Anatomic Characteristics of the Lacrimal Sac and Adjacent Bony Structures - A Computed Tomographic-Dacryocystography Study

doi:10.21203/rs.3.rs-3878895/v1

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Anatomic Characteristics of the Lacrimal Sac and Adjacent Bony Structures - A Computed Tomographic-Dacryocystography Study

https://doi.org/10.21203/rs.3.rs-3878895/v1

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Purpose To describe the anatomic characteristics of the lacrimal sac and its adjacent bone structures and to provide surgical recommendations for endoscopic dacryocystorhinostomy (EN - DCR) in Asians.

Methods This retrospective comparative study involved 118 sides with complete nasolacrimal duct obstruction and 83 unaffected sides. Computed tomographic - dacryocystography (CT-DCG) scans were performed before lacrimal surgery, and image reconstruction was used to obtain continuous 0.75-mm axial, coronal, and segmental sections for review. The morphology of the lacrimal sac and its relationship with adjacent bony structures were determined for measurement, as well as the obstructed location.

Results The height of the lacrimal sac was 12.99 ± 2.10 mm in this study. The operculum of the middle turbinate (OMT) was located vertically in the lower third of the lacrimal sac. Horizontally, the junction between the maxillary bone and the lacrimal bone (MB-LB) was close to, mostly (60.2%) posterior to, the lacrimal sac. The uncinate process was more frequently attached to the lacrimal bones (75.1%). The obstructions were generally located around the entrance of the nasolacrimal duct (NLD); however, some were placed higher, with 7.63% blocked not lower than the OMT. There was a negative correlation between the diameter of the lacrimal sac and the level of obstruction (r= -0.35, p < 0.01).

Conclusion In this study, the OMT and MB-LB can be served as the landmarks in EN - DCR. Partial uncinectomy should be performed in most cases. The obstructions were generally located around the entrance of the NLD, but some extreme individual variations strongly implies the importance of CT-DCG scanning before surgery.

Health sciences/Diseases/Eye diseases/Lacrimal apparatus diseases

Health sciences/Signs and symptoms/Eye manifestations

lacrimal sac

nasolacrimal duct obstruction

endoscopic dacryocystorhinostomy

Computed tomographic - dacryocystography

Nasolacrimal duct obstruction (NLDO) is a common condition that can cause excessive tearing and mucopurulent discharge in patients. Complications such as keratitis, severe corneal ulcers, acute dacryocystitis, or orbital cellulitis may occur due to chronic dacryocystitis if NLDO is not correctly diagnosed and treated appropriately ^{[1, 2]}. Although there is no consensus on the most effective technique for the management of NLDO, endoscopic dacryocystorhinostomy (EN -DCR) should be recognized as the preferred treatment option due to its relatively high success rate (81%-96%) and absence of facial scar^{[1, 3, 4]}. The key to achieving a successful EN -DCR is complete exposure of the lacrimal sac, and this requires a comprehensive understanding of the anatomy of the lacrimal drainage system, as well as the pertinent relationships between the lacrimal sac and adjacent intranasal bony structures prior to surgery. It is very necessary to deeply understand the surgical anatomy and individual variation before performing the surgery.

Computed tomography (CT) is widely accepted as a helpful measurement prior to EN -DCR. Previous studies using CT have described the unique characteristics of Asian populations in terms of the anatomy of the lacrimal sac fossa and its adjacent bony structures. such as the operculum of the middle turbinate (OMT), the junction between the maxillary bone and the lacrimal bone (MB-LB), the uncinate process (UP), and the agger nasi cell (AN cell)^[5–8]. Asians usually have thicker bones, shallower nasolacrimal duct lumens, and narrower intranasal structures, making surgery manipulation more difficult and requiring a comprehensive understanding of the anatomy of the lacrimal drainage system before surgery. It is crucial to emphasize that all these studies highlight the bony nature of the fossa of the lacrimal sac.

As we know, CT scans, although valuable in revealing bony structures, are limited in assessing the specific size and characteristics of the cystic structure of the lacrimal sac. However, it is this precise information that holds paramount importance for surgeons, guiding the exact location for incisions and the design of the ostium. With the aid of contrast agent, computed tomographic-dacryocystography (CT-DCG) not only can provides accurate location of the lacrimal drainage system but also offers valuable information about the pathologies and their specific locations^[9].

In our study, we performed CT-DCG in Asian patients diagnosed with primary acquired nasolacrimal duct obstruction (PANDO) before undergoing EN -DCR, capturing images on both the affected and unaffected sides. This approach allowed us to comprehensively describe the morphology of the lacrimal sac (e.g. height and width), the relationship between the lacrimal sac and its adjacent structures (the OMT, MB-LB, UP, AN cell) and the summary of the distribution of the obstructed points, shedding new light on the intricacies of this crucial anatomical area.

