A 52-year-old woman presents with a 6-month history of episodic vertigo lasting 30–45 minutes, accompanied by a low-pitched roaring tinnitus and sensation of ear fullness. Between episodes, she reports complete resolution of symptoms. Audiometry reveals the pattern marked **A** in the diagram—unilateral low-frequency sensorineural hearing loss with a rising curve (better hearing at high frequencies). Repeat audiometry 3 weeks later shows different thresholds at low frequencies. Which of the following best explains the pathophysiology underlying this audiometric pattern?