Extraneous round window membranes and plugs: possible effect on intratympanic therapy.

Recently there has been increasing interest in the possibility of treating inner ear disorders by application of medication into the middle ear on the premise that it will diffuse through the round window membrane into the inner ear. We examined 202 temporal bones from 117 patients to determine the frequency of round window niche obstruction. Patients ranged in age at the time of death from 31 to 97 years. Eleven percent of the ears were found to have fibrous tissue or a fat plug, and 21% had an extraneous (false) round window membrane. Of the 85 patients from whom both temporal bones were examined, 56% had no obstruction in either ear, while 22% had obstruction in both ears. We conclude that anatomic variations of the round window niche may explain the wide variations found in dosage of medication required to produce a clinical result.