UCLA

Objective

To evaluate for potential causes of delayed loss of residual hearing that variably occurs with hybrid cochlear implants.

Study design

Histopathological evaluation of 29 human temporal bone (HTB) with cochlear implant (CI).

Setting

The Neurotology and House HTB Laboratory of UCLA (House-UCLA).

Subjects and methods

HTB from CI patients from the House-UCLA HTB Laboratory (n = 28) and one courtesy of Massachusetts Eye and Ear Infirmary (MEEI). Histopathological analysis to identify the location of cochleostomy, fibrosis, and bone formation in the scala vestibuli and tympani, and endolymphatic hydrops. Spiral ganglion neuron counts were obtained. Statistical analysis compared presence of cochleostomy and location with the histopathological findings.

Results

Seventeen of 29 bones with fibrosis in the scala vestibule (SV) and tympani had evidence of a cochleostomy involving the SV containing the ductus reunions, all of which had hydrops. Ten of 11 bones had no SV fibrosis, and a cochleostomy limited to the scala tympani, of which all had no hydrops. One HTB had moderate SV fibrosis not involving the ductus reuniens, and was without hydrops. One HTB had a SV cochleostomy but the electrode ruptured Reissner's membrane, and was without hydrops. Cochleostomy was significantly associated with SV fibrosis and hydrops (p < 0.01), those without hydrops had no SV atrophy (p < 0.01). Round window insertion was associated with no fibrosis and no hydrops.

Conclusion

We hypothesize that cochleostomies involving scala vestibuli incite fibrosis, compromising the ductus reuniens, causing hydrops which may cause the delayed loss of residual low frequency hearing in CI.