Research Article Tomography-aided Anthropometric Measurements of External Auditory Canal from Birth to Adulthood

Research Article Tomography-aided Anthropometric Measurements of External Auditory Canal from Birth to Adulthood | Authorea try { document.documentElement.classList.add('js'); } catch (e) { } var _gaq = _gaq || []; _gaq.push(['_setAccount', 'G-8VDV14Y67G']); _gaq.push(['_trackPageview']); (function() { var ga = document.createElement('script'); ga.type = 'text/javascript'; ga.async = true; ga.src = ('https:' == document.location.protocol ? 'https://ssl' : 'http://www') + '.google-analytics.com/ga.js'; var s = document.getElementsByTagName('script')[0]; s.parentNode.insertBefore(ga, s); })(); Skip to main content Preprints Collections Wiley Open Research IET Open Research Ecological Society of Japan All Collections About About Authorea FAQs Contact Us Quick Search anywhere Search for preprint articles, keywords, etc. Search Search ADVANCED SEARCH SCROLL This is a preprint and has not been peer reviewed. Data may be preliminary. 15 July 2025 V1 Latest version Share on Research Article Tomography-aided Anthropometric Measurements of External Auditory Canal from Birth to Adulthood Authors : Ofir Zavdy 0000-0002-4381-216X [email protected] , Lirit Levi , meirav sokolov , Hanna Kabatiansky , Daniella Fadida , Eyal Yosefof 0000-0001-8211-9774 , Leah Fostick , and Ohad Hilly Authors Info & Affiliations https://doi.org/10.22541/au.175255758.80046546/v1 358 views 175 downloads Contents Abstract Supplementary Material Information & Authors Metrics & Citations View Options References Figures Tables Media Share Abstract Introduction The accurate dimensions of the external auditory canal (EAC) have clinical significance in the planning of trans-meatal and endoscopic-assisted otoneurologic surgeries, as well as during the design of hearing aids, otologic tools etc. We sought to assess the anatomical changes in the EAC that occur in the process of maturity from birth to old age. Methods Measurements of 163 thin-sliced CT scans were taken using three planes: axial, parallel and perpendicular to the EAC. Results Seventy-four percent of the cohort consisted of children under 18 years old. Some of the changes from birth to adulthood (18 years) that occurred in the EAC included an increase in overall length from 12.1±1.5 mm to 19.3 ± 3.8 mm. At 10 years, the EAC reached 90% of the adult length. The osseous canal length significantly increased laterally to the isthmus, while the distance between the isthmus and the annulus remains relatively constant. EAC ossification did not occur in most infants (97%) during the first year of life. The curvature of the EAC increased (canal angle changed from 182.5° to 151.3°). A strong correlation was seen between the isthmus and meatal areas. At age 9, the width of the isthmus reaches 90% of the adult size. Conclusion We introduce a standardized system to measure and report on different parameters in the EAC. In-office approximated assessments of the isthmus and overall length, using the meatal area, may be invaluable for pre-surgical planning. The near-adult size (90%) of the EAC is reached at 10 years. Research Article Tomography-aided Anthropometric Measurements of External Auditory Canal from Birth to Adulthood Introduction The accurate dimensions of the external auditory canal (EAC) have clinical significance in the planning of trans-meatal and endoscopic-assisted otoneurologic surgeries, as well as during the design of hearing aids, otologic tools etc. We sought to assess the anatomical changes in the EAC that occur in the process of maturity from birth to old age. Methods Measurements of 163 thin-sliced CT scans were taken using three planes: axial, parallel and perpendicular to the EAC. Results Seventy-four percent of the cohort consisted of children under 18 years old. Some of the changes from birth to adulthood (18 years) that occurred in the EAC included an increase in overall length from 12.1±1.5 mm to 19.3 ± 3.8 mm. At 10 years, the EAC reached 90% of the adult length. The osseous canal length