Anatomic features of congenital nasolacrimal duct obstruction: a comparative computed tomography study

Introduction

Congenital nasolacrimal duct obstruction (CNLDO) is a common condition in newborns, with an incidence of up to 20%, and is marked by continuous tearing and mucopurulent discharge (1,2). Currently, it is believed that the CNLDO is primarily caused by the valve of Hasner, located at the opening of the nasolacrimal duct (NLD) in the nasal cavity. Clinical observations show that CNLDO sometimes resolves spontaneously, typically before the age of 18 months (3,4). However, in cases where spontaneous resolution does not occur, surgical intervention is usually required, including lacrimal probing, intubation, balloon catheter dilatation, or dacryocystorhinostomy (DCR) (5-9). In adult patients with acquired NLD obstruction, significant anatomical changes in the lacrimal sac fossa (LF) and NLD are commonly observed and may affect surgical planning (10,11). This raises the need to investigate whether similar structural changes occur in pediatric CNLDO patients.

Cranial computed tomography (CT) is routinely used as a preoperative examination for most patients with CNLDO. Since it can accurately illustrate the bony structures of the orbit and nasal region, cranial CT is well-suited for investigating local structural changes in CNLDO (12,13). However, most existing studies have focused on healthy children, and their findings largely reflect the normal developmental processes of the lacrimal system in pediatric populations (14,15). In order to reveal the anatomical changes under pathological conditions of CNLDO, it is essential to include CT findings from the patients.

A few studies have investigated various malformations of the lacrimal drainage system in children with CNLDO. Researchers have categorized the malformations into fundamental and special types, which represent narrowing of the distal and upper segments of the NLD, respectively (16). Some have specifically focused on the anatomical variations of additional structures, which can complicate intubation procedures, yet are not directly associated with symptoms such as epiphora (17). Quantitative analyses have also been conducted to clarify the CT characteristics of CNLDO, including measurements of bony angles in dacryocystography images and NLD diameter (18,19). One important viewpoint suggests that enlargement of the NLD on the obstructed side in CNLDO is primarily attributable to increased hydrostatic pressure within the fluid column of the duct (15,19).

However, these studies have several limitations. Despite the critical importance of evaluating the LF in CNLDO patients, research in this area remains limited, with most measurement-based studies focusing solely on the NLD. Moreover, many studies have lacked healthy children as controls, making it difficult to draw robust conclusions about structural changes associated with CNLDO.

Therefore, this study aimed to comprehensively investigate the anatomical features of the LF and NLD, as well as the presence of sinusitis in children with CNLDO. By classifying the patients into two groups, those with dacryocystitis and those without (20,21), and comparing them with paired healthy controls, we aimed to reveal the radiological changes in CNLDO relative to the normal NLD (Figure 1). This approach provides deeper insights into the pathophysiology of CNLDO and enhances the understanding of its surgical management. We present this article in accordance with the STROBE reporting checklist (available at https://qims.amegroups.com/article/view/10.21037/qims-2025-827/rc).

Figure 1 The flow diagram of the study: CNLDO patients with or without dacryocystitis were compared to their matched controls respectively. CNLDO, congenital nasolacrimal duct obstruction; CT, computed tomography.

Methods

Design and patients

In this retrospective comparative study, we reviewed the medical records of CNLDO patients and the healthy control children treated at the Eye & ENT Hospital of Fudan University from January 2022 to December 2024. The study was approved by the Ethics Committee of the Eye & ENT Hospital of Fudan University (No. 2023164) and conducted in accordance with the Declaration of Helsinki and its subsequent amendments. The requirement for individual consent for this retrospective analysis was waived.

