==== Front Ann Saudi MedAnn Saudi MedAnnals of Saudi Medicine0256-49470975-4466King Faisal Specialist Hospital and Research Centre 2962054610.5144/0256-4947.2018.125asm-2-125Original ArticleComparison of cochlear duct length between the Saudi and non-Saudi populations Alanazi Alaa aAlzhrani Farid b a College of Medicine, King Saud University, Riyadh, Saudi Arabia b King Abdullah Ear Specialist Center, King Saud University, Riyadh, Saudi ArabiaCorrespondence: Alaa Alanazi, College of Medicne, King Saud University, PO Box 245, Riyadh 11411, KSA, alaa.a.alanazi@gmail.com, ORCID: http://orcid.org/0000-0001-8096-9118Mar-Apr 2018 05 4 2018 38 2 125 129 08 1 2018 06 2 2018 Copyright © 2018, Annals of Saudi Medicine2018This is an open access article under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License (CC BY-NC-ND). The details of which can be accessed at http://creativecommons.org/licenses/by-nc-nd/4.0/BACKGROUND There are no data on cochlear duct lengths (CDL) among Middle East populations. OBJECTIVES The main aims of this study were to estimate the average CDL in the Saudi population and to compare it with the reported CDL in other regions/ethnic groups outside the Middle East. DESIGN Retrospective study. SETTING Tertiary otolaryngology head and neck surgery center. SUBJECTS AND METHODS Temporal bone CT scans were reviewed to determine CDL. We excluded any CT scan of an ear with a congenital inner ear anomaly or acquired pathology. MAIN OUTCOME MEASURES CDL. SAMPLE SIZE 441 temporal bone CT scans. RESULTS The overall CDL mean was 31.9 mm (range 20.3–37.7 mm). The cochleae of males was significantly longer than of females and cochleae from the left side were significantly longer than of the right side. No significant difference was found between children and adults. Inter-study comparison revealed a significant difference in CDL between the Saudi population in our study and European and Australian studies, but not between the present study and North American studies. CONCLUSIONS The CDL differed significantly according to side of the cochlea and sex, but not by age. Geographically and ethnically, the mean CDL for Saudis was significantly different from the CDL of subjects of some ethnic backgrounds, but not others. Due to this diversity, we recommend that the CDL be measured before cochlear implant surgery. LIMITATIONS All the measurements were done by one person, and the subjects’ physical measurements, such as height or head circumference, were not included. ==== Body Cochlear duct length (CDL) is defined as the length of the scala media measured from the middle of the round window to the helicotrema.1 Determining the CDL is important for cochlear implantation. The insertion depth of the cochlear implant (CI) electrode array has been strongly associated with intraoperative trauma.2–4 Shallow insertion is correlated with worse speech performance.5 Due to variations in the size of the human cochlea,6–19 variations in CDL need to be considered before implantation with a fixed length CI electrode. To this end, it would be helpful to know the normal range of CDL in our society. To the best of our knowledge, however, there are no data about the average CDL among the Middle Eastern populations, specifically in the Saudi population. The main aim of this study was, therefore, to estimate the average CDL of the Saudi population, and to compare it with the reported CDL of other nationalities. SUBJECTS AND METHODS In this retrospective study, temporal bone CT scans were reviewed to determine CDL. We excluded any CT scan of an ear with a congenital inner ear anomaly or acquired pathology, e.g. post-meningitis or post trauma cochlear ossification. All study procedures were performed at the King Abdullah Ear Specialist Center (KAESC) at the King Saud University in Saudi Arabia. The study was approved by the institutional review board in King Saud University (project number E-16–1917). The axial views of conventional non-contrast temporal bone CT scans were reviewed using picture archiving and communication system (https://www.wikiwand.com/en/Picture_archiving_and_communication_system). The images were reformatted as 1-mm thick minimum intensity projection. CDL was measured using the equation: CDL=(4.16×A)–3.98,21 where the A value is determined by CT scan as the straight line starting