Computed Tomography-Derived Normative Values and Physiologic Asymmetry of the Bony Nasolacrimal Duct in Adults

Computed Tomography-Derived Normative Values and Physiologic Asymmetry of the Bony Nasolacrimal Duct in Adults | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Computed Tomography-Derived Normative Values and Physiologic Asymmetry of the Bony Nasolacrimal Duct in Adults Mohamed Ragab Nouh, Saleh Kamal Alzahrani, Islam Salah Mourad, and 1 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-9118039/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 7 You are reading this latest preprint version Abstract Purpose To establish the first multi-dimensional, percentile-based CT normative reference values for the bony nasolacrimal duct (NLD) in a large non-surgical adult cohort, and to define 95th-percentile thresholds for physiologic inter-ocular asymmetry. Materials and Methods In this retrospective study of 200 adults (mean age, 41.2 ± 13.6 years; 52% female), two blinded radiologists at two independent sites measured anteroposterior (AP) diameter, transverse width, and cross-sectional area bilaterally at a standardized axial landmark (maxillary sinus infundibulum). Cross-sectional area was calculated from the linear diameters, assuming an elliptical cross-section. Reliability was assessed using intraclass correlation coefficients (ICC) and Bland–Altman analysis. Normative percentiles and 95th-percentile asymmetry thresholds were derived. Results Mean bilateral values were comparable: AP diameter 8.0–8.1 ± 2.0–2.1 mm, transverse width 5.1–5.2 ± 0.8–0.9 mm, and cross-sectional area 32.8–33.1 ± 9.4–9.7 mm². The 2.5–97.5th percentile ranges were 5.0–13.0 mm for AP diameter, 4.0–7.0 mm for transverse width, and 15.7–61.3 mm² for cross-sectional area. Physiologic asymmetry was small: median Δ diameter, width, and area were 1.0 mm, 0 mm, and 3.9 mm², respectively. The 95th percentile cutoffs for asymmetry were 4.0 mm, 2.0 mm, and 23.7 mm², respectively. Intra-reader ICCs ranged from 0.88–0.93, with Bland-Altman bias < 0.2 mm for diameters and < 1.0 mm² for area. Conclusion This study presents the first multi-dimensional, percentile-based CT normative reference for the adult bony nasolacrimal duct from a large non-surgical cohort, including validated 95th-percentile asymmetry thresholds for clinical reporting and pre-procedural surgical planning. Nasolacrimal duct CT imaging Normative values Interocular asymmetry Reliability Preoperative planning Figures Figure 1 Figure 2 Introduction The nasolacrimal duct (NLD) is a critical bony conduit for physiologic tear drainage, and its obstruction is a leading cause of epiphora (excessive tearing) [ 1 , 2 ]. Primary acquired nasolacrimal duct obstruction (PANDO) is a common condition, with congenitally narrow bony anatomy increasingly recognized as a predisposing factor [ 1 – 3 ]. Pre-procedural evaluation of the NLD is essential for diagnosing obstruction, planning dacryocystorhinostomy (DCR), and avoiding iatrogenic injury during sinonasal surgery [ 4 , 5 ]. CT is the imaging modality of choice for this purpose, offering high-resolution depiction of bony anatomy, rapid acquisition, and broad availability [ 4 , 6 ]. Despite this clinical importance, no large-cohort study has established percentile-based normative values for multi-dimensional bony NLD measurements in a non-surgical adult population, nor has any prior work defined quantitative inter-ocular asymmetry thresholds. Existing studies are constrained by small sample sizes, heterogeneous populations, or a primary focus on surgical patients [ 6 – 10 ]. Therefore, the purpose of this study was to establish multi-dimensional, percentile-based CT normative reference values for the bony NLD in a large non-surgical adult cohort, and to define the 95th-percentile threshold for physiologic inter-ocular asymmetry — two benchmarks that are currently absent from the radiology literature and directly required for standardized reporting and pre-procedural planning Methods Study Design and Patient Selection This retrospective institutional review board-approved study (with a waiver of informed consent) included consecutive adult patients (≥ 18 years) who underwent non-contrast paranasal sinus CT at two adjacent hospital sites between January and June 2025. Clinical indications included suspected sinusitis, preoperative planning for septoplasty or non-lacrimal sinus surgery, and trauma evaluation. The patient population was representative of the multi-ethnic urban demographic characteristic of the Arabian Gulf region, comprising individuals of Arab, South Asian, and other diverse ethnic backgrounds. Exclusion criteria were prior sinonasal or lacrimal surgery, significant maxillofacial pathology (e.g., polyposis, mucocele, invasive tumor), fractures involving the lacrimal or maxillary bones, or technically inadequate scans. The final cohort comprised 200 unique patients (400 sides), with 100 patients contributed from each site. CT Acquisition Protocol All examinations were performed using a standardized paranasal sinus CT protocol on 128–detector row CT scanners (Revolution EVO; GE Healthcare) at both sites. Acquisition parameters were harmonized to ensure reproducibility: tube voltage, 120 kV; automatic tube current modulation (reference, 150 mAs); collimation, 0.6 mm; and pitch, 0.8. Axial images were reconstructed at a 0.625-mm slice thickness with a 0.3-mm increment using a high-spatial-frequency (bone) algorithm. All images were reviewed on a dedicated PACS workstation (Vue PACS; Carestream Health, Phillips, the Netherlands), consistent with the routine clinical workflow at both institutions. Image Analysis and Measurements Two blinded radiologists, one at each site, independently analyzed their respective 100 patients. Measurements were performed on axial source images at a standardized osseous landmark: the level of the maxillary sinus infundibulum. This landmark was