Beyond direct visualization: a comparative analysis of computed tomography dacryocystographic features in dacryolithiasis, lacrimal sac cysts, and primary acquired nasolacrimal duct obstruction

Introduction

Nasolacrimal duct obstruction (NLDO) encompasses a spectrum of disorders affecting the lacrimal drainage system, with various etiologies including inflammatory, traumatic, and idiopathic causes (1). Among these, dacryoliths, also known as lacrimal stones or mucopeptide concretions, represent a distinct but relatively uncommon pathology, reported in approximately 5.8–18% of patients undergoing dacryocystorhinostomy (DCR) (2-4). Clinical manifestations of dacryoliths often mirror those of other lacrimal drainage disorders, presenting with epiphora, chronic dacryocystitis, and recurrent infections (5). However, unlike primary acquired nasolacrimal duct obstruction (PANDO), which may be managed with less invasive procedures such as silicone stent placement in some cases, dacryoliths invariably require surgical removal for definitive treatment (3). The challenge lies in their preoperative identification, as conventional diagnostic methods, including irrigation and probing, may not definitively distinguish dacryoliths from other causes of obstruction.

Computed tomography dacryocystography (CT-DCG) has emerged as a valuable diagnostic tool in the evaluation of lacrimal drainage system disorders, offering detailed anatomical visualization and the potential to differentiate various pathologies (6). Traditional imaging studies have characterized dacryoliths as round or oval filling defects on dacryocystography, occasionally displaying a peripheral rim of calcification that creates a distinctive “rice kernel” appearance (3,7); however, the comprehensive radiological characteristics that distinguish dacryoliths from other causes of NLDO remain incompletely understood. Despite the widespread adoption of CT-DCG in clinical practice, there remains a notable paucity of systematic analyses examining the specific imaging features that might reliably predict the presence of dacryoliths and differentiate them from other lacrimal drainage system pathologies, underscoring the need for more refined radiological parameters, particularly given the potential impact of accurate preoperative diagnosis on surgical planning and patient management.

The relationship between dacryoliths and concurrent lacrimal sac pathology remains an area of significant interest in the field. Several studies have reported that patients with dacryoliths often present with enlarged lacrimal sacs on dacryocystography (4,5), suggesting a potential association between sac morphology and stone formation. However, whether this anatomical variation represents a predisposing factor for dacryolithiasis or develops secondary to the stone’s presence remains unclear. To better understand these relationships, we conducted a comparative analysis of CT-DCG findings between patients with dacryoliths, dacryocysts (characterized by enlarged lacrimal sacs), and PANDO, aiming to identify distinctive imaging patterns among these entities.

In this retrospective study, we analyzed the CT-DCG characteristics of 18 patients with surgically confirmed dacryoliths, comparing their imaging features with those of patients diagnosed with lacrimal sac cysts and PANDO. Our primary objectives were to (I) identify specific radiological patterns that might distinguish dacryoliths from other causes of lacrimal drainage system obstruction, (II) evaluate the relationship between lacrimal sac morphology and the presence of dacryoliths, and (III) establish potential imaging criteria that could improve the preoperative diagnosis of dacryolithiasis. By elucidating these distinctive radiological features, we aim to enhance the diagnostic accuracy of CT-DCG and optimize surgical planning for patients with lacrimal drainage system disorders. We present this article in accordance with the STROBE reporting checklist (available at https://qims.amegroups.com/article/view/10.21037/qims-2024-2971/rc).

Methods

Study design and patient selection

This retrospective case-control study was conducted through the analysis of medical records from patients who underwent preoperative orbital CT-DCG followed by DCR between December 2020 and November 2024. All 515 patients who underwent DCR during this period received preoperative CT-DCG as part of our standard evaluation protocol. Cases were excluded if canalicular obstruction, functional epiphora, chronic rhinitis, or secondary NLDO due to neoplasms, trauma, sarcoidosis, or granulomatosis with polyangiitis were present. During this 4-year period, 515 DCR procedures were performed, from which 18 cases of intraoperatively confirmed dacryoliths were identified. For comparative analysis, 18 patients with lacrimal sac cysts and 18 patients with PANDO were consecutively enrolled. The study was conducted in accordance with the tenets of the Declaration of Helsinki and its subsequent amendments and was approved by the Institutional Ethics Committee of Eye, Ear, Nose, and Throat Hospital of Fudan University (No. 2023164). The requirement for individual informed consent was waived owing to the retrospective nature of the study.