Demographics

A total of 201 eyes from 126 PANDO patients were enrolled in this study; 118 eyes from 99 patients were classified into Group A (90F/9M; mean age 56.64 ± 12.64 years) and 83 eyes from 83 patients were classified into Group B (68F/15M; mean age 57.04 ± 12.31 years). The age of the patient (p = 0.83) and the sex ratio (p = 0.07) were similar between the two groups. In Group A, the patients had been complaining of epiphora for a duration ranging from 0.25 to 40 years (median: 5 years). Of the 99 patients enrolled, 97 eyes in 81 patients were accompanied by chronic dacryocystitis. Table 1 provides the classification of lacrimal passage abnormalities and outlines the reasons for excluding 51 eyes.

Table 1

Detail information on enrollment of 252 eyes of 126 PANDO patients.
	Classification	Eyes	Proportion (%)
Group A	Complete obstructed in NLD	118	46.83
Group B	unaffected eyes	83	32.94
Excluded eyes	Obstructed in canaliculi	19	7.54
	Previous DCR surgery history	12	4.76
	Lacrimal cyst	6	2.38
	Functional epiphora	4	1.59
	rhinitis	4	1.59
	Trauma history	4	1.59
	Acute dacryocystitis	2	0.79
Group A = affected eyes in patients with complete nasolacrimal duct obstructed patients; Group B = unaffected eyes in patients with unilateral nasolacrimal duct obstructed patients; NLD: nasolacrimal duct.

The Morphology of the Lacrimal Sac

The morphology of the lacrimal sac was measured and summarized in Table 2. The mean height of the lacrimal sac was 12.99 ± 2.10 mm in all 201 eyes, 13.19 ± 2.05 mm in Group A and 12.70 ± 2.13 mm in Group B, with no statistically significant differences between the two groups (p = 0.98) (Table 2). The transverse lacrimal sac diameter in the IRL was 1.81 ± 0.73 mm in Group B and 6.55 ± 14.65 mm in Group A (p < 0.01*). Similarly, the transverse diameter of the lacrimal sac in the LRL was 2.02 ± 1.14 mm in Group A and 1.21 ± 0.58 mm in Group B (p < 0.01*). At the entrance to the NLD, there were no statistically significant differences between the two groups for transverse diameters (5.58 ± 0.77 mm in Group A versus 5.46 ± 0.87 mm in Group B; p = 0.30) or anteroposterior diameter (6.70 ± 1.05 mm in Group A versus 6.65 ± 1.09 mm in Group B; p = 0.85).

Table 2

Measurement of the lacrimal sac and nasolacrimal duct.
	Group A	Group B	p value
The height of lacrimal sac (mm)	13.19 ± 2.05	12.70 ± 2.13	0.10
The transverse diameter of NLD in LRL (mm)	5.58 ± 0.77	5.46 ± 0.87	0.29
The anteroposterior diameter of NLD in LRL (mm)	6.70 ± 1.05	6.65 ± 1.09	0.78
The transverse diameter of NLD lumen in LRL (mm)	2.02 ± 1.14	1.21 ± 0.58	< 0.01*
The transverse diameter of lacrimal sac in IRL (mm)	6.55 ± 14.65	1.81 ± 0.73	< 0.01*
The distance between the OMT and URL (mm)	8.42 ± 2.73	7.82 ± 2.80	0.13
The distance between the OMT and LRL (mm)	4.61 ± 2.82	5.11 ± 2.73	0.21
Group A: obstructed eyes of patients with unilateral or bilateral primary acquired nasolacrimal duct obstruction patients; Group B: unaffected eyes of patients with unilateral primary acquired nasolacrimal duct obstruction patients; NLD: nasolacrimal duct; LRL: the lower reference level; IRL: the intermediate reference level; URL: the upper reference level; OMT: operculum of the middle turbinate; *Significant statistical difference with p value < 0.05.

The location of the OMT

In our study, we evaluated the relative relationship between the OMT and the lacrimal sac in both the vertical and horizontal directions. In the vertical position of the 201 eyes, the OMT is typically inserted into the lateral wall of the nose in the lower third of the lacrimal sac, 8.18 ± 2.77 mm below the superior margin (URL) and 4.82 ± 2.79 mm above the bony nasolacrimal canal (LRL). We also sought to determine whether obstruction had an impact on the vertical arrangement of the OMT; however, no statistically significant differences were found between Group A and Group B (Table 2). In some cases, the OMT could even be equal to (5 cases; 2.49%) or below (4 cases; 2.00%) the LRL (Fig. 4).

In the horizontal direction, the OMT was commonly located anterior to the PLC (153/201 eyes), but posterior to the PLS (136/201 eyes). The distance between the OMT and the PLC was similar between the two groups (1.76 ± 2.35 mm in Group A vs 1.83 ± 2.18 mm in Group B; p = 0.83); however, the OMT was closer to the PLS in Group A (0.74 ± 2.39 mm) than in Group B (1.40 ± 2.03 mm; p = 0.04).

The position of the MB - LB

The anteroposterior relationship between the lacrimal sac and MB-LB was measured at the IRL level. In Group B, approximately 70% of cases showed the lacrimal sac in front of the MB-LB (58/83 eyes); however, the proportion decreased to 53.39% in Group A (63/118 eyes; p < 0.01*), with the posterior wall of the lacrimal sac predominantly behind the MB-LB.