selected to provide a simple, reproducible, and clinically applicable reference point. At this level, the maximum internal anteroposterior (AP) diameter, transverse width, and cross-sectional area of the bony NLD were measured bilaterally. The cross-sectional area was subsequently calculated assuming an elliptical shape using the formula: Area = π × (AP diameter/2) × (width/2). This efficient calculation was chosen to reflect a practical clinical workflow in which complex manual segmentation is often not feasible. Figure 1 illustrates the measurement technique. For intra-reader reliability, each radiologist re-measured a randomly selected subset of 50 patients (100 sides) after a 6-week washout period, blinded to their initial results. Reliability and Statistical Analysis Inter-observer reliability was evaluated by comparing the pooled measurements from the two independent readers using intraclass correlation coefficients (ICC, two-way random-effects, absolute agreement, single measure). An ICC ≥ 0.80 was prespecified as indicating excellent reliability. Intra-reader reliability was assessed using repeated measurements and quantified with ICCs and Bland-Altman analysis (to assess reporting bias and 95% limits of agreement). The proportion of repeat measures falling within predefined clinical tolerance limits (± 1 mm for diameters, ± 2 mm² for area) was calculated. Statistical analyses were performed using R software, version 4.2.0. Continuous variables are reported as mean ± standard deviation and as percentiles. Side-to-side differences were analyzed using paired t-tests. Bootstrap resampling (2,000 iterations) was used to derive confidence intervals for extreme percentiles (2.5th and 97.5th) and the asymmetry cutoff (95th percentile). A p-value < 0.05 was considered statistically significant. Results Study Cohort A total of 200 adult patients (400 sides) were included. The mean age was 41.2 ± 13.6 years (range, 18–72 years); 52% were female. All CT examinations were technically adequate, and bilateral NLD measurements were successfully obtained in every case. Normative Values NLD dimensions demonstrated narrow bilateral distributions, with comparable right- and left-sided values (Fig. 2). All cross-sectional area values are derived from direct diameter measurements. Percentile ranges confirmed reproducible reference values across the cohort. A site-stratified analysis showed no significant differences, supporting pooled reporting. Physiological Inter-Ocular Asymmetry Absolute side-to-side differences in NLD dimensions were small, indicating minimal physiologic asymmetry across the cohort. The median inter-ocular difference was 1.0 mm for AP diameter, 0.0 mm for transverse width, and 3.9 mm² for cross-sectional area. A median of 0.0 mm indicates that the most common finding was perfect symmetry, although the 95th-percentile cutoff indicates that a range of normal variation exists (Table 1 ). These thresholds were 4.0 mm for the AP diameter, 2.0 mm for the transverse width, and 23.7 mm² for the cross-sectional area. Asymmetry exceeding these cutoffs is therefore uncommon in a healthy population and may warrant further clinical consideration. Table 1 Physiological Inter-Ocular Asymmetry (n = 200 patients) Metric Mean ± SD Median (IQR) 95th percentile cutoff Prevalence > 2 mm (%, 95% CI) Δ AP diameter (mm) 0.96 ± 1.1 1.0 (0–2) 4.0 5% (95% CI ~ 2–8) Δ Width (mm) 0.42 ± 0.6 0.0 (0–1) 2.0 3% (95% CI ~ 1–6) Δ Area (mm²) 6.2 ± 7.8 3.9 (0–9) 23.7 4% (95% CI ~ 2–7) Δ = absolute side-to-side difference. Reliability Repeat measurements demonstrated excellent reproducibility (Table 2 ). Inter-observer ICCs exceeded 0.88 across all metrics, and intra-reader Bland–Altman analysis showed negligible bias with limits of agreement within predefined tolerance thresholds. More than 85% of repeat measures fell within tolerance limits, confirming the robustness, site comparability, and reader reproducibility necessary for clinical application across different institutions. Table 2 Intra-Reader Reliability (Repeat Subset, n = 50 per reader) Metric Inter-Observer ICC (95% CI) Intra-Reader ICC (95% CI)* Bland-Altman 95% Limits of Agreement AP Diameter (mm) 0.91 (0.88–0.94) 0.91 (0.85–0.95) −1.9 to + 2.1 mm Transverse Width (mm) 0.89 (0.86–0.92) 0.89 (0.82–0.93) −1.6 to + 1.4 mm Cross-Sectional Area (mm²) 0.93 (0.90–0.95) 0.93 (0.87–0.96) −13.4 to + 11.3 mm² *ICC = intraclass correlation coefficient. *Pooled intra-reader estimates from Readers 1 & 2. Discussion This study provides reproducible CT-derived normative reference values for the adult bony nasolacrimal duct, together with percentile-based thresholds for physiologic inter-ocular asymmetry. Our principal findings are that NLD dimensions exhibit consistent bilateral distributions and that minor asymmetry is common, whereas significant asymmetry is rare. By defining percentile cutoffs, we establish objective standards for radiologists to distinguish normal anatomic variation from pathologic narrowing. Furthermore, deriving these values from a multi-ethnic urban cohort enhances their generalizability across diverse populations. Our results expand on previous smaller studies [ 5 , 9 – 12 ] — which were often limited to single readers without rigorous reliability assessment — by providing percentile distributions, robust multi-reader reproducibility metrics, and defined asymmetry thresholds across a substantial cohort. The high intraclass correlation coefficients and narrow Bland–Altman limits confirm that standardized axial measurements at the maxillary infundibulum are reliable across both sites and independent readers. Furthermore, unlike prior studies that relied on multiplanar reformations or measurements along the duct’s full course [ 10 – 12 ], we intentionally prioritized clinical utility by standardizing a simple measurement at a single, reproducible axial landmark. This approach, using direct PACS tools on standard source