Diversity in Lacrimal Pathway Morphology Among Japanese Patients with Congenital Nasolacrimal Duct Obstruction

doi:10.21203/rs.3.rs-3590040/v1

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Diversity in Lacrimal Pathway Morphology Among Japanese Patients with Congenital Nasolacrimal Duct Obstruction

https://doi.org/10.21203/rs.3.rs-3590040/v1

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Objective:

This study aimed to explore the diversity in lacrimal pathway morphology among Japanese patients with congenital nasolacrimal duct obstruction (CNLDO) by examining dacryocystography (DCG) images.

Study Design:

Prospective observational study

Methods:

The study involved 64 patients who underwent DCG prior to undergoing general anesthesia surgery for unilateral CNLDO at our institution between July 2012 and February 2023. Several parameters were measured from the sagittal section DCG images: (1) The angle between the lacrimal sac and the nasolacrimal duct, (2) The angle between the superior orbital rim, the center of the lacrimal sac, and the nasolacrimal duct, (3) The length of the bony nasolacrimal duct, (4) The length of the lacrimal sac. Additionally, following parameters were measured from coronal section images: (5) The angle formed by the lacrimal sac and the nasolacrimal duct, (6) The angle formed by the lacrimal sac concerning the midline.

Results:

The average age of the patients was 34.3 months, ranging from 14 to 84 months. The mean ± standard deviation of the measurements of the above parameters were (1) –1.2 ± 16.5° (range, –44.6° to +46.6°), (2) –5.0 ± 10.3° (range, –24.0° to +19.0°), (3) 8.0 ± 2.5 mm (range, 3.1 mm to 14.8 mm), (4) 10.2 ± 2.4 mm (range, 6.5 mm to 16.0 mm), (5) 15.6 ± 11.2° (range, –16.8° to +41.0°), (5) 15.1 ± 5.2° (range, +3.3° to +29.8°). Our study revealed that all parameters, except for parameter (4) (length of the lacrimal sac), conformed to a normal distribution, as determined by the Shapiro-Wilk test.

Conclusions:

This study offers valuable anthropometric data derived from DCG images, and the results emphasize the substantial variability in lacrimal pathway morphology among individuals. Moreover, probing with straight probes was considered anatomically infeasible in 25.0% of cases in the patients included in this study.

These findings have the potential to impact the diagnosis and treatment planning for CNLDO.

Ophthalmology

congenital nasolacrimal duct obstruction

dacryocystography

Congenital nasolacrimal duct obstruction (CNLDO) is primarily attributed to the congenital obstruction of the distal portion of the nasolacrimal duct (NLD), often characterized by a membranous obstruction.(1) CNLDO has a notable spontaneous resolution rate, ranging from 89–96%, with conservative management typically resulting in resolution within the first 12 months.(2–4) Patients who do not achieve spontaneous resolution necessitate surgical intervention. Globally, the primary surgical approach is probing. Probing involves the insertion of a metal bougie into the lacrimal pathway from the punctum to the distal end of the NLD, where an obstruction is typically located, to create a perforation. Therefore, understanding the morphology of the lacrimal pathway is of crucial importance for the success of probing. Prior investigations have discovered significant variations in the morphology of the lacrimal pathway in adulthood. However, there have been few studies investigating the detailed analysis of the lacrimal pathway in pediatric CNLDO.

In our present investigation, we aim to conduct a morphological analysis of the lacrimal drainage system in pediatric CNLDO patients using DCG images obtained under general anesthesia at our institution. Our study seeks to establish a foundational understanding of lacrimal passage diversity in children, which holds great potential for enhancing the future diagnosis and treatment of CNLDO.