from the midpoint of the round window opening to the opposite side of the cochlea passing through the mid-modiolar axis (Figure 1).15 All measurements were done by the same person. The overall mean and range of CDL were calculated and the mean CDL was compared according to age (children/adolescents ≤18 years or older vs. adults >18 years), sex, and head side (left side cochlea vs. right side cochlea). The data was analyzed using IBM SPSS version 22 (https://www.wikiwand.com/en/SPSS). We tested the normal distribution of the data using the Kolmogorov-Smirnov test. Our data did not follow a normal distribution, so we used a nonparametric test to compare between the groups: the Mann-Whitney Test for independent data (as the sex and age groups) and the Wilcoxon signed ranks test for the dependent data (head side). The overall mean CDL of this study was compared with other published data using independent samples t test, using the published summary statistics—mean, standard deviation and sample sizes since the full data from published studies was not available. RESULTS In 401 temporal bone CT scans (882 cochleae), the sex distribution was 226 females and 215 males. The age distribution was 383 children (≤18 years) and 58 adults. The mean (SD) age of the children was 7.4 (3.6) years and of adults, 37.2 (14.9) years. The overall mean CDL was 31.9 mm (range 20.5–37.7 mm). According to age, no significant difference between children and adults was found in mean CDL (P=.720) or mean CDL in the right (P=.256) and the left side (P=.819) (Table 1). According to the sex, males had a significantly longer mean total CDL (P=.003), mean CDL in the right side (P=.014), and mean CDL in the left side (P=.003) (Table 2). According to head side, the mean CDL in the left side (32.199 mm [2.869]) was significantly longer than in the right side (31.565 mm [2.785]) (P<.0001). DISCUSSION In 1938 Hardy was the first to describe the measurement of CDL 6. Subsequently many articles using different methods to measure the CDL have been published. Debate persists about how to measure CDL. In the present study, we measured the CDL by using the equation at the level of the organ of Corti,21 which is the most applicable and time saving method and it is what we use in the routine practice in our institute. Many studies have found that CDL is not age dependent. 1,7,11,22 Our findings support this as there was no significant difference in CDL between the age groups. We think that these corresponding findings confirm that the age factor has no role in the field of studying the causes of the CDL divergence. We compared the mean CDL in the present study with those reported by other studies (Table 3). No significant difference was found between the present study and North American studies,6,7,20,25 except in one article.11 The mean CDL in European and Australian studies are significantly longer to those obtained in the present study.1,8,9,12,15,17,22 Three studies reported CDL in Asian populations.19,24,26 The first study, presented in poster-format, reported a mean CDL of 29.8 mm (28–34.3 mm),19 the second study reported a significantly smaller CDL than the present study,26 and the third study, published in 2017 measured the CDL in different Asian ethnic populations (Chinese, Malay, and Indian). However, unlike some previous studies,1,22,23 the present study found that CDL differed significantly according to head side, which supports the findings of recent study.24 Furthermore, whereas many studies have found no significant difference in CDL according to sex,7,16,20,25,26 we found that males had a longer CDL than females, which, while potentially controversial, is not a unique finding.1,11,15,24 The ethnic group of the subjects and the geographical area of the studies are factors to consider in studying CDL diversity. While the average CDL of all racial groups has not been reported, extant reports indicate that there is racial variation between Asia populations. This supports our finding of CDL variations between ethnic group and geographic area.24 Why this diversity exists is unclear and is possibly due to a combination of factors. The inter-study variety in modality, sample size, and method of CDL measurements in the studies shown in Table 3 may be partly attributable for the diversity. Furthermore, the physical measurements