The permeability of the round window membrane during otitis media.

Studies of the permeability of the round window membrane (RWM) during otitis media are important because toxins and cellular components that occur in otitis media as well as pharmacologic agents used in treating the disease have the potential to cross the RWM and pass into the inner ear. Twenty-five cats were evaluated electron microscopically as to the passage of a tracer, horseradish peroxidase, through normal RWMs and RWMs three days, one week, and two weeks following eustachian tube obstruction. Passage at three days following obstruction was similar to passage through the normal RWM. Following one to two weeks of obstruction, the permeability of the membrane was drastically reduced. The reduction in permeability was probably due to the presence of residual effusion overlying the membrane, the presence of granulation tissue within the niche, and a thickening of the RWM.