A study of 1452 human temporal bones revealed a previously unpublished material of 144 bones with otosclerosis. After exclusion of infants and individuals of races other than white, the incidence of otosclerosis was 12.75%. Of the bones with otosclerosis, 56.1% belonged to men and 43.9% to women. The incidence of clinical and histologic otosclerosis was practically the same for men (44.7% to 55.3%) as for women (47% to 53%). However, the incidence of bilateral otosclerosis was higher in women (88.9%) than in men (65.2%). Bilateral otosclerosis was present in 75.6%, whereas it was unilateral in 24.4%. Sixty-six (66) ears (45.8%) had clinical otosclerosis, whereas 78 (54.2%) had histologic otosclerosis--frequently unifocal lesions. The most common site was anterior to the oval window (117 ears, 81.25%), followed by round window niche (52 ears, 36.11%), apical and medial cochlear wall (31 ears, 21.52%), and anterior wall of the internal auditory canal (27 ears, 18.75%). The activity of lesions was directly related to their size. Smaller lesions were predominantly inactive, whereas medium and larger lesions were predominantly active. There was a positive correlation when the size of the lesions, activity, and degree of cochlear endosteal involvement were compared with bone conduction thresholds (37 cases). Correlations between size and activity, and between activity and associated sensorineural hearing loss did not necessarily follow the sequence of an initial active stage (spongiotic) to a final inactive one (sclerotic). Comparison of cases of otosclerosis with equivalent age groups of the normal population yielded worse bone conduction thresholds for the otosclerosis cases only in the age group 60 to 69 years and older. Comparison of average bone conduction thresholds between bones with one site of endosteal involvement (28.26 dB HL) revealed no significant differences. Bones with two or more sites of endosteal involvement had significant differences. Bones with two or more sites of endosteal involvement had significantly worse bone conduction thresholds (62 dB HL). The overall results are not suggestive of an association of sensorineural hearing loss with otosclerosis without stapedial fixation.

An experimental study was conducted in chinchillas regarding the pathogenesis of acquired cholesteatoma (keratoma). The placement of a chemically modified gelatin membrane from the external auditory canal to the promontory through a tympanic membrane perforation stimulated squamous epithelial cell migration. Cholesteatoma formation with the presence of keratin debris and inflammatory reactions was observed in the middle ear and anterior bulla in 53.5% of the experimental animals. These experimental findings show for the first time the presence of epithelial migration and true cholesteatoma formation in the middle ear of chinchillas in an experimental model with deliberate perforation of the tympanic membrane. Erosion of the cochlear walls was observed in areas with granulation tissue and cholesteatoma. The importance and significance of the migration of squamous epithelium and of the middle ear inflammatory reaction in the genesis of acquired cholesteatomas are discussed.

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