Protocol of CT-DCG

All CT-DCG examinations were performed on a 128-slice dual-source high-resolution scanner (SOMATOM Definition Flash, Siemens Healthineers, Erlangen, Germany). Images were acquired with patients positioned supine, with 0.75-mm contiguous axial sections being aligned parallel to the infraorbitomeatal line. A bone window algorithm [width: 4,000 Hounsfield units (HU); level: 700 HU] was applied, and the scanning range encompassed the region from the superior orbital rim to the inferior margin of the maxillary sinus.

The imaging protocol consisted of two phases. Initially, a baseline noncontrast scan was obtained. Prior to contrast administration, the lacrimal drainage system was thoroughly irrigated with saline solution to clear any easily removable secretions. Subsequently, ioversol contrast medium (320 mg I/mL) was gently irrigated into each canaliculus, followed by a post-contrast scan after a 5-minute delay to evaluate contrast distribution throughout the lacrimal drainage system.

CT-DCG image analysis

All CT-DCG images were evaluated by an experienced orbital radiologist with more than 10 years of expertise in lacrimal system imaging. For standardized assessment, the largest cross-sectional area of the lacrimal sac was identified on axial images, where the transverse diameter was measured at the maximum width of contrast enhancement, and the anteroposterior (AP) diameter was measured perpendicular to it (Figure 1A). The vertical length was determined by measuring the distance between the superior extent of contrast enhancement and the bony transition from the lacrimal sac to the nasolacrimal duct, which was defined by the appearance of a complete bony ring. At the level of maximum lacrimal sac dilation, contrast distribution patterns were analyzed via measurements of the depth of the fluid level and the calculation of the filling ratio [(depth of fluid level/total sac depth) ×100%], while the presence of filling defects was documented (Figure 1B). Additional imaging features were systematically recorded (Figure 1C-1F), including peripheral rim calcification (demonstrated as bright white outlines around the sac margin), superior air bubbles (visible as dark areas in the superior portion of the sac), lateral wall enhancement patterns, and a distinct density interface line delineating two different contrast densities within the lacrimal sac. This last feature, as illustrated in Figure 1F (white arrow), appears as a clear straight line dividing two regions of different radiographic densities within the same sac—a unique finding that suggests the coexistence of two distinct fluid compositions or contrast concentrations within the lacrimal sac.

Figure 1 Representative CT-DCG images demonstrating characteristic features and measurement methods. (A) Measurement methodology: red single-headed arrows clearly delineate the lacrimal sac boundary; the black horizontal double-headed arrow indicates the maximum transverse diameter measured at the widest point of contrast enhancement; the black vertical double-headed arrow shows the AP diameter measured perpendicular to the transverse axis; the red double-headed arrow demonstrates the vertical height of the contrast fluid level within the sac. (B-F) Characteristic imaging features: (B) surface filling defect (white arrow) at the contrast-air interface. (C) Peripheral calcification (white arrow) along the sac wall. (D) Superior air bubble (white arrow). (E) Lateral wall enhancement (white arrow). (F) Density interface line (white arrow) within the contrast-filled sac. AP, anteroposterior; CT-DCG, computed tomography dacryocystography.

Intraoperative assessment

All surgical procedures were performed by a single experienced surgeon using the standard endoscopic DCR technique. During surgery, dacryoliths were characterized based on their anatomical location (categorized as lacrimal sac, nasolacrimal duct, or combined sac-duct involvement), morphological pattern (spherical/ovoid versus irregular configuration), and surgical visualization (readily identifiable versus requiring extended exploration) (Figure 2). The presence and degree of associated inflammation were documented as copious purulence, minimal purulence, or absence of purulent material. All procedures were video-recorded to enable the subsequent verification of intraoperative findings. The excised lacrimal sac specimens were fixed in 10% neutral buffered formalin, processed routinely, and stained with hematoxylin and eosin (HE) and periodic acid-Schiff (PAS) for histopathological examination.