significantly increased laterally to the isthmus, while the distance between the isthmus and the annulus remains relatively constant. EAC ossification did not occur in most infants (97%) during the first year of life. The curvature of the EAC increased (canal angle changed from 182.5° to 151.3°). A strong correlation was seen between the isthmus and meatal areas. At age 9, the width of the isthmus reaches 90% of the adult size. Conclusion We introduce a standardized system to measure and report on different parameters in the EAC. In-office approximated assessments of the isthmus and overall length, using the meatal area, may be invaluable for pre-surgical planning. The near-adult size (90%) of the EAC is reached at 10 years. Introduction The outer ear is formed by the external auditory canal (EAC) and the pinna. The EAC arises from the first and second pharyngeal arches during embryogenesis, while the pinna develops from the hillocks of His. The EAC’s lateral third is fibrocartilaginous, and the medial two-thirds are osseous [1]. The S-shaped EAC starts at the meatus next to the pinna, featuring the isthmus, a narrow bony ring, which is often the entry point of the bony EAC. The annular ring, a shallow bony ridge, attaches the tympanic membrane [2]. Precise EAC measurement—including length, curvature, and anatomical variations—is clinically significant. Limited surgical exposure can impact transmeatal tympanoplasties. Therefore, meatal, isthmic, and annular dimensions must be evaluated before planning transmeatal procedures to ascertain feasibility. Accurate EAC measurements are also crucial in the design of hearing aids, auditory devices, and otologic tools. The EAC changes anatomically from infancy to adulthood. At birth, it mainly consists of cartilage, gradually transforming into bone, radiating laterally from the annular ring during childhood [3]. Studies have recorded key EAC measurements like total length, isthmus width, and canal volume. In adults, the EAC is generally around 25 mm long, with an average isthmus radius of 5.5–6 mm [4]. However, measurements vary considerably, ranging from 19.7 mm to 31.8 mm [5-6]. The isthmus also varies, with dimensions between 6.8 and 8.2 mm in height and 5.2 and 5.7 mm in width [7-8]. Various techniques measure EAC dimensions, including tympanometry, ear prints, 3D scanning, and optical systems [9-11], as well as cadaveric studies and acoustic impedance measurements [12]. Each method depends on different anatomical landmarks, leading to inconsistencies. The medial EAC’s limited accessibility complicates standardization. This variability highlights the need for a standardized technique based on routine clinical practices, like computed tomography (CT) imaging. This study introduces a standardized CT scan method for evaluating EAC dimensions across anatomical planes, providing improved accuracy. Our goal is to examine the EAC’s anatomical changes from infancy through old age, offering a thorough understanding of its developmental evolution. Methods CT scans The study, approved by the Institutional Review Board (IRB), evaluated 163 thin-sliced (1 mm or less) CT scans from patients of diverse ages and both genders. Only individuals with normal external, middle, inner ear, and mastoid air cell systems were included. The exclusion criteria encompassed anatomical anomalies, non-aerated middle ear/mastoid, infections, cholesteatoma, external auditory canal exostoses, pathological lesions, temporal bone fractures, known otologic disorders other than sensorineural hearing loss, and any history of ear surgeries. Areas of interest All measurements were taken on the left ear using the Carestream Vue PACS system, version 12.0. The external auditory canal (EAC) was assessed using three planes: axial, parallel to the EAC, and perpendicular to it. We identified four areas of interest along the EAC. The cartilaginous EAC extends from the pinna (meatus) to the bony canal entry. The bony canal entry is the most lateral point where a complete bony ring appears on a sagittal plane. The meatus is where the EAC has the