Histopathology of Inner Ear Malformations: Important Considerations for Cochlear Implant Surgery.

OBJECTIVE

To examine the histopathologic features of inner ear malformations (IEMs) and their implications for cochlear implant (CI) surgery, focusing on neural tissue preservation and electrode selection.

STUDY

DESIGN

Retrospective histopathologic case series analysis.

SETTING

Tertiary academic center.

PATIENTS: Twenty-three temporal bones (ears) with IEMs were identified, from which 7 representative cases (some bilateral, some unilateral), including 2 incomplete partition type I (IP-I), 1 IP-II, 1 IP-III, and 3 cochlear hypoplasia cases are described in detail.

INTERVENTION: None.

MAIN OUTCOME MEASURES: Microscopic assessment of cochlear structures relevant to CI surgery, including modiolar development, neural tissue presence and location, spiral ganglion cell distribution, and interscalar septum integrity.

RESULTS

Neural tissue was present in malformed cochleae despite the absence of bony structures in several cases. IP-I specimens demonstrated spiral ganglion cells predominantly in the internal auditory canal fundus. IP-II and IP-III cases showed unprotected neural tissue in the cochlear center. Cochlear hypoplasia cases exhibited variable neural development, ranging from well-developed to hypoplastic cochlear nerves and reduced spiral ganglion cells.

CONCLUSIONS

Histopathologic findings suggest that lateral wall electrodes may be preferable for many IEM cases to avoid damage to unprotected neural tissue. Electrode selection should be individualized based on the type of malformation, particularly considering compressed or shortened arrays in cases of cochlear hypoplasia. Neural tissue preservation despite bony malformation supports the potential for successful CI outcomes in IEM cases when appropriate surgical techniques and electrode choices are employed.