Figure 2 Intraoperative endoscopic findings of dacryoliths during DCR surgery. (A) Oval dacryolith visible within the lacrimal sac after initial exposure. (B) Combined dacryolith traversing both the lacrimal sac and nasolacrimal duct. (C) Irregular dacryolith extending from the nasolacrimal duct. (D) Multiple round dacryoliths in aggregate formation encountered during surgical exploration. DCR, dacryocystorhinostomy.

Statistical analysis

Statistical analyses were performed with SPSS software version 20.0 (IBM Corp., Armonk, NY, USA). Continuous variables are expressed as the mean ± standard deviation (SD) or as the median with interquartile range (IQR) based on their distribution pattern as assessed by the Shapiro-Wilk test. Categorical variables are presented as frequencies and percentages. For comparisons between the three groups (dacryoliths, lacrimal sac cysts, and PANDO), one-way analysis of variance (ANOVA) with Holm-Bonferroni post hoc correction was applied for normally distributed continuous variables, while the Kruskal-Wallis test followed by Mann-Whitney U tests with Holm-Bonferroni adjustment was applied for nonnormally distributed data. Categorical variables were analyzed with the Fisher exact test due to the relatively small sample sizes. The radiological characteristics on CT-DCG were compared between groups via the Fisher exact test. All statistical tests were two-tailed, and a P value <0.05 was considered statistically significant.

Results

Demographic characteristics

Between December 2020 and November 2024, a total of 515 patients who underwent endoscopic DCR were reviewed, among whom 18 were found to have dacryoliths during surgery, yielding a prevalence of 3.5%. For comparative analysis, 18 patients with lacrimal sac cysts and 18 patients with PANDO were consecutively enrolled. As shown in Table 1, demographic characteristics including age, sex distribution, laterality, history of lacrimal intubation, and duration of epiphora were comparable among the three groups (all P values >0.05).

Intraoperative findings in dacryolith cases

During surgery, dacryoliths were identified at various anatomical locations within the lacrimal drainage system. As detailed in Table 2, dacryoliths were most frequently located in either the lacrimal sac alone (44.44%) or both the sac and duct (combined sac-duct involvement) (44.44%), while nasolacrimal duct was the least common location (11.11%). Regarding morphological patterns, irregular configurations predominated (61.11%) over spherical/ovoid shapes (38.89%). While the majority of dacryoliths (88.89%) were readily identifiable during surgery, two cases required extended exploration due to superior location, with stones being discovered only during sac cavity debridement and subsequent aspiration. Associated inflammation was present in nearly all cases, with copious purulence observed in 55.56% of cases. Histopathological examination of excised lacrimal sac specimens revealed intensely PAS-positive staining in 7 (38.89%) cases.

Lacrimal sac morphology on CT-DCG

Lacrimal sac dimensions showed varying patterns across the three groups (Table 3). Although the vertical height was slightly greater in the dacryolith group (15.31±2.39 mm) as compared to that in the lacrimal sac cyst (13.67±2.89 mm) and PANDO (13.74±1.66 mm) groups, this difference did not reach statistical significance (P=0.08). Both maximum transverse and AP diameters demonstrated significant differences between groups (P<0.01 and P=0.01, respectively). Post hoc Bonferroni analysis revealed that these differences were primarily attributed to the enlarged dimensions in the lacrimal sac cyst group, while comparisons between dacryolith and PANDO groups showed no significant differences (transverse diameter: P=0.14; AP diameter: P=0.85). Although the absolute fluid level height varied across groups (P=0.02), the fluid level ratio emerged as a more discriminative parameter, with significant differences observed between all paired group comparisons (all P values <0.01). These characteristic patterns of fluid distribution are illustrated schematically in Figure 3. In addition, all patients who underwent DCG also underwent CT, and out of the 18 with dacryoliths on DCG, only 5 (27.8%) had detectable dacryoliths on CT.