Patient Selection

We reviewed the medical records for 204 patients who underwent surgery under general anesthesia as part of a prospective observational study on pediatric lacrimal drainage system obstruction. The study spanned from November 2011 to April 2023 at Kanagawa Children's Medical Center in Japan. Specifically, we focused on the analysis of 64 patients with unilateral CNLDO who had undergone DCG before probing. The diagnosis of CNLDO was established based on clinical symptoms of epiphora and mucous discharge, and further confirmed through the fluorescein dye disappearance test. Patients were excluded if they presented with bilateral involvement, incomplete obstruction, punctum or canaliculus obstruction, congenital malformation syndromes, congenital NLD agenesis, facial anomalies, dysmorphisms, congenital dacryocystocele, a history of epidemic keratoconjunctivitis infection, facial trauma, or eyelid injury from this study (Fig. 1).

DCG procedure

Patients with a documented history of allergy to contrast media or iodine were not included in the examination. Prior to the surgical procedure, DCG was performed under general anesthesia. The lacrimal pathway was rinsed with saline before the examination. Images in both coronal and sagittal sections were captured following the injection of a nonionic, water-soluble contrast medium (Iopamidol, 300mg/mL) through the dilated upper and lower lacrimal punctum, using a mobile X-ray system with a minimal radiation dose (mean dosage, XX µSv). Dedicated computer software (RapideyeCore v1.5; Canon Medical System Corp., Tochigi, Japan ) was employed to measure the length and angles from these images.

Investigated Parameters on DCG Images

In our analysis of DCG images, we examined six specific parameters. Four of these measurements were acquired from sagittal section images. The first parameter was the angle between the LS and the NLD (sagittal LS–NLD angle). The second parameter was the angle formed by the SOR, the center of the LS, and the NLD (SOR–LS–NLD angle) (Fig. 2). The described technique was employed to assess the SOR–LS–NLD angle. Initially, a straight line was drawn from the center of the LS towards the SOR and the point where this line intersected the SOR was identified as the tangent point. Subsequently, the angle formed between the line connecting the tangent point on the SOR to the center of the LS and the line linking the center of the LS with the distal end of the interosseous NLD was measured. Moreover, we assessed the lengths of the bony NLD (bNLD length) and the LS (LS length) within the sagittal section (Fig. 3). Moreover, we assessed whether the trajectory of the bNLD is impeded by the SOR in our analysis of the sagittal section (Fig. 4). In particular, we extended the bNLD line anteriorly to ascertain if it encountered any obstruction by the SOR. If this path is impeded, it is expected to pose a challenge for the passage of a straight bougie through the nasolacrimal duct due to this interference caused by the SOR.

Regarding the coronal section, we evaluated two more parameters (Fig. 5). The first was the angle between the LS and the NLD (coronal LS–NLD angle), and the second parameter involved measuring the angle formed by the LS in relation to the midline, which extends through the nasal septum (LS–Midline angle). For sagittal section measurements, angles were designated by positive and negative values to represent anterior and posterior inclination, respectively. In contrast, for coronal section measurements, angles were designated by positive and negative values to indicate medial and lateral inclination, respectively.

Statistical Analysis

Statistical analyses were conducted using the online statistics calculator DATAtab (Graz, Austria; URL https://datatab.net). The Shapiro–Wilk test was utilized to assess the normal distribution of measurement data, with a p-value greater than 0.05 indicating normality in the distribution.

Ethical Approval and Consent to Participate

The study adhered to the principles of the Declaration of Helsinki. The research protocol and informed consent/assent forms received approval from Kanagawa Children's Medical Center, Japan. Written informed consent was obtained from the parents or guardians of all participating patients. Additionally, consent for the publication of identifying information and images was obtained from the legal guardians of all patients.

Breakdown

This study included 64 unilateral CNLDO patients, 41 (64.1%) male and 23 (35.9%) female. Among these, 57.8% were on the right side (37 cases), and 42.2% were on the left (27 cases). The mean ± standard deviation of the age of patients at the time of surgery, which also represents the time of data measurement, was 34.3 ± 19.2 months, ranging from 14 to 84 months. Regarding physical measurements, the average height of the participants was 90.1 ± 11.4 cm (range, 75.1 cm to 119.2 cm). The average weight was 13.4 ± 3.2 kg (8.6 kg to 21.2 kg).