of the subjects, e.g. height and head circumference, might impact CDL but were not considered in the present study or in the previous studies. We believe that further studies that consider all of these factors are needed to explore this issue. There are several limitations in the present study. Firstly, all measurements were done by the same person, as we tried to mimic the current practice of the surgeons when they estimate the CDL before surgery. Secondly, the subjects’ physical measurements, such as height or head circumference, were not included, although this may provide to be an interesting future study in terms of investigating the relationship between the subjects’ physical measurements and the measured CDL, particularly across different ethnic groups. Finally, future studies will have much to explore variations in cochlear anatomy, specifically CDL, between sex, ethnic groups, and the side of the head. Although conclusions are very much preliminary, that predictable CDL variations do seem to exist underlines the importance of taking a flexible approach to CI insertion depth. Using radiological imaging to predict the CDL before CI surgery to adjust CI insertion depth should help to minimize intraoperative trauma and maximize postoperative speech performance.2–5 In conclusion, in our cohort of 882 cochleae, CDL differed significantly according to side of the cochlea and sex but not age group. Geographically and ethnically, the mean CDL of Saudis was significantly different from the CDL of some subjects of ethnic backgrounds but not others. Due to this diversity, we recommend that CDL be measured before cochlear implant surgery. CONFLICT OF INTEREST: None. Funding: None. Figure 1 Measurement of the A value in the cochlear duct length equation. Table 1 Comparison of child and adult cochlear duct lengths (CDL). Total is the average of left and right side. Mean CDL (± SD) Overall Right side Left side Children (≤18 y) 31.83 (2.73) 31.48 (2.88) 32.17 (2.932) Adults (>18 y) 32.24 (1.95) 32.09 (2.06) 32.38 (2.46) P value .720 .256 .819 Data are mean (standard deviation) in millimeters. Overall is the average of left and right side. Table 2 Comparison between male and female cochlear duct length (CDL). Total is the average of left and right side. Sex Overall Right side Left side Males 32.27 (2.48) 31.95 (2.61) 32.59 (2.75) Females 31.51 (2.75) 31.20 (2.91) 31.82 (2.94) P value .003 .014 .003 Data are mean (standard deviation) in millimeters. Overall is the average of left and right side. Table 3 The different reported means of CDL in the various studies. Authors Modality CDL N Study location P value At the level of Mean in mm (SD) Min/Max Hardy 19386 Histology OC 31.57 (2.3) 25.26/35.46 68 N America .3454 Walby 19857 Histology OC 32.6 (2.1) 30.1/36.4 20 N America .2286 Pollak et al 19878 Histology OC 28.4 (3.4) 24/33.5 9 Europe .0001 Ulehlova et al 19879 Histology OC 34.2 (2.93) 28/40.1 50 Europe .0001 Sato et al 199111 Histology LW 38.64 (3.19) 32.7/43.2 18 N America .0001 Kawano et al 199612 Histology LW 40.81 (1.97) 37.93/43.81 8 Australia .0001 Kawano et al 199612 Histology OC 35.58 (1.41) 34.15/37.9 8 Australia .0001 Ketten et al 199820 CT OC 33.01 (2.31) 29.07/37.45 20 N America .0591 Escudé et al 200615 CT LW 34.4 (2.2) 30.76/37.41 84 Europe .0001 Stakhovskaya et al 200725 Histology OC 33.13 (2.11) 30.5/36.87 9 N America .1588 Erixon et al 200917 Plastic casts LW 42 (1.96) 38.6/45.6 58 Europe .0001 Grover et al 201319 CT LW 29.8 (N/A) 28/34.3 104 Asia No SD Shin et al 201326 Micro CT LW 30 (1.6) N/A 39 Asia .0001 Erixon and Rask-Andersen 201322 Plastic casts LW 42.2 (1.86) 37.6/44.9 51 Europe .0001 Würfel et al 20141 Cone beam CT LW 37.9 (1.98) 30.8/43.2 436 Europe .0001 Thong et al 201724 CT LW Male: 22.32 Female: 21.83 19.71/25.09 314 Asia No Mean, No SD Present study CT OC 31.882 (2.645) 20.45/37.72 882 Saudi Arabia (Asia) N/A OC=organ of Corti, LW=Lateral Wall, CT=computed tomography, SD=standard deviation, N/A=not available, N=number of subjects in the study, N America=North America. ==== Refs REFERENCES 1 Würfel W Lanfermann H Lenarz T Majdani O Cochlear length determination using Cone Beam Computed Tomography in a clinical setting Hear Res 2014 316 10 65 72 10.1016/j.heares.2014.07.013 25124151 2 Welling DB Hinojosa R Gantz BJ Lee J-T Insertional Trauma of Multichannel