High-resolution computed tomographic evaluation of the cochlear capsule in otosclerosis: relationship between densitometry and sensorineural hearing loss.

Otosclerotic cochlear involvement is a rather frequent disease that has not been clearly understood in terms of diagnosis and management. Objective evaluation methods are needed to confirm the clinical diagnosis, investigate the relationship with hearing impairment, and validate the results of treatment. In this study two ear groups with bone conduction hearing loss (BCHL) were investigated with audiometry and high-resolution computed tomography (HRCT). In the first group (n = 22) the diagnosis of fenestral otosclerosis was confirmed at operation; the second group (n = 9) was composed of ears clinically suspicious for purely cochlear involvement. Additionally, a control group (n = 14) of otologically normal ears was also studied. Foci of demineralization were demonstrated in 58% of the ears in the two groups; the sensorineural hearing loss (SNHL) in those ears was significantly worse than in those with normal radiologic findings. Three methods of HRCT densitometry were used to determine the abnormal regions in the cochlear capsule; the results suggested that hypodense regions were consistent with a greater degree of SNHL, in contrast to the hyperdense ones in ears with better cochlear reserves. Agreement was found between the location of the density change and the frequency topography of the SNHL; densitometric values were correlated with the bone conduction thresholds for certain frequencies. It is concluded that the spongiotic foci are responsible for the SNHL, since there was a correlation between their location and the SNHL frequency. The determination of better hearing in those ears with sclerotic foci supports the hypothesis that the sclerotic phase may not be a healing process following the spongiotic phase, and that it can be the first stage of the disease.