images, seamlessly integrates into the radiologist’s existing workflow, thereby enhancing both the practical adoption and the methodological rigor of these normative values. Consequently, while previous research [ 3 , 7 , 11 – 14 ] has primarily focused on describing anatomic differences in patients with established PANDO, our work provides the foundational normative data required to objectively define a narrow bony canal as a potential contributing cause. The clinical implications are twofold. First, an AP diameter below the 2.5th percentile (≈ 5.0 mm) provides an objective definition for a congenitally narrow canal, which is a suspected risk factor for primary acquired nasolacrimal duct obstruction (PANDO) [ 1 , 2 ]. Second, the demonstration of frequent but bounded asymmetry underscores the need for bilateral evaluation, particularly in patients undergoing surgery or presenting with unilateral symptoms. The defined 95th-percentile cutoffs (e.g., > 4 mm for AP diameter) provide a quantitative framework for flagging a duct as disproportionately narrow relative to the contralateral side, which could be the underlying substrate for unilateral epiphora. Several considerations temper these findings. The retrospective design limited the ability to correlate with clinical outcomes, and only bony anatomy was assessed; mucosal and soft-tissue components, which also influence obstruction, were beyond the scope of this study. Our methodology, which uses direct linear measurements and a straightforward elliptical-area calculation, was designed to integrate seamlessly into routine radiological practice without specialized software; nevertheless, residual interindividual variability underscores the role for future automated segmentation and deep learning approaches to improve efficiency and scalability [ 15 ]. Future studies should link these morphometric data to clinical outcomes, such as surgical success in dacryocystorhinostomy, to assess their prognostic value. Conclusion This study presents the first multi-dimensional, percentile-based CT normative reference for the adult bony nasolacrimal duct, derived from a large non-surgical cohort, and establishes evidence-based 95th-percentile thresholds for physiologic inter-ocular asymmetry. Validated across two sites and two independent readers, these benchmarks provide immediately applicable standards for distinguishing normal anatomy from pathologic narrowing, characterizing unilateral asymmetry, and guiding pre-procedural planning in sinonasal and lacrimal surgery. Declarations Author Contribution Mohamed Ragab Nouh — Guarantor of the integrity of the entire study; contributed to study conception and design; performed literature research; participated in clinical studies; conducted data analysis; contributed to manuscript preparation; performed manuscript editing. Saleh Kamal Alzahrani — Contributed to study conception and design; performed literature research; contributed to manuscript preparation; performed manuscript editing. Islam Salah Mourad — Participated in clinical studies; performed literature research; contributed to manuscript preparation. Mostafa Magdy Donia — Performed literature research; participated in clinical studies; contributed to manuscript preparation. Conflict of Interest. The authors declare no conflicts of interest. Funding Declaration. The authors received no financial support for this research. Human Ethics and Consent to Participate. Institutional review board approval was obtained, and informed consent was waived due to the retrospective design and use of anonymized data. References Ali MJ, Paulsen F (2019) Etiopathogenesis of Primary Acquired Nasolacrimal Duct Obstruction: What We Know and What We Need to Know. Ophthalmic Plast Reconstr Surg 35:426–433. https://doi.org/10.1097/IOP.0000000000001310 Ali MJ (2023) Etiopathogenesis of primary acquired nasolacrimal duct obstruction (PANDO). Prog Retin Eye Res 96:101193. https://doi.org/10.1016/j.preteyeres.2023.101193 Yang MK, Sa H-S, Kim N et al (2022) Bony nasolacrimal duct size and outcomes of nasolacrimal silicone intubation for incomplete primary acquired nasolacrimal duct obstruction. PLoS ONE 17:e0266040. https://doi.org/10.1371/journal.pone.0266040 Papathanassiou S, Koch T, Suhling MC et al (2019) Computed Tomography Versus Dacryocystography for the Evaluation of the Nasolacrimal Duct-A Study With 72 Patients. Laryngoscope Investig Otolaryngol 4:393–398. https://doi.org/10.1002/lio2.293 Lin Z, Kamath N, Malik A (2021) Morphometric differences in normal bony nasolacrimal anatomy: comparison between four ethnic groups. Surg Radiol Anat 43:179–185. https://doi.org/10.1007/s00276-020-02614-4 Choi SC, Lee S, Choi HS et al (2016) Preoperative Computed Tomography Findings for Patients with Nasolacrimal Duct Obstruction or Stenosis. Korean J Ophthalmol 30:243–250. https://doi.org/10.3341/kjo.2016.30.4.243 Janssen AG, Mansour K, Bos JJ, Castelijns JA (2001) Diameter of the bony lacrimal canal: normal values and values related to nasolacrimal duct obstruction: assessment with CT. AJNR Am J Neuroradiol 22:845–850 McCormick A, Sloan B (2009) The diameter of the nasolacrimal canal measured by computed tomography: gender and racial differences. Clin Exp Ophthalmol 37:357–361. https://doi.org/10.1111/j.1442-9071.2009.02042.x Lee H, Ha S, Lee Y et al (2012) Anatomical and morphometric study of the bony nasolacrimal canal using computed tomography. Ophthalmologica 227:153–159. https://doi.org/10.1159/000331986 Park J-H, Huh J-A, Piao J-F et al (2019) Measuring nasolacrimal duct volume using computed tomography images in nasolacrimal duct obstruction patients in Korean. Int J Ophthalmol 12:100–105. https://doi.org/10.18240/ijo.2019.01.16 Su P-Y, Wang J-K, Chang S-W (2023) Computed Tomography Morphology of Affected versus Unaffected Sides in Patients with Unilateral Primary Acquired Nasolacrimal Duct Obstruction. J Clin Med 12:340. https://doi.org/10.3390/jcm12010340 