Sagittal LS-NLD angle

The “Sagittal LS-NLD angle” is defined as the angle formed by the long axis of the LS and the long axis of the NLD when observed in the sagittal section. We designated an anterior inclination as a positive value. On average, we observed a posterior inclination of − 1.2 ± 16.5°. We found that anterior inclination, characterized by LS-NLD angles greater than 0°, was observed in 24 cases (37.5%). Conversely, posterior inclination, defined by LS-NLD angles less than 0°, was identified in 31 cases (48.4%). The mean angle for the group with anterior inclination was + 10.7 ± 11.2° (ranging from 0° to + 46.6°). In contrast, the group with posterior inclination had a mean angle of − 13.9 ± 10.9° (ranging from − 0.8° to − 44.6°). Our measurements displayed a pattern consistent with a normal distribution, as affirmed by the Shapiro-Wilk test, which yielded a p-value of 0.69 (Fig. 6).

SOR-LS-NLD angle

The "SOR-LS-NLD angle" denotes an angle formed by two lines within the sagittal section: one extending from the SOR to the center of the LS, and the other connecting the center of the LS to the NLD. An anterior inclination was defined as a positive value (Figure). On average, we recorded a posterior inclination of − 5.0°± 10.3°. We observed anterior inclination was observed in 16 cases (25.0%), whereas the posterior inclination in 44 cases (68.8%). For the group with anterior inclination, the mean angle was + 6.8 ± 6.6° (ranging from 0° to + 19.0°). In contrast, the group with posterior inclination had a mean angle of − 10.3 ± 6.5° (ranging from − 0.4° to − 24.0°). Our measurements conformed to a normal distribution (p = 0.25).

bNLD length

The “bNLD length” pertains to the measurement of the bony NLD's length as observed in the sagittal section view of DCG images. The average NLD length was recorded at 8.0 ± 2.5 mm. The spectrum of bNLD lengths ranged from 3.1 mm to 14.8 mm. Our measurements conformed to a normal distribution (p = 0.62).

LS length

The “LS length” represents the measurement of the longitudinal axis of the LS as observed in the sagittal section. The mean LS length was determined to be 10.2 ± 2.4 mm. LS length values ranged from 6.5 mm to 16.0 mm. It is worth noting that our measurements did not adhere to a normal distribution, a finding verified by the Shapiro-Wilk test (p = 0.036).

SOR interference

When the anteriorly extended path of the bNLD is interfered with the SOR in a sagittal section, it is anticipated to be challenging to pass a straight probe through the NLD due to this interference by the SOR. Among the 64 cases in our study, 16 (25%) encountered this specific interference.

Coronal LS-NLD angle

The "Coronal LS-NLD angle" denotes the angle of inclination from the lacrimal sac to the nasolacrimal duct in a coronal section, with medial inclination designated as a positive value. On average, we observed a medial inclination of + 15.6 ± 11.2°. The range for this angle varied from a maximum medial inclination of + 41.0°to a maximum lateral inclination of − 16.8°. Our measurements exhibited conformity to a normal distribution pattern (p = 0.74).

Coronal Medial-LS angle

The "Coronal Medial-LS angle" is defined as the angle created by the long axis of the lacrimal sac and the median line running through the nasal septum in the coronal section. The average angle measured 15.1 ± 5.2°. This angle ranged from a minimum of 3.3° to a maximum of 29.8°. Our measurements demonstrated a normal distribution pattern (p = 0.27).

CNLDO has a notable spontaneous resolution rate with conservative management typically resulting in resolution within the first 12 months.(2–4) However, the optimal timing for surgical intervention in cases where spontaneous resolution is not achieved remains controversial.(5) Early probing, while feasible under local anesthesia, raises concerns about potentially intervening in cases that might resolve spontaneously with time. Late probing, performed after the first year of life, offers the advantage of allowing for potential spontaneous resolution prior to surgical intervention. Nevertheless, it necessitates the use of general anesthesia, which presents its own set of considerations.(2, 4, 6–8) Several observational studies have reported an inverse relationship between patient age and therapeutic success, indicating that older patients tend to exhibit lower rates of therapeutic success when undergoing probing.(9, 10)

