Trans-impedance matrix heatmap patterns in cochlear implant patients with different cochlear pathologies: meningitis, otosclerosis, and temporal bone fractures.

PURPOSE: Transimpedance matrix (TIM) imaging is an electrical field-based modality that visualizes intracochlear current spread and may detect electrode malposition and subtle cochlear pathology beyond radiological resolution. This study aimed to evaluate etiology-specific TIM heatmap patterns in adult cochlear implant recipients and to assess the utility of TIM as an adjunct to conventional imaging.

METHODS

This observational retrospective case series included 11 adult cochlear implant recipients (15 implanted ears) with defined etiologies: head trauma/temporal bone fracture (5 ears), post-meningitis deafness (5 ears), and cochlear ossification or otosclerosis (5 ears). Preoperative CT and/or MRI confirmed pathology, and postoperative X-ray verified electrode position. TIM measurements were obtained using Cochlear® CustomSound EP software. A normal TIM pattern was defined as a continuous diagonal gradient from bottom-left to top-right. Deviations from this pattern were analyzed and correlated with etiology and radiological findings.

RESULTS

Distinct etiology-related TIM deviations were identified. Trauma cases showed off-diagonal irregularities and signal dissociation suggestive of fractures or over-insertion, including one abnormal TIM with normal imaging. Post-meningitis ears commonly demonstrated off-diagonal signal loss or apical attenuation without radiological correlations. Severe ossification with under-insertion produced an Ocean Pattern of low potentials, whereas one otosclerosis case preserved a normal diagonal pattern configuration.

CONCLUSION

TIM imaging is highly sensitive to changes in tissue conductivity and electrode-tissue interface integrity, enabling detection of early fibrosis or ossification not visible on standard imaging. TIM may serve as a useful adjunct in postoperative cochlear implant evaluation. Further prospective validation is required.