In-vitro microCT validation of preoperative cochlear duct length estimation

Variation in human cochlear dimension must be considered when selecting a patient-suitable electrode array for coch-lear implantation. A promising way of cochlear duct length (CDL) prediction utilizes statistical properties of variations in cochlear morphology. In this work, CDL values estimated by statistically derived equations were validated using three-dimensional measurements in micro-CT data sets of seven human temporal bones with implanted electrode arrays. Further, the lateral wall length (LWL) was assessed manually and compared to the prediction of Escudé's equation. Comparison showed good congruency of the measured and predicted CDL and LWL at one turn length (basal turn). Deviations of about 5 % were observed in CDL at 1.5 turn lengths, as well in LWL at 1.5 and 2 turn lengths. Results suggest that CDL prediction based on a single radiographic measurement of the cochlea could support surgeons in electrode array selection, but further investigation with increased sample size is necessary. 1 Problem Knowledge of the patient-specific cochlear duct length (CDL) is particularly important when precise intracochlear electrode array placement is desired. In cases with no residual hearing the surgeon aims to insert the electrode array as deeply as possible in order to achieve a full coverage of the sensory range. In contrast, in cases of patients with residual hearing, electrode arrays are designed to be placed only partially within the cochlea (electric-acoustic stimulation, up to 1.5 turns). Provided that a resistance-free (and atraumatic) insertion can be achieved, the usage of an electrode array with suitable length is crucial for optimal implant placement in both patients with and without residual hearing. Nevertheless , an electrode array inserted the same length in two different cochleae, may result in a completely different insertion depth angle due to variations of the cochlear size. In this context, a preoperative estimation of the CDL could help the surgeon to choose an electrode array suitable for the patient's anatomy and therefore increase the patient's benefit after implantation. The utilization of statistical correlation between the length of the organ of Corti and the size of the cochlea seems to be a possible method for preoperative CDL estimation. The longest diameter of the basal turn (distance 'A') through the round window (RW) and the modiolar axis can be determined by single plane assessments in preoperative radiographs acquired as part of the routine clinical procedure. Based on previous work on cochlear size variation, statistical equations were formulated allowing for an …