narrowest diameter on a sagittal plane. The annulus is the most medial point on a sagittal plane with a complete bony ring visible. Measurements All measurements were carried out after verifying each point in three planes (using a three-point location verification system) aligned with the EAC, to ensure the accuracy of the measurements (Fig.1A-C). The axial view was used to measure the curvature of the EAC (Fig.1D). To avoid diagonal measurements, four sagittal views perpendicular to the EAC’s long axis and three coronal views were reformatted (Fig. 2). The reformatted sagittal views were used to calculate surface areas of the four areas of interest. The surface area of the meatus, the bony canal entry, isthmus, and annulus was calculated using the oval formula (πab), with ’a’ as the semi-major axis length and ’b’ as the semi-minor axis length. The coronal views were used to calculate the distances between the different parts of the EAC. Patient consent statement Following the IRB permissions, no patient consent forms were required to conduct the research. Statistical analysis All statistical analyses were performed using IBM SPSS Statistics for Windows, Version 28.0 (IBM Corp, Armonk, NY, USA). A p-value cut-off point of 0.05 at 95% confidence interval (CI) was used to determine statistical significance. Pearson correlation coefficients and linear regression tests were used to assess the age-related differences along the EAC components. Analysis of variance (ANOVA) was used to compare measurements between children and adults by using independent-samples Students T-test. Results Based on inclusion/exclusion criteria, 163 high-resolution temporal bone CT scans were analyzed to measure EAC dimensions. The cohort included 84 males (51%) and 79 females (49%), with a focus on a pediatric population (74%, n=120) under 18 years. The remaining 43 patients were adults. Participant ages ranged from 1 month to 101 years (mean: 15.3 years, median: 5.6 years). The pediatric focus was intentional to assess EAC changes during developmental stages. Results are depicted in Tables 1-2. Changes in Overall EAC Length At birth (0–3 months, n=15), average EAC length was 12.1±1.5 mm, increasing to 19.3±3.8 mm by age 18. The most rapid growth occurred during the first year, reaching 14.1±1.9 mm at 9–12 months (14% increase, p=0.057). By 24 months, the EAC reached 15.5±0.9 mm (10% increase, p=0.2), representing an approximate 30% increase from birth (p<0.001). After 18 years, an additional 4 mm of growth occurred over four to six decades, stabilizing at 23.3 ± 2.5 mm beyond the sixth decade. Age and EAC length showed a strong correlation (r = 0.75, p < 0.001). ). Results are depicted in Tables 1-2 and Fig. 3. Cartilaginous and Bony Segments The cartilaginous EAC measured 8.3±1.7 mm at birth, increasing to 13.1±2.5 mm in individuals over 60 (58% increase). The osseous EAC showed significant growth, measuring 2.5±0.8 mm at birth and expanding to 12.2±1.8 mm by age 50 (490% increase), contributing primarily to overall EAC elongation. Age and cartilaginous-bony junction area showed a strong correlation (r=0.7, p<0.001). During the first two years, ossification was often insufficient, making segment differentiation challenging. Only 41% of children under 24 months exhibited a clear distinction. Among children under 12 months (n = 48), only 3% showed bony ossification, whereas 82% of those aged 12–24 months (n=11) showed ossification evidence. ). Results are depicted in Tables 1-2 and Fig. 3. Meatus Dimensions At birth, meatal height measured 6.6±1.1 mm, reaching 10.3±1.6 mm by 18 years and 13.5±2 mm in individuals over 60. The meatal area expanded from 26.1±8.2 mm² at birth to 270±92 mm² in adults. Age and meatal size showed a strong correlation (r = 0.84, p < 0.001). Results are depicted in Tables 1-2. Isthmus Dimensions At birth, the isthmus was approximately 9 mm from the meatus, extending to 17 mm by age 18. The average adult isthmus area was 122.7±54.2 mm², with adult height, width, and area measuring 8.4 mm, 5.3 mm, and 184.6 mm², respectively. Growth primarily