Wang W, Gong L, Wang Y (2022) Anatomic characteristics of primary acquired nasolacrimal duct obstruction: a comparative computed tomography study. Quant Imaging Med Surg 12:5068–5079. https://doi.org/10.21037/qims-22-170 Takahashi Y, Nakata K, Miyazaki H et al (2014) Comparison of bony nasolacrimal canal narrowing with or without primary acquired nasolacrimal duct obstruction in a Japanese population. Ophthalmic Plast Reconstr Surg 30:434–438. https://doi.org/10.1097/IOP.0000000000000238 Sun J, Gan L, Qian J, Ren H (2025) Computed tomography assessment of the narrowest bony nasolacrimal canal diameter with and without primary acquired nasolacrimal duct obstruction: a comparative study of the Chinese population. Int Ophthalmol 45:140. https://doi.org/10.1007/s10792-025-03516-3 Haylaz E, Gumussoy I, Duman SB et al (2025) Automatic Segmentation of the Nasolacrimal Canal: Application of the nnU-Net v2 Model in CBCT Imaging. J Clin Med 14:778. https://doi.org/10.3390/jcm14030778 Additional Declarations No competing interests reported. Supplementary Files FinalTables.docx Cite Share Download PDF Status: Under Review Version 1 posted Reviews received at journal 05 May, 2026 Reviewers agreed at journal 26 Apr, 2026 Reviewers agreed at journal 26 Apr, 2026 Reviewers invited by journal 21 Apr, 2026 Editor assigned by journal 19 Mar, 2026 Submission checks completed at journal 17 Mar, 2026 First submitted to journal 13 Mar, 2026 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-9118039","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":629777898,"identity":"dc159bbb-89e3-4766-bce6-14753c602e87","order_by":0,"name":"Mohamed Ragab Nouh","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAzElEQVRIiWNgGAWjYLACxob/dvwMDGwkaWFOlmwgVQvjhgPEatGdffjxi5872JiNbyQ/e/ChgkGeX+wAfi1m59LMLHvP8PCZ3UgzN5xxhsFw5uwEAlrOMJgZ8LZJMJvdSDCT5m1jSDC4TVAL+zfDv20GjJtnpH8jVguP8WPetgTGDRI5RNvCU8Yse+ZAssSZN2WSM85IEOMX9s0f3+44YMffnr5N4kOFjTy/NAEtQMAmAaYEwColCCoHAeYPYIr/AFGqR8EoGAWjYAQCAIOnQ4w8AwVrAAAAAElFTkSuQmCC","orcid":"","institution":"Alexandria University","correspondingAuthor":true,"prefix":"","firstName":"Mohamed","middleName":"Ragab","lastName":"Nouh","suffix":""},{"id":629777900,"identity":"9aca4e1d-0497-4ba0-b448-36063c0fbdfa","order_by":1,"name":"Saleh Kamal Alzahrani","email":"","orcid":"","institution":"King Fahd Military Medical Complex","correspondingAuthor":false,"prefix":"","firstName":"Saleh","middleName":"Kamal","lastName":"Alzahrani","suffix":""},{"id":629777902,"identity":"cba0ffcc-2c2a-430e-b643-614de79e42e1","order_by":2,"name":"Islam Salah Mourad","email":"","orcid":"","institution":"King Fahd Military Medical Complex","correspondingAuthor":false,"prefix":"","firstName":"Islam","middleName":"Salah","lastName":"Mourad","suffix":""},{"id":629777903,"identity":"4af15c64-f332-4eb9-ab42-9c4ba7b96fdf","order_by":3,"name":"Mostafa Magdy Donia","email":"","orcid":"","institution":"Alexandria University","correspondingAuthor":false,"prefix":"","firstName":"Mostafa","middleName":"Magdy","lastName":"Donia","suffix":""}],"badges":[],"createdAt":"2026-03-13 20:53:59","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-9118039/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-9118039/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":108385111,"identity":"94e41b77-f5e6-4081-9a27-0248d0cc4a91","added_by":"auto","created_at":"2026-05-04 06:01:24","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":292916,"visible":true,"origin":"","legend":"\u003cp\u003eLegend not included with this version.\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-9118039/v1/751cc7f01e31353f58ff0ca5.png"},{"id":108385112,"identity":"c48bb41d-071d-48e2-98a3-374c7329f492","added_by":"auto","created_at":"2026-05-04 06:01:24","extension":"jpg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":121867,"visible":true,"origin":"","legend":"\u003cp\u003eLegend not included with this version.\u003c/p\u003e","description":"","filename":"Figure2Plot.jpg","url":"https://assets-eu.researchsquare.com/files/rs-9118039/v1/74e5d6c04b6128776e65a6fb.jpg"},{"id":108804399,"identity":"df78cd5a-5d51-444b-81fc-27752b08efa9","added_by":"auto","created_at":"2026-05-08 15:20:12","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":671109,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-9118039/v1/47f18db9-8093-4716-bbe6-3e418a0aa638.pdf"},{"id":108385110,"identity":"c63a3dae-66d9-407e-b6f2-22cb1b3db3d3","added_by":"auto","created_at":"2026-05-04 06:01:24","extension":"docx","order_by":0,"title":"","display":"","copyAsset":false,"role":"supplement","size":15802,"visible":true,"origin":"","legend":"","description":"","filename":"FinalTables.docx","url":"https://assets-eu.researchsquare.com/files/rs-9118039/v1/4d30aff14b8b795f1f86727a.docx"}],"financialInterests":"No competing interests reported.","formattedTitle":"Computed Tomography-Derived Normative Values and Physiologic Asymmetry of the Bony Nasolacrimal Duct in Adults","fulltext":[{"header":"Introduction","content":"\u003cp\u003eThe nasolacrimal duct (NLD) is a critical bony conduit for physiologic tear drainage, and its obstruction is a leading cause of epiphora (excessive tearing) [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. Primary acquired nasolacrimal duct obstruction (PANDO) is a common condition, with congenitally narrow bony anatomy increasingly recognized as a predisposing factor [\u003cspan additionalcitationids=\"CR2\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e].