longer hear speech or music from his left ear and instead, he could only hear a loud hissing sound.

Upon examination, both ears, ear canals, and tympanic membranes appear normal. Combined Weber’s and Rinne’s tests reveal that he has a sensorineural hearing loss on the left side.

What is the most probable cause of this man’s symptoms?