Predicting Basal Cochlear Length for Electric-Acoustic Stimulation

Abstract

To assess the feasibility and accuracy of predicting electrode insertion depth necessary in cochlear implantations for electric-acoustic stimulation by means of preoperative high-resolution computed tomography (HRCT). Design: Human temporal bone study with evaluation of cochlear dimensions. Setting: Tertiary care medical center. Methods: Eight fresh human temporal bones were scanned, and basal cochlear structures were reconstructed and measured. Standard cochlear implantations with a free-fitting array were performed, and the bones then underwent histologic analysis using a technique that allows sectioning of undecalcified bones. After embedding, all bones underwent conventional radiologic analysis with further insertion measurements. Preimplantation HRCT data were compared with radiologic and histologic data. Results: Preimplantation HRCT-based measurements correlated very well with postimplantation radiologic data. A mean failure of 0.3 mm was found. Mean values for the first 360°ranged from 18.8 to 22.0 mm. Conclusions: Preimplantation HRCT-based prediction of cochlear implant insertion depths is both feasible and accurate. It is especially useful when aiming for hearing preservation, where insertion depths of 360°are necessary.

Ganglion Cell and ‘Dendrite’ Populations in Electric Acoustic Stimulation Ears

“…This represents the length of an electrode reaching one turn to approximately 1 kHz. These results are in accordance with those by Adunka et al (2005) and Gstoettner et al (2006) who found that a 360-degree insertion of the array entering this region, which defines the end of electric stimulation and beginning of acoustic stimulation, corresponds to 18–24 mm. This depth was found to provide good cochlear implant performance for both combined EAS and electrical stimulation alone in case of loss of residual hearing without the need for re-implantation.…”

Comment on “The Effect of Cochlear Size on Cochlear Implantation Outcomes”

“…Also, unlike the literature, the authors found a relationship between cochlear length and implant success in the group in which they applied short electrodes [5]. It is unlikely that this result can be explained with electrode selection because there are results in the literature that suggest that smaller cochleae may contain fewer spiral ganglion cells [6,7]. If the short electrode was selected for the long cochlea, the implant success would be expected to be unsatisfactory due to the patient's incompatibility with specific tonotopy [5].…”

Method to estimate the basal turn length in inner ear malformation types

“…The LW can be manually tracked/measured for an angular depth of 360° from clinical CT images in the oblique coronal view, and this has been reported in NA cochleae by Adunka et al 12 . This motivated us to manually measure the BTL (360°) following the LW from 95 datasets, including IEM types of EVAS; IP types I, II, III; and CH, and compare it with the NA cochleae.…”