Figure 3 Schematic representation and corresponding CT-DCG images of the contrast distribution patterns in three study groups. Group 1 (dacryolith): (A) schematic drawing showing moderate contrast filling (red) with stone presence (yellow) and (B) the corresponding CT-DCG image demonstrating surface filling defects (red arrows). Group 2 (lacrimal sac cyst): (C) schematic illustration depicting minimal contrast filling limited to the inferior sac and (D) the representative CT-DCG image. Group 3 (PANDO): (E) schematic diagram showing near-complete contrast filling of lacrimal sac and (F) the corresponding CT-DCG image demonstrating a characteristic complete filling pattern. CT-DCG, computed tomography dacryocystography; PANDO, primary acquired nasolacrimal duct obstruction.

Distinctive imaging features on CT-DCG

Analysis of CT-DCG images revealed several characteristic patterns among the groups (Table 3). Irregular fluid–air interfaces were most frequently observed in the dacryolith group (14/17, 82.4%), while such surface filling defects were less common in the lacrimal sac cyst group (4/15, 26.7%) and rarely seen in PANDO cases (1/18, 5.6%) (P<0.01). Peripheral calcification, although not a universal finding, was predominantly detected in the dacryolith group (11/17, 64.7%), with only one case observed in the lacrimal sac cyst group (1/16, 6.3%) and none in the PANDO group (P<0.01). A distinctive density interface line was identified in a subset of dacryolith cases (4/17, 23.5%) but was absent in both other groups (P=0.03). Lateral wall enhancement showed similar frequencies between the dacryolith (7/17, 41.2%) and lacrimal sac cyst (7/16, 43.8%) groups, while the presence of superior air bubbles demonstrated no significant differences among groups (P=0.31).

Discussion

This study systematically analyzed the CT-DCG characteristics of dacryoliths in comparison with lacrimal sac cysts and PANDO, establishing distinctive imaging patterns for differential diagnosis. The fluid level ratio emerged as a critical discriminative parameter, with dacryoliths showing characteristic moderate filling patterns (63.30%±20.43%) that differed significantly from both the minimal filling in lacrimal sac cysts (29.44%±11.77%) and the near-complete filling in PANDO (80.14%±15.46%). This moderate fluid accumulation, particularly when accompanied by surface filling defects, peripheral calcification, or distinctive density interface lines, strongly suggests the presence of dacryoliths. The high frequency of positive PAS staining (38.89%) in dacryolith cases suggests a potential role of fungal infection in stone formation. Although all mucopeptide concretions would be expected to show some degree of PAS positivity due to their composition, the specimens from these cases demonstrated intensely PAS-positive fungal hyphae and spores against the background of PAS-positive mucopeptide material, suggesting a pattern of fungal colonization described in a previous study (8).

These findings have important clinical implications. It should be noted that the prevalence of dacryoliths in our series (3.5%) appears lower than the previously reported rates of 5.8–18% in the literature (2-4). This discrepancy likely reflects our strict inclusion criteria, as we only included cases where stones were directly visualized during DCR surgery. Cases involving canalicular stones (9) were excluded as they typically do not require DCR, and stones located in Hasner’s valve region (10) might have been underrepresented due to the standard surgical approach not extending to such inferior positions.

Unlike sialoliths or rhinoliths, which are predominantly composed of inorganic calcium compounds, lacrimal stones are characteristically softer and primarily composed of organic materials, particularly mucopeptides and trefoil factor family peptides (11-13). This compositional difference explains why individual CT-DCG features of dacryoliths demonstrate relatively low detection rates in our study—peripheral calcification was observed in only 64.7% of cases, and density interface lines were present in just 23.5%. The pathogenesis involving initial epithelial injury and subsequent accumulation of organic materials (14,15) results in stones that may not be as radiologically distinct as their counterparts in other organs. Therefore, our findings emphasize the importance of considering multiple imaging features in combination, particularly the characteristic moderate fluid level ratio and surface filling defects, as no single radiological sign appears to be sufficiently sensitive for definitive diagnosis.