\u003c/p\u003e \u003cp\u003ePre-procedural evaluation of the NLD is essential for diagnosing obstruction, planning dacryocystorhinostomy (DCR), and avoiding iatrogenic injury during sinonasal surgery [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e, \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]. CT is the imaging modality of choice for this purpose, offering high-resolution depiction of bony anatomy, rapid acquisition, and broad availability [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e, \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eDespite this clinical importance, no large-cohort study has established percentile-based normative values for multi-dimensional bony NLD measurements in a non-surgical adult population, nor has any prior work defined quantitative inter-ocular asymmetry thresholds. Existing studies are constrained by small sample sizes, heterogeneous populations, or a primary focus on surgical patients [\u003cspan additionalcitationids=\"CR7 CR8 CR9\" citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eTherefore, the purpose of this study was to establish multi-dimensional, percentile-based CT normative reference values for the bony NLD in a large non-surgical adult cohort, and to define the 95th-percentile threshold for physiologic inter-ocular asymmetry \u0026mdash; two benchmarks that are currently absent from the radiology literature and directly required for standardized reporting and pre-procedural planning\u003c/p\u003e"},{"header":"Methods","content":"\u003cp\u003eStudy Design and Patient Selection\u003c/p\u003e \u003cp\u003eThis retrospective institutional review board-approved study (with a waiver of informed consent) included consecutive adult patients (\u0026ge;\u0026thinsp;18 years) who underwent non-contrast paranasal sinus CT at two adjacent hospital sites between January and June 2025. Clinical indications included suspected sinusitis, preoperative planning for septoplasty or non-lacrimal sinus surgery, and trauma evaluation. The patient population was representative of the multi-ethnic urban demographic characteristic of the Arabian Gulf region, comprising individuals of Arab, South Asian, and other diverse ethnic backgrounds.\u003c/p\u003e \u003cp\u003eExclusion criteria were prior sinonasal or lacrimal surgery, significant maxillofacial pathology (e.g., polyposis, mucocele, invasive tumor), fractures involving the lacrimal or maxillary bones, or technically inadequate scans. The final cohort comprised 200 unique patients (400 sides), with 100 patients contributed from each site.\u003c/p\u003e \u003cp\u003eCT Acquisition Protocol\u003c/p\u003e \u003cp\u003eAll examinations were performed using a standardized paranasal sinus CT protocol on 128\u0026ndash;detector row CT scanners (Revolution EVO; GE Healthcare) at both sites. Acquisition parameters were harmonized to ensure reproducibility: tube voltage, 120 kV; automatic tube current modulation (reference, 150 mAs); collimation, 0.6 mm; and pitch, 0.8. Axial images were reconstructed at a 0.625-mm slice thickness with a 0.3-mm increment using a high-spatial-frequency (bone) algorithm. All images were reviewed on a dedicated PACS workstation (Vue PACS; Carestream Health, Phillips, the Netherlands), consistent with the routine clinical workflow at both institutions.\u003c/p\u003e \u003cp\u003eImage Analysis and Measurements\u003c/p\u003e \u003cp\u003eTwo blinded radiologists, one at each site, independently analyzed their respective 100 patients. Measurements were performed on axial source images at a standardized osseous landmark: the level of the maxillary sinus infundibulum. This landmark was selected to provide a simple, reproducible, and clinically applicable reference point. At this level, the maximum internal anteroposterior (AP) diameter, transverse width, and cross-sectional area of the bony NLD were measured bilaterally. The cross-sectional area was subsequently calculated assuming an elliptical shape using the formula:\u003c/p\u003e \u003cp\u003e \u003cb\u003eArea\u0026thinsp;=\u0026thinsp;π \u0026times; (AP diameter/2) \u0026times; (width/2).\u003c/b\u003e \u003c/p\u003e \u003cp\u003eThis efficient calculation was chosen to reflect a practical clinical workflow in which complex manual segmentation is often not feasible. Figure\u0026nbsp;1 illustrates the measurement technique.\u003c/p\u003e \u003cp\u003eFor intra-reader reliability, each radiologist re-measured a randomly selected subset of 50 patients (100 sides) after a 6-week washout period, blinded to their initial results.\u003c/p\u003e \u003cp\u003eReliability and Statistical Analysis\u003c/p\u003e \u003cp\u003eInter-observer reliability was evaluated by comparing the pooled measurements from the two independent readers using intraclass correlation coefficients (ICC, two-way random-effects, absolute agreement, single measure). An ICC\u0026thinsp;\u0026ge;\u0026thinsp;0.80 was prespecified as indicating excellent reliability.\u003c/p\u003e \u003cp\u003eIntra-reader reliability was assessed using repeated measurements and quantified with ICCs and Bland-Altman analysis (to assess reporting bias and 95% limits of agreement). The proportion of repeat measures falling within predefined clinical tolerance limits (\u0026plusmn;\u0026thinsp;1 mm for diameters, \u0026plusmn;\u0026thinsp;2 mm\u0026sup2; for area) was calculated.\u003c/p\u003e \u003cp\u003eStatistical analyses were performed using R software, version 4.2.0. Continuous variables are reported as mean\u0026thinsp;\u0026plusmn;\u0026thinsp;standard deviation and as percentiles. Side-to-side differences were analyzed using paired t-tests. Bootstrap resampling (2,000 iterations) was used to derive confidence intervals for extreme percentiles (2.5th and 97.5th) and the asymmetry cutoff (95th percentile). A p-value\u0026thinsp;\u0026lt;\u0026thinsp;0.05 was considered statistically significant.\u003c/p\u003e"},{"header":"Results","content":"\u003cp\u003eStudy Cohort\u003c/p\u003e \u003cp\u003eA total of 200 adult patients (400 sides) were included. The mean age was 41.2\u0026thinsp;\u0026plusmn;\u0026thinsp;13.6 years (range, 18\u0026ndash;72 years); 52% were female. All CT examinations were technically adequate, and bilateral NLD measurements were successfully obtained in every case.\u003c/p\u003e \u003cp\u003eNormative Values\u003c/p\u003e \u003cp\u003eNLD dimensions demonstrated narrow bilateral distributions, with comparable right- and left-sided values (Fig.