We included unilateral CNLDO patients under 18 years old who underwent cranial CT scans before surgery. CT was performed based on clinical judgment, mainly for patients with persistent symptoms requiring detailed assessment (e.g., lacrimal fossa and adjacent bony pathology), to guide preoperative planning. The diagnosis was based on epiphora symptoms and lacrimal irrigation tests. If purulent reflux occurred during lacrimal irrigation, chronic dacryocystitis was further diagnosed. Both unilateral lacrimal obstruction and chronic dacryocystitis were further confirmed during surgery through intraoperative lacrimal probing and irrigation. Based on whether purulent reflux was observed, the included CNLDO cases were divided into two groups: the dacryocystitis group and the non-dacryocystitis group. For the control group, we included pediatric patients under 18 years old who required cranial CT for preoperative assessment of congenital sensorineural hearing loss prior to cochlear implantation. Preoperative medical records were reviewed, and any cases with suspected craniofacial anomalies or syndromic disorders were excluded. The control group was matched with the study group by age and gender in a 1:1 ratio, with an acceptable age difference of ±6 months.

The enrolled CNLDO patients were excluded if they had bilateral obstruction, a history of lacrimal surgery, facial fractures, or significant trauma. For the control group, in addition to these criteria, participants were excluded if they reported symptoms of epiphora.

Analyses were conducted separately. For the dacryocystitis group, the obstructed sides, non-obstructed sides, and the corresponding matched controls (with bilateral sides values averaged) were compared. For the non-dacryocystitis group, the same three groups were compared: obstructed side, non-obstructed side, and the matched controls. Additionally, the prevalence of sinusitis was examined across the different groups.

CT acquisition

All CT images were acquired in helical mode using a multidetector-row scanner (Siemens Medical Systems, Erlangen, Germany) with a slice thickness of 0.75 mm, covering the orbits and nasal structures at a tube voltage of 120 kV and a current of 230 mA. The images were analyzed on a digital image workstation (Carestream CGRIS; Carestream Health, Rochester, NY, USA). All measurements were performed by one author (W.W.), who was blinded to demographic and clinical information during the analysis. A second observer (Y.T.) independently repeated measurements in a subset of cases, and intraclass correlation coefficients (ICCs) for interobserver reliability ranged from 0.757 to 0.870 across parameters, indicating good consistency. The analysis was based on a window setting of C 700 W 4,000.

Image analysis

The measured parameters included LF height, LF width, frontal process thickness, NLD height, the narrowest NLD width, and upper NLD width. To help evaluate the parameters, six axial levels were defined on the CT images. The upper LF border corresponded to the uppermost axial level of the LF (Figure 2A). The level immediately superior to the lower LF border was used to measure LF width and frontal process thickness (Figure 2B). The lower LF border represented the last axial level before the appearance of the complete ring of the NLD (Figure 2C). The upper NLD border indicated the first axial level showing the complete ring of the NLD (Figure 2D). The narrowest NLD width was measured at the axial level where the duct exhibited its smallest diameter (Figure 2E). The lower NLD border corresponded to the section where the NLD opens into the nasal cavity (Figure 2F) (22).

Figure 2 Methods of measurement on the CT scans. (A-C) The upper LF border, the level prior to the lower LF border and the lower LF border. The distance between the upper LF border and the lower LF border determined the LF height. The LF width (line 1) and frontal process thickness (line 2) were measured on the level prior to the lower LF border. (D-F) The upper NLD border, the level of the narrowest NLD width, and the lower NLD border. The distance between the upper NLD border and the lower NLD border determined the NLD height. The upper NLD width was measured on the upper NLD border. CT, computed tomography; LF, lacrimal sac fossa; NLD, nasolacrimal duct.

The LF height refers to the distance between the upper LF border and the lower LF border (Figure 2A,2C). This measurement was calculated by multiplying the number of sections by 0.75 mm, as reported in previous studies (22,23). In addition, the LF width was measured as the distance between the anterior extent of the LF and the posterior lacrimal crest (Figure 2B, line 1), whereas the frontal process thickness was determined at the midpoint between the anterior extent of the LF and the lacrimomaxillary suture in the level prior to the lower LF border (Figure 2B, line 2) (20). Furthermore, the NLD height was defined as the distance between the upper NLD border and the lower NLD border (Figure 2D,2F), also calculated by multiplying the number of sections by 0.75 mm. Finally, the narrowest NLD width and the upper NLD width were both determined as the transverse distances of the NLD. Specifically, the narrowest NLD width was obtained at the section with the smallest diameter of the NLD (Figure 2E), whereas the upper NLD width was measured at the upper NLD border (Figure 2D) (24).