The distinctive fluid level ratios observed across the three groups reflect their underlying pathophysiological characteristics. In lacrimal sac cysts, the markedly low filling ratio (29.44%±11.77%) can be attributed to the presence of viscous mucoid contents that resist contrast agent penetration, resulting in large non-enhancing cavities. Conversely, PANDO cases demonstrated the highest filling ratios (80.14%±15.46%), as the contrast agent readily permeates the inflamed but otherwise empty sac lumen. The intermediate filling ratio observed in dacryolith cases (63.30%±20.43%) appears to result from the partial luminal occupation by the stones themselves, creating characteristic filling patterns. These distinct ratio patterns, reflecting the underlying pathological conditions, make the fluid level ratio a particularly valuable diagnostic indicator for differentiating between these entities on CT-DCG.

Our intraoperative findings highlight important considerations for surgical technique. Although most dacryoliths (88.9%) were readily identifiable during surgery, the identification of two cases where stones were initially overlooked due to their superior location underscores the importance of thorough surgical exploration. In these two cases, the stones were initially overlooked and were only discovered accidentally during lacrimal irrigation, when they were flushed out from their superior location. This unexpected finding underscores the importance of thorough surgical exploration. These cases specifically point to the need for adequate superior extension of the osteotomy and meticulous examination of the entire lacrimal sac, particularly its superior aspect, to avoid superiorly located stones being missed. This observation has direct implications for surgical planning. When CT-DCG demonstrates characteristic moderate filling patterns with surface irregularities or peripheral calcification, surgeons should do the following: (I) create a sufficiently high osteotomy to access the superior lacrimal sac; (II) conduct systematic exploration of the entire sac cavity, with particular attention to superior recesses; (III) consider gentle irrigation to dislodge hidden stones; and (IV) be prepared to manage associated infection given the high prevalence of purulent material in dacryolith cases. To standardize implementation in clinical practice, we recommend a structured CT-DCG interpretation approach that emphasizes the assessment of filling patterns and calcification markers, with consistent communication between radiologists and surgeons being applied to address the potential variability in imaging interpretation.

Several limitations of this study should be acknowledged. First, the retrospective design inevitably introduced selection bias; however, mitigation strategies, including comprehensive electronic record searches with multiple codes, independent case review by two investigators, and exclusion of cases with incomplete documentation, were implemented. Although our cohort study represents one of the larger dedicated CT-DCG series of dacryoliths, the relatively low prevalence of this condition (3.5% in our series) necessitated a 4-year collection period at our high-volume center to attain the sample size examined, but nevertheless constrains the broader applicability of our results. Second, the sensitivity and specificity of identified CT-DCG patterns could not be determined due to the study design. A prospective multicenter approach would provide stronger evidence and is currently being planned. Third, our pathological analysis was limited to lacrimal sac specimens, as dacryoliths were aspirated during surgery rather than preserved for examination. Additionally, comprehensive histopathological comparison across all three groups was not performed. We have since implemented a tissue-banking protocol to enable future comparative analyses. Future prospective studies with larger cohorts, standardized imaging protocols, and comprehensive pathological examination of both lacrimal sac tissue and intact dacryoliths are needed to validate these findings and establish more definitive diagnostic criteria.

Conclusions

This study established distinctive CT-DCG imaging patterns for differentiating dacryoliths from lacrimal sac cysts and PANDO. The moderate fluid level ratio (approximately 63%), especially when combined with surface irregularities, peripheral calcification, or density interface lines, provides a valuable diagnostic signature for dacryoliths. These imaging characteristics reflect the unique pathophysiology of dacryoliths and have direct implications for surgical planning, particularly the need for adequate superior extension of osteotomy and thorough exploration of the entire lacrimal sac. Although no single radiological feature demonstrated sufficient sensitivity for definitive diagnosis, the combination of moderate fluid filling and associated features offers improved preoperative recognition. Implementation of these findings into clinical practice could enhance diagnostic accuracy, optimize surgical approaches, and ultimately improve patient outcomes. Future prospective multicenter studies with standardized protocols are warranted to validate these findings and establish definitive diagnostic criteria for dacryoliths.

Acknowledgments

None.

Footnote

Reporting Checklist: The authors have completed the STROBE reporting checklist. Available at https://qims.amegroups.com/article/view/10.21037/qims-2024-2971/rc

Funding: None.