occurred between the cartilaginous-bony junction and the isthmus, while the annulus-isthmus distance remained constant from birth (2.6±0.7 mm) to adulthood (2.8±0.8 mm). Age and isthmus area showed a correlation (r=0.69, p<0.001). Isthmus and meatal areas were highly correlated (r =0.85, p< 0.001). (Fig. 4A). Annulus Dimensions Annular height at birth measured 7.5±0.7 mm, with minimal changes in adulthood (8.8±1.5 mm). Annular width increased from 4.2±1.01 mm at birth to 5.6±1.4 mm in adulthood, demonstrating minimal change over time. EAC Curvature The EAC straightens with age, evident in the axial angle becoming less convex. At birth, the angle was 182.5°±30.1°, compared to 151.3°±13.6° in adults (p=0.001). Age and axial angle had a correlation of r=0.4, p=0.001, with ANOVA confirming significant age-related curvature differences (F=2.273, p=0.02). (Fig 4B). Gender Differences Significant gender-based variations were observed in adult EAC dimensions. Generally, all measurements increased significantly in men. Men had greater EAC length (22.7±3.4 mm) than women (19.7±1.8 mm, p<0.001). Meatal height/width were also increased in men (12.7±2.2 mm, 7.9±1.6 mm) compared to women (10.7±2 mm, 7.3±1.1 mm, p=0.002). The isthmus width was also larger in men (5.5±1 mm) compared to women (4.9±0.9 mm, p=0.04). Results are depicted in Tables 1-2. EAC Maturation Pediatric EAC measurements reached 90% of adult values at varying ages. Overall EAC length (adult: 21.2 mm) reached 90% at 9–12 years (19.6 mm). Isthmus width (adult: 5.1 mm) reached 90% at 6–9 years (4.6 mm). Discussion This study introduces a standardized system for measuring EAC parameters. Key principles include thin-sliced CT scans, reformatted planes aligned with the EAC, and three-plane point-positioning for validation. We defined four key points: meatus, bony canal entry, isthmus, and annular ring. The cartilaginous EAC extends from the meatus to the bony canal entry, defined as the most lateral point with a complete bony ring on a sagittal plane. The meatus is where the EAC has the narrowest diameter, and the annulus is the most medial point with a complete bony ring visible. This system aims to provide a common framework for researchers to communicate and publish findings. We demonstrate the EAC’s evolution from infancy to adulthood. One key finding is that ossification is infrequent in infants during the first year. Another is the relative constancy of tympanic membrane size. The isthmus is located near the annulus, and the bony EAC grows laterally to it during childhood. Correlations exist between meatus/isthmus sizes and meatal height/EAC length, enabling in-office estimation of EAC dimensions by measuring the meatus. The EAC’s contour and size are crucial for sound transmission through air and bone conduction, enhancing mid-range frequencies [13]. They also influence the risk for otitis externa/media, hearing aid fitting, and audiometry accuracy [14-15]. EAC dimensions are critical for transcanal otologic surgeries. The narrow EAC serves as the surgical conduit, especially in endoscopic procedures [16]. Anatomical changes during childhood impact ear surgery. Children have shorter, straighter EACs, favoring some approaches but limiting instrumentation. The opposite is true in adults. Suboptimal EACs can challenge intracanal surgeries, requiring careful planning [17]. In our study, we measured the EAC along its different sections. At birth, the overall EAC length was 12.1 ± 1.5 mm, reaching an average adult size of 21.2 mm. It is essential to note that the EAC continues to grow steadily until approximately 60 years of age. By the 7th decade of life, the EAC doubles in length compared to birth, reaching 23.3 ± 2.5 mm. The width of the EAC varies across different sections, with the meatus being the largest, followed by the annulus, and the isthmus being the smallest in width (mm) and area sizes (mm2). At birth, meatal width was 4.96 mm, reaching an average adult size of 7.6 mm. Unlike the overall length, meatal width continues to expand even after the 7th decade of life, reaching