In this study, sinusitis was evaluated in the frontal, maxillary, and ethmoid sinuses. It was defined by the presence of mucosal thickening, partial opacification, or complete opacification of the sinus, in reference to the criteria described in the Lund-Mackay scoring system (Figure S1) (10). Since sinusitis often involves multiple sinuses and may not be reliably lateralized, we assessed it at the patient level without differentiating between sides to minimize misclassification.

Statistical analysis

Statistical analyses were performed using the software SPSS 29.0 (IBM Corp., Armonk, NY, USA) and R statistical software (version 4.3.3; R Foundation for Statistical Computing, Vienna, Austria). To compare CNLDO patients with controls, we utilized violin plots that display the 25th percentile, median, 75th percentile, and mean values. Mann-Whitney U tests were conducted, due to non-normal distribution of several variables, to compare the control group with both the obstructed and unobstructed sides of CNLDO patients, respectively. Chi-squared test was used to compare the prevalence of sinusitis among different groups. A significance level of P<0.05 was considered statistically significant. For variables showing statistically significant differences, Cohen’s d was calculated to assess the effect size.

Results

A total of 39 CNLDO patients were enrolled in the study after excluding 2 bilateral CNLDO cases and 2 patients with a history of intubation surgery from the initial 43 cases. Based on the diagnosis of chronic dacryocystitis, these 39 cases were categorized into two groups: 18 with dacryocystitis and 21 without (Figure 1). The median age in the two groups was 2.92 and 2.58 years, respectively. Age ranged from 0.33 to 11.08 years in the former, and from 0.83 to 13.92 years in the latter. Both groups had similar age distributions, with the majority of cases concentrated between 2 and 5 years. The detailed age distribution is shown in Figure S2. Gender was also distributed fairly evenly in both groups: there were 9 males and 9 females in the group with dacryocystitis, whereas the non-dacryocystitis group included 10 males and 11 females. As for the affected eye, the dacryocystitis group had 8 cases of right eye obstruction and 10 of left eye obstruction, whereas the other group had 12 and 9 cases, respectively. The details of the surgical procedures that were conducted are presented in Table 1.

In the dacryocystitis group (Figure 3), the narrowest NLD width and upper NLD width were significantly larger on the obstructed sides compared with the paired control sides (3.90±0.70 vs. 2.82±0.47 mm, 4.72±1.10 vs. 3.43±0.79 mm, both P<0.001), with large effect sizes [Cohen’s d=1.81, 95% confidence interval (CI): 1.00–2.62 and 1.35, 95% CI: 0.59–2.10, respectively], whereas no significant difference was observed on the unobstructed sides compared to the controls (2.85±0.68 mm, 3.48±0.68 mm, P=0.832 and 0.749, respectively). For other parameters, the obstructed sides also showed a significant increase in LF width compared to the controls (5.57±1.40 vs. 4.48±0.89 mm, P=0.034, Cohen’s d=0.93, 95% CI: 0.21–1.64), but no significant differences in LF height (11.93±1.79 vs. 11.33±2.25 mm, P=0.260), frontal process thickness (1.53±0.35 vs. 1.78±0.44 mm, P=0.067), or NLD height (5.13±1.89 vs. 4.82±1.54 mm, P=0.783). Similarly, the unobstructed sides showed no significant differences in LF height (12.06±1.80 mm, P=0.158), LF width (4.69±0.88 mm, P=0.622), frontal process thickness (1.77±0.45 mm, P=0.702), or NLD height (5.21±1.72 mm, P=0.554) compared to the controls. Bonferroni-adjusted P values are provided in Table S1.

Figure 3 Comparisons of the anatomic structures between the dacryocystitis group and the control group. Violin plots showed quartiles and mean (yellow diamond). *, P<0.05; ***, P<0.001; ns, not significant. LF, lacrimal sac fossa; NLD, nasolacrimal duct.