\u0026nbsp;2). All cross-sectional area values are derived from direct diameter measurements. Percentile ranges confirmed reproducible reference values across the cohort. A site-stratified analysis showed no significant differences, supporting pooled reporting.\u003c/p\u003e \u003cp\u003ePhysiological Inter-Ocular Asymmetry\u003c/p\u003e \u003cp\u003eAbsolute side-to-side differences in NLD dimensions were small, indicating minimal physiologic asymmetry across the cohort. The median inter-ocular difference was 1.0 mm for AP diameter, 0.0 mm for transverse width, and 3.9 mm\u0026sup2; for cross-sectional area. A median of 0.0 mm indicates that the most common finding was perfect symmetry, although the 95th-percentile cutoff indicates that a range of normal variation exists (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). These thresholds were 4.0 mm for the AP diameter, 2.0 mm for the transverse width, and 23.7 mm\u0026sup2; for the cross-sectional area. Asymmetry exceeding these cutoffs is therefore uncommon in a healthy population and may warrant further clinical consideration.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003ePhysiological Inter-Ocular Asymmetry (n\u0026thinsp;=\u0026thinsp;200 patients)\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"5\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMetric\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eMean\u0026thinsp;\u0026plusmn;\u0026thinsp;SD\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eMedian (IQR)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003e95th percentile cutoff\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003ePrevalence\u0026thinsp;\u0026gt;\u0026thinsp;2 mm\u003c/p\u003e \u003cp\u003e(%, 95% CI)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eΔ AP diameter (mm)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e0.96\u0026thinsp;\u0026plusmn;\u0026thinsp;1.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e1.0 (0\u0026ndash;2)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e4.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e5% (95% CI\u0026thinsp;~\u0026thinsp;2\u0026ndash;8)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eΔ Width (mm)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e0.42\u0026thinsp;\u0026plusmn;\u0026thinsp;0.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.0 (0\u0026ndash;1)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e2.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e3% (95% CI\u0026thinsp;~\u0026thinsp;1\u0026ndash;6)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eΔ Area (mm\u0026sup2;)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e6.2\u0026thinsp;\u0026plusmn;\u0026thinsp;7.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e3.9 (0\u0026ndash;9)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e23.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e4% (95% CI\u0026thinsp;~\u0026thinsp;2\u0026ndash;7)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003ctfoot\u003e \u003ctr\u003e\u003ctd colspan=\"5\"\u003e\u003cb\u003eΔ\u0026thinsp;=\u0026thinsp;absolute side-to-side difference.\u003c/b\u003e\u003c/td\u003e\u003c/tr\u003e \u003c/tfoot\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eReliability\u003c/p\u003e \u003cp\u003eRepeat measurements demonstrated excellent reproducibility (Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). Inter-observer ICCs exceeded 0.88 across all metrics, and intra-reader Bland\u0026ndash;Altman analysis showed negligible bias with limits of agreement within predefined tolerance thresholds. More than 85% of repeat measures fell within tolerance limits, confirming the robustness, site comparability, and reader reproducibility necessary for clinical application across different institutions.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eIntra-Reader Reliability (Repeat Subset, n\u0026thinsp;=\u0026thinsp;50 per reader)\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"4\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMetric\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eInter-Observer ICC (95% CI)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eIntra-Reader ICC (95% CI)*\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eBland-Altman 95% Limits of Agreement\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eAP Diameter (mm)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.91 (0.88\u0026ndash;0.94)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.91 (0.85\u0026ndash;0.95)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u0026minus;1.9 to +\u0026thinsp;2.1 mm\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eTransverse Width (mm)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.89 (0.86\u0026ndash;0.92)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.89 (0.82\u0026ndash;0.93)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u0026minus;1.6 to +\u0026thinsp;1.4 mm\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eCross-Sectional Area (mm\u0026sup2;)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.93 (0.90\u0026ndash;0.95)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.93 (0.87\u0026ndash;0.96)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u0026minus;13.4 to +\u0026thinsp;11.3 mm\u0026sup2;\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003ctfoot\u003e \u003ctr\u003e\u003ctd colspan=\"4\"\u003e\u003cb\u003e*ICC\u0026thinsp;=\u0026thinsp;intraclass correlation coefficient. *Pooled intra-reader estimates from Readers 1 \u0026amp; 2.