up to 8.3 mm. Notably, the EAC lengths measured in this study were smaller than the common consensus regarding the adult EAC being 25 mm long and 8 mm in diameter [18-19]. At 18 years, the total EAC length was significantly smaller (19.3 ± 3.8 mm). Ossification of the bony EAC begins between 16 and 23 weeks of gestation and continues postnatally [20-21]. Distinguishing cartilaginous and bony parts can be difficult early in childhood. Most EAC growth occurs in the first two years, increasing length by approximately 30%, primarily in the bony part lateral to the isthmus. In our study, only 18% of children in their second year showed no ossification on CT scans, compared to 97% in their first year (p<0.001). In adults, the isthmus is located in the bony EAC, approximately 5.9 ± 2 mm medial to the cartilaginous-bony junction, remaining near the annulus (2.38 ± 1.2 mm). It is not located at the osseous-cartilaginous junction. In adults, average isthmic height and width were 8.43 ± 1.2 mm and 5.3 ± 1.4 mm at 18 years. El-Anwar et al.’s study reported smaller EAC height/width measurements, potentially due to differing techniques [22]. Our measurements, aligned with the EAC axis, aimed for greater accuracy. As the narrowest part of the EAC, the exact dimensions of the isthmus determine the surgeon’s ability to operate via this corridor (trans-meatal microscopic and/or endoscopic surgeries). A newborn has an average isthmic width of 3.4 ± 1.1 mm, which increases to an average of 5.3 ± 1 mm in adulthood. According to Ito et al. [23], to safely introduce a rigid endoscope into the EAC, there should be a gap greater than 0.5 mm between the endoscope and the inner canal wall of the EAC. They recommend using a narrow 2.7 mm-diameter endoscope during pediatric myringoplasty only when the diameter of the EAC in its narrowest part exceeds 3.2 mm. In adults, an EAC smaller than 4 mm in diameter in its narrowest part is considered a narrow EAC. Lou [24] recommends using a 4.0 mm-diameter rigid endoscope in patients over 16 years of age. Our study results suggest that in the 9-12 year age group, isthmic width of 5.6 ± 0.6 mm should enable safe use of the 4.0 mm-diameter rigid endoscope in patients aged 9-12 years and older. Though visible through the meatus, the isthmus cannot be easily measured in-office due to EAC curvature. Our study showed a strong correlation between isthmus and meatal areas, enabling simple, non-invasive isthmus assessment via meatal measurement. This could improve hearing aid fitting for online orders, allowing users to self-assess at home. The curvature of the EAC on axial images changes significantly with age, being relatively flat in newborns (182°) and becoming curvier with age (150°). Measurement differences exist between genders, with women generally having smaller EAC measurements. Conclusion This standardized system provides a novel approach to measuring EAC components, employing thin-section CT imaging, EAC-aligned reformatted planes, and three-dimensional point-positioning for enhanced accuracy and validation. These measurements hold significant potential for implementation in pre-surgical planning for otologic interventions and in the precise customization of hearing aids. Additionally, identified correlations between EAC regions enable the development of approximate in-office assessment techniques. Practitioner Points: • Infant EACs exhibit limited ossification in the first year; bony growth in childhood primarily occurs lateral to the isthmus. • The isthmus maintains a consistent proximity to the annulus throughout development. • Strong correlations between meatal/isthmus sizes and meatal height/EAC length enable simple, in-office estimation of EAC dimensions. References 1. Eckerdal O, Ahlqvist J, Alehagen U, Wing K. Length dimensions and morphologic variations of the external bony auditory canal. A radiographic and histologic investigation. Dentomaxillofac Radiol. 1978;7(1):43-50. 2. Mozaffari M, Nash R, Tucker AS. Anatomy and Development of the Mammalian External Auditory Canal: Implications for Understanding Canal Disease and Deformity. Front Cell Dev Biol. 2021;8:617354. 