Variations in microanatomy of the human modiolus require individualized cochlear implantation

Abstract

Cochlear variability is of key importance for the clinical use of cochlear implants, the most successful neuroprosthetic device that is surgically placed into the cochlear scala tympani. Despite extensive literature on human cochlear variability, few information is available on the variability of the modiolar wall. In the present study, we analyzed 108 corrosion casts, 95 clinical cone beam computer tomographies (CTs) and 15 µCTs of human cochleae and observed modiolar variability of similar and larger extent than the lateral wall variability. Lateral wall measures correlated with modiolar wall measures significantly. ~ 49% of the variability had a common cause. Based on these data we developed a model of the modiolar wall variations and related the model to the design of cochlear implants aimed for perimodiolar locations. The data demonstrate that both the insertion limits relevant for lateral wall damage (approximate range of 4–9 mm) as well as the dimensions required for optimal perimodiolar placement of the electrode (the point of release from the straightener; approximate range of 2–5mm) are highly interindividually variable. The data demonstrate that tip fold-overs of preformed implants likely result from the morphology of the modiolus (with radius changing from base to apex), and that optimal cochlear implantation of perimodiolar arrays cannot be guaranteed without an individualized surgical technique.

Insertion trauma of a novel inner ear catheter for intracochlear drug delivery

“…Angular insertion depths of electrode carriers, expressed in degrees around the modiolus, vary due to interindividual anatomical differences, even if arrays of the same lengths are used ( 26 , 27 ). In humans, the height of the scala tympani starts to decrease at around 19 mm, reaching a critical point at approximately 23 mm, at an insertion angle of approximately 450 degrees measured from the round window ( 28 ).…”

On the interdependence of insertion forces, insertion speed, and lubrication: Aspects to consider when testing cochlear implant electrodes

“…Furthermore, there are characteristic ST properties (i.e. shape, length, cross sectional area) that can vary substantially between individuals [ 34 , 36 – 38 ]. This is highly relevant, as was shown by Dhanasingh et al [ 39 ], who showed that smaller sized ST phantoms yield higher insertion forces across different electrode array lengths.…”

Anatomical Variations of Modiolus in Relation with Vestibular and Cranial Morphology on CT Scans

“…An improved understanding of the position of the SCCs in space, based on a scannographic study, could make it possible to adapt vestibular functional explorations, in particular, head movements during VOR studies using the video head impulse test (VHIT). Numerous studies have focused on the anatomy of the cochlea [4,[7][8][9][10]. These studies have shown a great variability of the anatomy but with concordant results.…”

“…These studies have shown a great variability of the anatomy but with concordant results. The methods of study were varied: either by indirect methods by multiple sections of the cochlea or by scannographic or µCT studies [4,[7][8][9][10]. The cochlear duct has a length of between 3.2-4.2 cm with high interindividual variability (relative standard deviation (RSD) > 1000% for the length of the basal turn and RSD > 800% for the total visible length of the cochlear duct) [4,7,8].…”