\u003c/b\u003e\u003c/td\u003e\u003c/tr\u003e \u003c/tfoot\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003eThis study provides reproducible CT-derived normative reference values for the adult bony nasolacrimal duct, together with percentile-based thresholds for physiologic inter-ocular asymmetry. Our principal findings are that NLD dimensions exhibit consistent bilateral distributions and that minor asymmetry is common, whereas significant asymmetry is rare. By defining percentile cutoffs, we establish objective standards for radiologists to distinguish normal anatomic variation from pathologic narrowing. Furthermore, deriving these values from a multi-ethnic urban cohort enhances their generalizability across diverse populations.\u003c/p\u003e \u003cp\u003eOur results expand on previous smaller studies [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e, \u003cspan additionalcitationids=\"CR10 CR11\" citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e] \u0026mdash; which were often limited to single readers without rigorous reliability assessment \u0026mdash; by providing percentile distributions, robust multi-reader reproducibility metrics, and defined asymmetry thresholds across a substantial cohort. The high intraclass correlation coefficients and narrow Bland\u0026ndash;Altman limits confirm that standardized axial measurements at the maxillary infundibulum are reliable across both sites and independent readers. Furthermore, unlike prior studies that relied on multiplanar reformations or measurements along the duct\u0026rsquo;s full course [\u003cspan additionalcitationids=\"CR11\" citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e], we intentionally prioritized clinical utility by standardizing a simple measurement at a single, reproducible axial landmark. This approach, using direct PACS tools on standard source images, seamlessly integrates into the radiologist\u0026rsquo;s existing workflow, thereby enhancing both the practical adoption and the methodological rigor of these normative values. Consequently, while previous research [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e, \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e, \u003cspan additionalcitationids=\"CR12 CR13\" citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e] has primarily focused on describing anatomic differences in patients with established PANDO, our work provides the foundational normative data required to objectively define a narrow bony canal as a potential contributing cause.\u003c/p\u003e \u003cp\u003eThe clinical implications are twofold. First, an AP diameter below the 2.5th percentile (\u0026asymp;\u0026thinsp;5.0 mm) provides an objective definition for a congenitally narrow canal, which is a suspected risk factor for primary acquired nasolacrimal duct obstruction (PANDO) [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. Second, the demonstration of frequent but bounded asymmetry underscores the need for bilateral evaluation, particularly in patients undergoing surgery or presenting with unilateral symptoms. The defined 95th-percentile cutoffs (e.g., \u0026gt;\u0026thinsp;4 mm for AP diameter) provide a quantitative framework for flagging a duct as disproportionately narrow relative to the contralateral side, which could be the underlying substrate for unilateral epiphora.\u003c/p\u003e \u003cp\u003eSeveral considerations temper these findings. The retrospective design limited the ability to correlate with clinical outcomes, and only bony anatomy was assessed; mucosal and soft-tissue components, which also influence obstruction, were beyond the scope of this study. Our methodology, which uses direct linear measurements and a straightforward elliptical-area calculation, was designed to integrate seamlessly into routine radiological practice without specialized software; nevertheless, residual interindividual variability underscores the role for future automated segmentation and deep learning approaches to improve efficiency and scalability [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]. Future studies should link these morphometric data to clinical outcomes, such as surgical success in dacryocystorhinostomy, to assess their prognostic value.\u003c/p\u003e"},{"header":"Conclusion","content":"\u003cp\u003eThis study presents the first multi-dimensional, percentile-based CT normative reference for the adult bony nasolacrimal duct, derived from a large non-surgical cohort, and establishes evidence-based 95th-percentile thresholds for physiologic inter-ocular asymmetry. Validated across two sites and two independent readers, these benchmarks provide immediately applicable standards for distinguishing normal anatomy from pathologic narrowing, characterizing unilateral asymmetry, and guiding pre-procedural planning in sinonasal and lacrimal surgery.\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003e\u003cstrong\u003eAuthor Contribution\u003c/strong\u003e\u003c/h2\u003e\n\u003cp\u003e\u003cstrong\u003eMohamed Ragab Nouh\u003c/strong\u003e \u0026mdash; Guarantor of the integrity of the entire study; contributed to study conception and design; performed literature research; participated in clinical studies; conducted data analysis; contributed to manuscript preparation; performed manuscript editing.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eSaleh Kamal Alzahrani\u003c/strong\u003e \u0026mdash; Contributed to study conception and design; performed literature research; contributed to manuscript preparation; performed manuscript editing.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eIslam Salah Mourad\u003c/strong\u003e \u0026mdash; Participated in clinical studies; performed literature research; contributed to manuscript preparation.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eMostafa Magdy Donia\u003c/strong\u003e \u0026mdash; Performed literature research; participated in clinical studies; contributed to manuscript preparation.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConflict of Interest. \u003c/strong\u003eThe authors declare no conflicts of interest.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding Declaration. \u003c/strong\u003eThe authors received no financial support for this research.