[Experimental defects of the round window membrane].

Previous and current studies of experimentally induced fistulas in the round window membrane (RWM) are reviewed. After puncture (or "micro-perforation") of the RWM leaking perilymph was not been observed and auditory evoked potentials have remained unaltered. In contrast, most publications have reported that gross incisions ("macro-perforations") of the RWM have resulted in the deterioration of auditory evoked potentials, with leaking perilymph and/or cerebrospinal fluid and/or with entrance of air bubbles into the scala tympani depending on the site of the perforation. Spontaneous healing was then observed within 4 to 8 days and was associated with normalization of the auditory evoked potentials. In a very few experimental studies pathophysiological mechanisms were simulated that may be involved clinically in patients with RWM fistulas, i.e. implosive rupture of the RWM due to an acute increase in middle ear pressure or explosive rupture of the RWM that may occur in patients trying to use forced Valsalva maneuvers to equalize decreased middle ear pressures due to blocked Eustachian tubes.