Little is known about the radiologic details of the lacrimal drainage system in children.(11–14) To the best of our knowledge, this study represents the first attempt to measure anthropometric parameters of the lacrimal drainage system in patients with CNLDO using DCG images. The length and morphology of the lacrimal drainage system exhibit considerable variations among individuals and ethnic groups.(15–20) Our group previously analyzed the morphology of the normal lacrimal pathway in adults within a Japanese population. This analysis was based on DCG images obtained using cone-beam computed tomography (CBCT).(21) These findings indicated that the average sagittal LS-NLD angle in adults was − 1.2 ± 16.5°. Consequently, the value of + 10.7 ± 11.2° observed in CNLDO patients in this study represented a significant anterior inclination in comparison to the measurements in adults. Although the sagittal LS-NLD angle is expected to change as the skull develops, multiple studies have reported different values, suggesting substantial individual variation.

In a measurement based on 46 lacrimal pathways from 23 Japanese adult cadavers by Narioka et al., the sagittal LS-NLD angle was found to exhibit anterior inclination in approximately 80% of cases and posterior inclination in the remaining 20%.(22) In contrast, in a study by Park et al. involving measurements of 42 lacrimal pathways from 21 Japanese adult cadavers, approximately 90% of cases showed posterior inclination with an average angle of -10.3°.(23)

This study also explored the anatomical constraints associated with procedures involving a straight probe. When the SOR-LS-NLD angle is a positive value, it poses challenges for a straight probe passing through the bNLD due to interference from the SOR (Fig. 7). This interference was observed in 16 cases (25.0%) among CNLDO patients in this study, indicating the potential benefit of using a probe with a curved or bent tip for procedures in such cases. Additionally, 44 cases (68.8%) exhibited a SOR-LS-NLD angle as negative values, indicating the feasibility of passing the bNLD with a straight probe without the interference of the SOR.

In the current study, the mean LS length in children measured at 10.2 ± 2.4 mm, which is notably longer than the value observed in our previous research involving adults, where it was 8.9 ± 2.3 mm. This suggests the LS may undergo dilation due to prolonged obstruction in CNLDO patients. Meanwhile, the average bNLD length in children measured at 8.0 ± 2.5 mm, while in adults, it was 13.2 ± 2.7 mm. Our multivariate analysis indicated that bNLD length tends to increase with age and height, offering a reasonable explanation for the observed disparity (Supplementary information).

This study has several potential limitations. Firstly, it was conducted at a tertiary academic children's hospital, and the CNLDO patients included were those who had not responded to conservative therapy or local anesthesia probing at the institution before referral. This introduces a selection bias regarding the extent to which the measurements in this study align with the general anthropometric characteristics of CNLDO children. Secondly, the DCG images utilized in this study were acquired using a mobile X-ray system, which may not guarantee perfectly aligned coronal and sagittal planes, possibly affecting the precision of the measurements.

This study contributes important anthropometric data derived from DCG images in a Japanese population, shedding light on the diverse morphology of the lacrimal pathway in patients with CNLDO. The results emphasize the considerable variation in the morphology of the lacrimal drainage system among individuals. Moreover, it became evident that probing with straight probes was anatomically infeasible in certain CNLDO patients. This information is pivotal for advancing our comprehension of anatomical diversities in CNLDO patients, potentially impacting both diagnosis and treatment strategies.

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Supplementary Information

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Journal Publication

published 25 Jun, 2024

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Diversity in Lacrimal Pathway Morphology Among Japanese Patients with Congenital Nasolacrimal Duct Obstruction

Status:

Journal Publication

Version 1

Abstract

Figures

INTRODUCTION

METHODS

Patient Selection

DCG procedure

Investigated Parameters on DCG Images

Statistical Analysis

RESULTS

Breakdown

Sagittal LS-NLD angle

SOR-LS-NLD angle

bNLD length

LS length

SOR interference

Coronal LS-NLD angle

Coronal Medial-LS angle

DISCUSSION

CONCLUSION

References

Supplementary Files

Status:

Journal Publication

Version 1