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://qims.amegroups.com/article/view/10.21037/qims-2024-2971/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. This study was conducted in accordance with the tenets of the Declaration of Helsinki and its subsequent amendments and was approved by the Institutional Ethics Committee of Eye, Ear, Nose, and Throat Hospital of Fudan University (No. 2023164). The requirement for individual informed consent was waived owing to the retrospective nature of the study.

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/.

References

1. Ali MJ. Etiopathogenesis of primary acquired nasolacrimal duct obstruction (PANDO). Prog Retin Eye Res 2023;96:101193. [Crossref] [PubMed]
2. Yazici B, Hammad AM, Meyer DR. Lacrimal sac dacryoliths: predictive factors and clinical characteristics. Ophthalmology 2001;108:1308-12. [Crossref] [PubMed]
3. Khorrami Kashi A, Keilani C, Nguyen TH, Keller P, Elahi S, Piaton JM. Dacryolithiasis diagnosis and treatment: a 25-year experience using nasal endoscopy. Br J Ophthalmol 2023;107:289-94. [Crossref] [PubMed]
4. Komínek P, Červenka S, Zeleník K, Pniak T, Tomášková H, Matoušek P. Lacrimal sac dacryolith (76 cases): a predictive factor for successful endonasal dacryocystorhinostomy? Eur Arch Otorhinolaryngol 2014;271:1595-9. [Crossref] [PubMed]
5. Mishra K, Hu KY, Kamal S, Andron A, Della Rocca RC, Ali MJ, Nair AG. Dacryolithiasis: A Review. Ophthalmic Plast Reconstr Surg 2017;33:83-9. [Crossref] [PubMed]
6. Cui X, Wang Y. Assessing the relationship of agger nasi pneumatization to the lacrimal sac: a dynamic computed tomography-dacryocystography analysis. Quant Imaging Med Surg 2024;14:5642-9. [Crossref] [PubMed]
7. Asheim J, Spickler E. CT demonstration of dacryolithiasis complicated by dacryocystitis. AJNR Am J Neuroradiol 2005;26:2640-1. [PubMed]
8. Perry LJ, Jakobiec FA, Zakka FR. Bacterial and mucopeptide concretions of the lacrimal drainage system: an analysis of 30 cases. Ophthalmic Plast Reconstr Surg 2012;28:126-33. [Crossref] [PubMed]
9. Zhang H, Xu M, Qin G, Chen J, Qi Y, Xu L, He W, Pazo EE. Asymptomatic stones in the lacrimal canaliculus. Clin Case Rep 2023;11:e8175. [Crossref] [PubMed]
10. Huo Y, Li L, Mo Y, Guo S. A case report of chronic dacryocystitis caused by nasal stones. BMC Ophthalmol 2023;23:445. [Crossref] [PubMed]
11. Komínek P, Doškářová S, Svagera Z, Lach K, Cervenka S, Zeleník K, Matoušek P. Lacrimal sac dacryoliths (86 samples): chemical and mineralogic analyses. Graefes Arch Clin Exp Ophthalmol 2014;252:523-9. [Crossref] [PubMed]
12. Kally PM, Omari A, Schlachter DM, Folberg R, Nesi-Eloff F. Microbial profile of lacrimal system Dacryoliths in American Midwest patient population. Taiwan J Ophthalmol 2022;12:330-3. [Crossref] [PubMed]
13. Díaz YM, Galindo-Ferreiro A, Akaishi PM. Dacryoliths causing intermittent epiphora associated with a patent lacrimal system. Arq Bras Oftalmol 2016;79:411-3. [Crossref] [PubMed]
14. Ali MJ, Scholz M, Singh S, Heichel J, Paulsen F. Etiopathogenesis of lacrimal sac mucopeptide concretions: insights from cinematic rendering techniques. Graefes Arch Clin Exp Ophthalmol 2020;258:2299-303. [Crossref] [PubMed]
15. Ali MJ, Heichel J, Paulsen F. Dacryolithogenesis or Dacryolithiasis-The Story So Far. Ophthalmic Plast Reconstr Surg 2024;40:30-3. [Crossref] [PubMed]