English: FIGURE 1. “Third window” mechanism due to SCD and enlarged vestibular aqueduct. Schematic representations illustrate inner ear volume velocity with arrows. (A) Normal anatomy allows volume velocity across the cochlear partition from the oval to the round window (two windows). (B) Air conducted sound stimulation results in volume velocity from the stapes to be shunted toward the SCD (third window) and away from the cochlea, resulting in increased air-conduction thresholds at low frequencies and/or sound-induced vertigo (Tullio's phenomenon). Positive static pressure in the middle-ear cavity may result in ampullofugal fluid motion exciting the ampulla, resulting in nystagmus (Hennebert sign) and oscillopsia/vertigo (1, 2, 8–12). (C) Elevated intracranial pressure from Valsalva against closed glottis (e.g., straining, heaving lifting) may result in ampullopetal endolymphatic fluid motion, inhibition of the ampulla, also leading to nystagmus (Hennebert sign) and oscillopsia/vertigo (1, 8, 11). (D) Enlarged vestibular aqueduct (EVA) can also act as a third window, shunting volume velocity away from the cochlear partition and toward the widened vestibular aqueduct (2, 13–15). *Modified from Cheng et al. (16) and Rosowski et al. (8).