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eHuman Ethics and Consent to Participate.\u003c/strong\u003e Institutional review board approval was obtained, and informed consent was waived due to the retrospective design and use of anonymized data.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eAli MJ, Paulsen F (2019) Etiopathogenesis of Primary Acquired Nasolacrimal Duct Obstruction: What We Know and What We Need to Know. Ophthalmic Plast Reconstr Surg 35:426\u0026ndash;433. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1097/IOP.0000000000001310\u003c/span\u003e\u003cspan address=\"10.1097/IOP.0000000000001310\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAli MJ (2023) Etiopathogenesis of primary acquired nasolacrimal duct obstruction (PANDO). 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J Clin Med 14:778. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.3390/jcm14030778\u003c/span\u003e\u003cspan address=\"10.3390/jcm14030778\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"surgical-and-radiologic-anatomy","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"sara","sideBox":"Learn more about [Surgical and Radiologic Anatomy](http://link.springer.com/journal/276)","snPcode":"276","submissionUrl":"https://submission.nature.com/new-submission/276/3","title":"Surgical and Radiologic Anatomy","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Nasolacrimal duct, CT imaging, Normative values, Interocular asymmetry, Reliability, Preoperative planning","lastPublishedDoi":"10.21203/rs.3.rs-9118039/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-9118039/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003ch2\u003ePurpose\u003c/h2\u003e \u003cp\u003eTo establish the first multi-dimensional, percentile-based CT normative reference values for the bony nasolacrimal duct (NLD) in a large non-surgical adult cohort, and to define 95th-percentile thresholds for physiologic inter-ocular asymmetry.\u003c/p\u003e\u003ch2\u003eMaterials and Methods\u003c/h2\u003e \u003cp\u003eIn this retrospective study of 200 adults (mean age, 41.2\u0026thinsp;\u0026plusmn;\u0026thinsp;13.6 years; 52% female), two blinded radiologists at two independent sites measured anteroposterior (AP) diameter, transverse width, and cross-sectional area bilaterally at a standardized axial landmark (maxillary sinus infundibulum). Cross-sectional area was calculated from the linear diameters, assuming an elliptical cross-section. Reliability was assessed using intraclass correlation coefficients (ICC) and Bland\u0026ndash;Altman analysis. Normative percentiles and 95th-percentile asymmetry thresholds were derived.\u003c/p\u003e\u003ch2\u003eResults\u003c/h2\u003e \u003cp\u003eMean bilateral values were comparable: AP diameter 8.0\u0026ndash;8.1\u0026thinsp;\u0026plusmn;\u0026thinsp;2.0\u0026ndash;2.1 mm, transverse width 5.1\u0026ndash;5.2\u0026thinsp;\u0026plusmn;\u0026thinsp;0.8\u0026ndash;0.9 mm, and cross-sectional area 32.8\u0026ndash;33.1\u0026thinsp;\u0026plusmn;\u0026thinsp;9.4\u0026ndash;9.7 mm\u0026sup2;. The 2.5\u0026ndash;97.5th percentile ranges were 5.0\u0026ndash;13.0 mm for AP diameter, 4.0\u0026ndash;7.0 mm for transverse width, and 15.7\u0026ndash;61.3 mm\u0026sup2; for cross-sectional area. Physiologic asymmetry was small: median Δ diameter, width, and area were 1.0 mm, 0 mm, and 3.9 mm\u0026sup2;, respectively. The 95th percentile cutoffs for asymmetry were 4.0 mm, 2.0 mm, and 23.7 mm\u0026sup2;, respectively. Intra-reader ICCs ranged from 0.88\u0026ndash;0.93, with Bland-Altman bias\u0026thinsp;\u0026lt;\u0026thinsp;0.2 mm for diameters and \u0026lt;\u0026thinsp;1.0 mm\u0026sup2; for area.\u003c/p\u003e\u003ch2\u003eConclusion\u003c/h2\u003e \u003cp\u003eThis study presents the first multi-dimensional, percentile-based CT normative reference for the adult bony nasolacrimal duct from a large non-surgical cohort, including validated 95th-percentile asymmetry thresholds for clinical reporting and pre-procedural surgical planning.\u003c/p\u003e","manuscriptTitle":"Computed Tomography-Derived Normative Values and Physiologic Asymmetry of the Bony Nasolacrimal Duct in Adults","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-05-04 06:01:20","doi":"10.21203/rs.3.rs-9118039/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"editorInvitedReview","content":"","date":"2026-05-05T09:07:55+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"43686068225334342143325553199363315318","date":"2026-04-26T15:06:43+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"186786351030689181229833971517149698041","date":"2026-04-26T08:18:53+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2026-04-21T08:50:17+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2026-03-19T12:57:01+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2026-03-17T09:13:35+00:00","index":"","fulltext":""},{"type":"submitted","content":"Surgical and Radiologic Anatomy","date":"2026-03-13T20:44:43+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"surgical-and-radiologic-anatomy","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"sara","sideBox":"Learn more about [Surgical and Radiologic Anatomy](http://link.springer.com/journal/276)","snPcode":"276","submissionUrl":"https://submission.nature.com/new-submission/276/3","title":"Surgical and Radiologic Anatomy","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"24a5b94b-3820-44bb-8b84-e324b6cfc970","owner":[],"postedDate":"May 4th, 2026","published":true,"recentEditorialEvents":[{"type":"editorInvitedReview","content":"","date":"2026-05-05T09:07:55+00:00","index":16,"fulltext":""}],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2026-05-04T06:01:20+00:00","versionOfRecord":[],"versionCreatedAt":"2026-05-04 06:01:20","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-9118039","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-9118039","identity":"rs-9118039","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}