In the non-dacryocystitis group (Figure 4), the narrowest NLD width was significantly larger on the obstructed sides compared to the paired control sides (3.38±0.70 vs. 2.82±0.47 mm, P=0.009, Cohen’s d=0.94, 95% CI: 0.28–1.60), whereas no significant difference was observed on the unobstructed sides compared to the controls (2.96±0.74 mm, P=0.887). For other parameters, the obstructed sides showed no significant differences from the paired control sides: LF height (11.60±1.92 vs. 11.44±2.67 mm, P=0.741), LF width (4.97±0.94 vs. 4.43±0.76 mm, P=0.118), frontal process thickness (1.66±0.45 vs. 1.79±0.41 mm, P=0.379), NLD height (4.99±2.06 vs. 4.88±1.47 mm, P=0.935), and upper NLD width (3.95±0.81 vs. 3.43±0.78 mm, P=0.056). Similarly, the unobstructed sides showed no significant differences in any parameter compared to the paired control sides, including LF height (11.63±1.87 mm, P=0.769), LF width (4.46±0.93 mm, P=0.998), frontal process thickness (1.71±0.45 mm, P=0.533), NLD height (5.06±1.98 mm, P=0.866), and upper NLD width (3.56±0.85 mm, P=0.751). Bonferroni-adjusted P values are provided in Table S1.

Figure 4 Comparisons of the anatomic structures between the non-dacryocystitis group and the control group. Violin plots showed quartiles and mean (yellow diamond). **, P<0.01; ns, not significant. LF, lacrimal sac fossa; NLD, nasolacrimal duct.

Additionally, the prevalence of sinusitis was evaluated in the different groups (Table 2). Among the dacryocystitis group, 5 patients (27.8%) had signs of sinusitis, compared to 4 patients (22.2%) in the matched healthy control group (P=0.70). In the non-dacryocystitis group, 5 patients (23.8%) exhibited sinusitis, which was identical to the 5 patients (23.8%) among their respective controls (P=1.00).

Discussion

Few CT-based studies on CNLDO have included healthy individuals as a control group. In our study, we were able to enroll both patients and healthy cases, enabling a controlled comparison of CT findings in CNLDO. Notably, we subdivided patients based on the presence or absence of dacryocystitis and found that many of the observed changes were more pronounced in cases complicated by dacryocystitis.

A notable phenomenon is the increase in NLD width observed on the obstructed sides in both the dacryocystitis and non-dacryocystitis groups compared to the controls. This pattern broadly aligns with prior reports of NLD enlargement on the obstructed side in CNLDO (15,19). In this study, we used the narrowest transverse width of the NLD as the primary parameter to reflect the enlargement of the NLD. This approach has been widely applied in many CT studies of adult patients with NLD obstruction and is a reliable method, particularly given the highly individualized morphology of the NLD (24). The anterior–posterior inclination of the NLD in the coronal plane causes its axial section to take on an oval shape. Therefore, measuring the transverse width provides a more precise assessment. Additionally, the upper NLD width, measured at the initial segment of the NLD, was included in the analysis. However, an enlargement of the upper NLD width was observed only in the dacryocystitis groups.

An enlarged LF width was observed exclusively on the obstructed sides in the dacryocystitis group compared to the controls, representing a novel finding. Nevertheless, this alteration was not found in the non-dacryocystitis groups. LF width is an important anatomical parameter in DCR, as it reflects the horizontal surgical exposure range. The observed LF widening on the obstructed sides may potentially facilitate surgical access, although intraoperative confirmation was beyond the scope of this study. Furthermore, this may explain why the upper NLD width, at the junction between the NLD and LF, was similarly enlarged only in the dacryocystitis group. The expansion of the bony LF also impacts the upper segment of the NLD. Furthermore, the thickness of the frontal process, another important structure related to DCR, remains unchanged in CNLDO patients. Similarly, neither LF height nor NLD height differed from controls in CNLDO patients.