3. Ikari Y, Katori Y, Ohtsuka A, et al. Fetal development and variations in the cartilages surrounding the human external acoustic meatus. Ann Anat. 2013;195(2):128-36. 4. Areias B, Santos C, Natal JRM, Gentil F, Parente MPL. Finite element modelling of sound transmission from outer to inner ear. Proc Inst Mech Eng H. 2016;230(11):999–1007. 5. Rasetshwane DM, Neely ST. Inverse solution of ear-canal area function from reflectance. J Acoust Soc Am . 2011;130(6):3873–81. 6. Chan J, Geisler C. Estimation of eardrum acoustic pressure and of ear canal length from remote points in the canal. J Acoust Soc Am. 1990;87(3):1237–47. 7. Li CL, Li J, Guo Y, Zhang TY. Measurement method for external auditory canal and clinical application in congenital aural stenosis. Int J Pediatr Otorhinolaryngol. 2020;137:110233. 8. Ahmad I, Lee WC, Binnington JD. External auditory canal measurements: localization of the isthmus. Otorhinolaryngol Nova. 2000;10(5):183–6. 9. Meijerman L, van der Lugt C, Maat GJ. Cross-sectional anthropometric study of the external ear. J Forensic Sci. 2007;52(2):286-93. 10. Fan H, Yu S, Wang M, et al. Analysis of the external acoustic meatus for ergonomic design: Part I - Measurement of the external acoustic meatus using casting, scanning, and rapid estimation approaches. Ergonomics. 2021;64(5):640-56. 11. Hennig L, Krüger M, Bülow R, et al. Morphology and anatomical variability of the external auditory canal: A population-based MRI study. Ann Anat. 2025;257:152319. 12. Voss SE, Horton NJ, Fairbank KE, Xia L, Tinglin LRK, Girardin KD. Measurements of ear-canal cross-sectional areas from live human ears with implications for wideband acoustic immittance measurements. J Acoust Soc Am . 2020;148(5):3042. 13. Keefe DH, Porter HL, Fitzpatrick DF. Shape and sound analyses of the human ear-canal geometrya). J Acoust Soc Am . 2025;157(5):3638-54. 14. van Spronsen E, Geerse S, Mirck PGB, van der Baan S, Fokkens WJ, Ebbens FA. The shape of the osseous external auditory canal and its relationship to chronic external otitis. Otol Neurotol. 2014;35(10):1790–6. 15. Lee YF, Wei PY, Chu CH, Liao WH, Shiao AS, Wang MC. A Retrospective Study to Identify the Relationship Between the Dimension of Osseous External Auditory Canal and Chronic Otitis Media. Ear Nose Throat J. 2020;99(8):532-6. 16. Ayache S, Beltran M, Guevara N. Endoscopic classification of the external auditory canal for transcanal endoscopic ear surgery. Eur Ann Otorhinolaryngol Head Neck Dis. 2019;136(4):247-50. 17. Sun WH, Kuo CL, Huang TC. The anatomic applicability of transcanal endoscopic ear surgery in children. Int J Pediatr Otorhinolaryngol. 2018;105:118-122. 18. Grewe J, Thiele C, Mojallal H, et al. New HRCT-based measurement of the human outer ear canal as a basis for acoustical methods. Am J Audiol. 2013;22(1):65-73. 19. Balouch AP, Bekhazi K, Durkee HE, et al. Measurements of ear-canal geometry from high-resolution CT scans of human adult ears. Hear Res. 2023;434:108782. 20. Juliano AF. Cross sectional imaging of the ear and temporal bone. Head Neck Pathol. 2018;12(3):302–20. 21. Manni JJ, Berénos-Riley LC. Ossification of the external ear: a case report and review of the literature. Eur Arch Otorhinolaryngol. 2005;262(12):961-4. 22. El-Anwar MW, Fouad YA, Elgohary AF, Saber S, Mobasher MA. External Auditory Canal: Computed Tomography Analysis and Classification. Int Arch Otorhinolaryngol. 2023;27(4):e565-e570. 23. Ito T, Kubota T, Watanabe T, Futai K, Furukawa T, Kakehata S. Transcanal endoscopic ear surgery for pediatric population with a narrow external auditory canal. Int J Pediatr Otorhinolaryngol. 2015;79(12):2265-9. 24. Lou Z. The outer diameter of the endoscope is important when performing endoscopic transcanal myringoplasty. Braz J Otorhinolaryngol. 