Spiral ligament and stria vascularis changes in cochlear otosclerosis: effect on hearing level.

OBJECTIVE: To investigate the effect of changes within the spiral ligament and stria vascularis on hearing in cochlear otosclerosis, we examined spiral ligament hyalinization, stria vascularis atrophy, and sensory hearing loss in cochlear otosclerosis and described changes in ion transport molecule expression. STUDY DESIGN: Retrospective. SETTING: Tertiary referral center. PATIENTS: Thirty-two cochleae from 24 temporal bone donors with histologic evidence of cochlear otosclerosis, including spiral ligament hyalinization. INTERVENTION: Audiography. MAIN OUTCOME MEASURES: Measurements of spiral ligament width, stria vascularis, and bone-conduction thresholds were compared by the amount of hyalinization. Expression of the ion transport molecules Na,K-ATPase, connexin 26, and carbonic anhydrase II were assessed by immunohistochemical techniques. RESULTS: Hyalinization most often involved the posterior basal turn (88%) and the posterior middle turn (27%). Spiral ligament hyalinization correlated significantly with stria vascularis atrophy in the posterior middle turn of the cochlea (rho = -0.63, p < 0.01). There was a trend toward a significant association in the posterior basal turn (rho = -0.31, p < 0.08). Bone-conduction thresholds at 2,000 and 4,000 Hz were significantly associated with the amount of stria vascularis atrophy (rho = -0.44, -0.40, p < 0.05). In addition, we observed decreased immunostaining for both carbonic anhydrase II with Type I fibrocytes and Na,K-ATPase with stria vascularis and Type II and Type IV fibrocytes of the spiral ligament in cochlear otosclerosis sections compared with normal cochlea. Na,K-ATPase staining within the stria vascularis was further decreased in the presence of spiral ligament hyalinization. No significant differences were seen with connexin 26 immunostaining. However, immunostaining results were somewhat inconsistent. CONCLUSION: These data suggest that spiral ligament structure and function are essential for stria vascularis survival. In addition, dampened expression of ion transport molecules within the spiral ligament and stria vascularis may disrupt potassium ion recycling, resulting in loss of endocochlear potential and sensory hearing loss.