Cochlear Implants Laryngoscope 1993 103 9 995 1001 10.1288/00005537-199309000-00010 8361322 3 Shepherd RK Pyman BC Clark GM Webb RL Banded Intracochlear Electrode Array: Evaluation of Insertion Trauma in Human Temporal Bones Ann Otol Rhinol Laryngol 1985 94 1 55 59 10.1177/000348948509400112 3838226 4 Kennedy DW Multichannel Intracochlear Electrodes Laryngoscope 1987 97 1 42 49 10.1288/00005537-198701000-00011 3796175 5 Hochmair I Arnold W Nopp P Jolly C Müller J Roland P Deep electrode insertion in cochlear implants: apical morphology, electrodes and speech perception results Acta Otolaryngol 2003 123 5 612 617 10.1080/00016480310001844 12875584 6 Hardy M The length of the organ of Corti in man Am J Anat 1938 62 2 291 311 10.1002/aja.1000620204 7 Walby AP Scala Tympani Measurement Ann Otol Rhinol Laryngol 1985 94 4 1 5 3970499 8 Pollak A Schrott A Methodological Aspects of Quantitative Study of Spiral Ganglion Cells Acta Otolaryngol 1987 104 37 42 10.3109/00016488709124974 9 Úlehlová L Voldřich L Janisch R Correlative study of sensory cell density and cochlear length in humans Hear Res 1987 28 2–3 149 151 10.1016/0378-5955(87)90045-1 3654386 10 Takagi A Sando I Computer-Aided Three-Dimensional Reconstruction: A Method of Measuring Temporal Bone Structures Including the Length of the Cochlea Ann Otol Rhinol Laryngol 1989 98 7 515 522 10.1177/000348948909800705 2751211 11 Sato H Sando I Takahashi H Sexual Dimorphism and Development of the Human Cochlea: Computer 3-D Measurement Acta Otolaryngol 1991 111 6 1037 1040 10.3109/00016489109100753 1763623 12 Kawano A Seldon HL Clark GM Computer-Aided Three-Dimensional Reconstruction in Human Cochlear Maps: Measurement of the Lengths of Organ of Corti, Outer Wall, Inner Wall, and Rosenthal’s Canal Ann Otol Rhinol Laryngol 1996 105 9 701 709 10.1177/000348949610500906 8800056 13 Skinner MW Holden TA Whiting BR In Vivo Estimates of the Position of Advanced Bionics Electrode Arrays in the Human Cochlea Ann Otol Rhinol Laryngol 2007 116 4_suppl 2 24 10.1177/00034894071160S401 14 Adunka O Unkelbach MH Mack MG Radeloff A Gstoettner W Predicting Basal Cochlear Length for Electric-Acoustic Stimulation Arch Otolaryngol Neck Surg 2005 131 6 488 10.1001/archotol.131.6.488 15 Escudé B James C Deguine O Cochard N Eter E Fraysse B The Size of the Cochlea and Predictions of Insertion Depth Angles for Cochlear Audiol Neurootol 2006 11 Suppl 1 27 33 10.1159/000095611 17063008 16 Miller JD Sex differences in the length of the organ of Corti in humans J Acoust Soc Am 2007 121 4 EL151 155 10.1121/1.2710746 17471760 17 Erixon E Högstorp H Wadin K Rask-Andersen H Variational Anatomy of the Human Cochlea Otol Neurotol 2009 30 1 14 22 10.1097/MAO.0b013e31818a08e8 18833017 18 Lee J Nadol JB Eddington K Depth of Electrode Insertion and Postoperative Performance in Humans with Cochlear Implants?: A Histopathologic Study Audiol Neurootol 2010 15 5 323 331 10.1159/000289571 20203481 19 Grover M Mishra P Gupta G Jangid M Cochlear Duct Length: Are We Giving It Adequate Importance? Otolaryngology–Head and Neck Surgery 149 SAGE Publications 2013 219 219 10.1177/0194599813496044a233 23629969 20 Ketten DR Skinner MW Wang G Vannier G Gates G Neely J In vivo measures of cochlear length and insertion depth of nucleus cochlear implant arrays Ann OtolRhinol-LaryngolSuppl 1998 175 11 1 16 21 Alexiades G Dhanasingh A Jolly C Method to Estimate the Complete and Two-Turn Cochlear Duct Length Otol Neurotol 2015 36 5 904 907 10.1097/MAO.0000000000000620 25299827 22 Erixon E Rask-Andersen H How to predict cochlear length before cochlear implantation surgery Acta Otolaryngol 2013 133 12 1258 1265 10.3109/00016489.2013.831475 24053486 23 Pelliccia P Venail F Bonafé A Cochlea size variability and implications in clinical practice 2014 d 42 49 24 Thong J Low D Tham A Liew C Tan T Yuen H Cochlear duct length–one size fits all? Am J Otolaryngol 2017 1 4 10.1016/j.amjoto.2017.01.015 25 Stakhovskaya O Sridhar D Bonham BH Leake PA Frequency map for the human cochlear spiral ganglion: Implications for cochlear implants JARO - J Assoc Res Otolaryngol 2007 8 2 220 233 10.1007/s10162-007-0076-9 17318276 26 Shin K-J Lee J-Y Kim J-N Quantitative Analysis of the Cochlea using Three-Dimensional Reconstruction based on Microcomputed Tomographic Images Anat Rec 2013 296 7 1083 1088 10.1002/ar.22714