2017;83(6):730-1. Legends to tables and figures: • Table 1- External auditory canal measurements in men by age group. Length is measured in millimeters (mm), surface area in mm 2 • Table 2- External auditory canal measurements in women by age group. Length is measured in millimeters (mm), surface area in mm 2 • Figure 1- Point-location verification system using CT scans in three planes reformatted to align with the EAC. A-axial view, B- coronal view, C- sagittal view, D- Axial view: The curvature of the bony EAC was assessed by measuring the angle created between the medial part of the bony EAC and its lateral part. Three positioning points were set. The medial point was set at the center of the bony EAC near the tympanic membrane. The middle point was set at the level of the isthmus, and the lateral point at the meatus. Figure 2- Areas of interest in reformatted Sagittal, Coronal and Axial views. The four points of interest: the meatus (A), the entry to the bony canal (B), the isthmus (C), and the annulus (D) are displayed on all three reformatted planes: upper row sagittal view, second row coronal view, bottom row axial view. The use of three different planes to validate point location improved the accuracy of the measurements. The cartilaginous EAC extends from the pinna (meatus) to the bony canal entry. The bony canal entry is the most lateral point where a complete bony ring appears on a sagittal plane. The meatus is where the EAC has the narrowest diameter on a sagittal plane. The annulus is the most medial point on a sagittal plane with a complete bony ring visible. Reformatted sagittal views were used to calculate the surface areas of the four points of interest, by using the oval formula (πab), with ’a’ as the semi-major axis length and ’b’ as the semi-minor axis length. Reformatted coronal views were used to calculate the distances in millimeters (mm) between the meatus to the entry of the bony EAC, from the entry of the bony EAC and the isthmus and from the isthmus to the tympanic membrane. Lines intersect the four points of interest respectively. Figure 3- Changes in bony, cartilaginous, and overall size of the EAC (scatter plot) The bony part elongates significantly as the person ages, compared to the cartilaginous part. At birth (0-3 months, n=15), the average overall EAC was measured at 12.1±1.5 mm, reaching to 19.3 ± 3.8 mm at the age of 18 (n=10). The most significant growth occurred during the first year of life, with the EAC reaching 14.1±1.9 mm at 9-12 months (14% increase in length, p=0.057). After 18 years, the EAC continued to grow an additional 4 mm overall in the following 4-6 th decades, reaching the average of 23.3±2.5 mm. Figure 4- Linear regression analysis A- Linear regression analysis that assesses relations between meatal and isthmic areas (mm 2 ). A strong correlation was evident (r=0.85, p<0.001). B- Linear regression analysis that assesses relations between age (months) and the axial angle of the bony external auditory canal (EAC). (Pearson correlation coefficient r=0.4, p=0.001). Supplementary Material File (table 1 rr.docx) Download 45.13 KB File (table 2 rr.docx) Download 45.17 KB Information & Authors Information Version history V1 Version 1 15 July 2025 Copyright This work is licensed under a Non Exclusive No Reuse License. Authors Affiliations Ofir Zavdy 0000-0002-4381-216X [email protected] Rabin Medical Center View all articles by this author Lirit Levi Rabin Medical Center View all articles by this author meirav sokolov Rabin Medical Center View all articles by this author Hanna Kabatiansky Ariel University School of Communication View all articles by this author Daniella Fadida Ariel University School of Communication View all articles by this author Eyal Yosefof 0000-0001-8211-9774 Rabin Medical Center View all articles by this author Leah Fostick Ariel University School of Communication View all articles by this author Ohad Hilly Rabin Medical Center View all articles by this author Metrics & Citations Metrics Article Usage 358 views 175 downloads .FvxKWukQNSOunydq8rnd { width: 100px; } Citations Download citation Ofir Zavdy, Lirit Levi, meirav sokolov, et al. Research Article Tomography-aided Anthropometric Measurements of External Auditory Canal from Birth to Adulthood. Authorea . 15 July 2025. 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