Briefly, the pathological changes in the dacryocystitis group were more extensive and severe compared to those in the non-dacryocystitis group. Thus, we propose an exploratory hypothesis that the chronic infection is one of the key factors contributing to the anatomical alterations in CNLDO. Traditionally, researchers have attributed the enlarged NLD width in CNLDO to increased hydrostatic pressure within the fluid column of the NLD (15,19). We support this view, as we also observed the same results in our non-dacryocystitis groups compared to controls. However, infectious factors should not be ignored. Concurrent chronic dacryocystitis can lead to bone resorption and remodeling, ultimately resulting in enlargement, as reported in several studies (10,25), though adult-derived mechanisms may not fully apply to pediatric CNLDO owing to differences in skeletal maturity. Taken together, the anatomical changes in CNLDO may result from a combination of elevated NLD hydrostatic pressure and possible effects of chronic inflammation. This perspective may also help to explain the anatomic changes in adult NLD obstruction: although NLD enlargement is uncommon due to full skeletal maturity and reduced susceptibility to pressure-related changes, LF enlargement may possibly be associated with chronic infection (10,24). Our findings are consistent with this perspective, yet longitudinal or histopathological studies will be essential to validate and clarify these mechanisms.

Certainly, all the anatomical changes described above are observed exclusively on the obstructed sides of patients with CNLDO, whereas the unobstructed sides appear to show no difference from those of healthy controls. This asymmetrical pathological phenomenon indicates that the anatomical alterations are secondary to the obstruction of CNLDO, rather than being its primary causes. However, since our study has a retrospective design, a causal relationship cannot be definitively established. In addition, this finding also confirms that the unaffected sides in CNLDO patients can serve as a valid control in CT-based studies of CNLDO.

Studies have reported a high prevalence of sinusitis in the adult NLD obstruction cases (26,27). As sinusitis often involves multiple sinuses and may not be reliably localized to one side, our study did not differentiate sinusitis by the affected eye. We found no association between sinusitis and CNLDO, nor did we observe an increased prevalence of sinusitis in the dacryocystitis group. These findings suggest that chronic inflammation in CNLDO remains localized to the lacrimal sac and NLD, but may also partially be attributable to our small sample size.

This study has several limitations. First, CT data were not obtained from healthy children due to ethical concerns, and the control patients did not undergo lacrimal irrigation testing. However, ear diseases are minimally related to CNLDO, and performing irrigation tests in children without epiphora was challenging due to poor compliance and ethical considerations. Second, CT without dacryocystography cannot clearly define the upper boundary of the LF or evaluate intraluminal obstruction and mucosal conditions. Although dacryocystography provides more functional detail, it requires additional contrast injection and increases radiation exposure. Future studies could further consider non-radiation imaging modalities such as MRI or ultrasound to conduct imaging studies for CNLDO. Third, although the control group consisted of pediatric patients with congenital sensorineural hearing loss screened to exclude craniofacial anomalies or syndromic disorders, residual confounding cannot be fully ruled out. Fourth, the relatively small sample size, due to the limited number of CNLDO patients requiring both surgical intervention and cranial CT, prevented reliable multiple-comparison correction. This increases the risk of type I errors and reduces the statistical validity of our results. Therefore, the generalizability of our findings is limited, and statistically significant results should be interpreted with caution.

Conclusions

CNLDO is often accompanied by expansion of the LF and the NLD, both occurring on the obstructed side without affecting the non-obstructed side. In CNLDO without chronic dacryocystitis, a significant increase in NLD width can be observed. In CNLDO with chronic dacryocystitis, enlargement occurs in both the NLD and the LF, and is more pronounced than in cases without dacryocystitis. There appears to be no significant correlation between sinusitis and CNLDO. We hypothesize that these structural expansions are driven by infectious factors, with elevated hydrostatic pressure in the obstructed NLD also playing a contributing role.

Acknowledgments

None.

Footnote

Reporting Checklist: The authors have completed the STROBE reporting checklist. Available at https://qims.amegroups.com/article/view/10.21037/qims-2025-827/rc

Data Sharing Statement: Available at https://qims.amegroups.com/article/view/10.21037/qims-2025-827/dss

Funding: This study was supported by the National Natural Science Foundation of China (grant No. 82371024 to L.G.), and the Shanghai Committee of Science and Technology Program (grant Nos. 22Y11910300 & 24CL2900700 to L.G.).

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://qims.amegroups.com/article/view/10.21037/qims-2025-827/coif). The authors have no conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. The study was approved by the Ethics Committee of the Eye & ENT Hospital of Fudan University (No. 2023164) and conducted in accordance with the Declaration of Helsinki and its subsequent amendments. Individual consent for this retrospective analysis was waived.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

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