The relative arrangement of the OMT and MB-LB was further evaluated; in both groups, the OMT was located posterior to the MB-LB more often than anteriorly (Group A: 77.97%; Group B: 77.11%; p = 0.89). Additionally, the distance between the OMT and MB-LB showed no statistically significant differences between the two groups (1.28 ± 2.24 mm in Group A vs 1.10 ± 1.90 mm in Group B; p = 0.56).

The Relationship between the Lacrimal Sac and the UP

The relative relationship between the lacrimal sac and the UP was determined at all three reference levels. In our study, 201 eyes were examined and it was revealed that there was no statistical difference between Group A and B at any of the reference levels. The UP was inserted mainly into the lacrimal (75.1%) or maxillary (23.9%) bone at the LRL. At the IRL, it was attached to the lacrimal (16.4%), maxillary (74.6%) or turbinal (9%) bone. In the URL, the UP was inserted primarily into the turbinal bone (69.2%)or the maxillary bone (29.9%). Our results, combined with previously published studies of the UP position, are summarized in Table 3.

Table 3

Comparison of the position of the UP in published CT scan reports and this study.
	Retrolacrimal	Lacrimal	Maxillary	Turbinal
URL
Fayet study (n = 77)	4 (5.2%)	4 (5.2%)	22 (28%)	47 (61%)
Woo study (n = 152)	0 (0%)	0 (0%)	35 (23%)	117 (77.0%)
Current study (n = 201)	0 (0%)	2 (1%)	60 (29.9%)	139 (69.2%)
IRL
Fayet study (n = 77)	4 (5.2%)	18 (23%)	43 (55.8%)	12 (15%)
Woo study (n = 152)	0 (0%)	17 (11.1%)	98 (64.5%)	37 (24.3%)
Current study (n = 201)	0 (0%)	33 (16.4%)	150 (74.6%)	18(9%)
LRL
Fayet study (n = 77)	25 (32%)	35 (45%)	17 (22%)	0 (0%)
Woo study (n = 152)	0 (0%)	122 (80.3%)	30 (19.7%)	0 (0%)
Current study (n = 201)	2(1%)	151 (75.1%)	48 (23.9%)	0 (0%)
URL: upper reference level; IRL: intermediate reference level; LRL: lower reference level.

The presence of Agger Nasi Cell

Out of the 201 eyes, 173 demonstrated the presence of an AN cell, resulting in an incidence rate of 86.07%. The typical images obtained from the observation of the AN cell using CT - DCG are shown in Fig. 2. In axial CT at the level of the common canaliculus, the AN cell is primarily located in the posterior nasal aspect of the lacrimal sac (Fig. 2A). In the classic images of the coronal plane, the AN cell is positioned slightly above and on the inner side of the lacrimal sac (Fig. 2B). From the sagittal plane perspective, the AN cell is located in the upper posterior aspect of the lacrimal sac (Fig. 2C).

The location of the obstruction

Of the 118 eyes in Group A, the average obstructed point was located 0.48 ± 3.42 mm below the LRL. Scatter plots in Fig. 5 showed the distribution of the obstructed point in the lacrimal drainage system in this study. They were further divided into three subgroups according to the level of IRL and LRL. Specifically, there were nine cases (7.63%) that were blocked equal to or greater than the OMT (obstructed in the upper lacrimal sac), 49 cases (41.53%) that were below the OMT but equal to or greater than the bony nasolacrimal canal (obstructed in the lower lacrimal sac) and 60 cases (50.85%) that were inferior to the entrance to the NLD (obstructed in the NLD). The average and range of distances between the obstructed point and the reference levels are listed in Table 4. Due to the anatomical variation of the OMT insertion, two special cases required deep consideration. In one case, the OMT, LRL, and obstructed point were observed in the same axial CT plane, and it was taken as NLD obstruction with great deliberation. In the other case, the contrast agent was cut off at the OMT level, but the position was 4.5 mm below the LRL. It was classified as NLD obstruction in this study.

Table 4

Location of the obstruction in obstructed patients of the nasolacrimal duct.
Classification	Numbers	Proportion (%)	Average distance (mm)	Range (mm)
Upper lacrimal sac obstruction	9	7.63	1.92 ± 2.13^*	0.00–6.00
Lower lacrimal sac obstruction	49	41.53	1.58 ± 1.60^&	0.00–6.00
Nasolacrimal duct obstruction	60	50.85	3.14 ± 1.80^#	0.75-9.00
^*the distance from the obstructed point in upper LS to the intermediate reference level (IRL); ^&the distance from the obstructed point in lower LS to the lower reference level (LRL); ^#the distance from the LRL to the obstructed point in nasolacrimal duct.

Furthermore, we examined the correlation between the obstructed level and the diameter of the lacrimal sac at the IRL. Interestingly, the scatter plot and Pearson’s correlation confirmed a negative correlation between the diameter of the lacrimal sac and the level of obstruction (r = -0.35, p < 0.01) (Fig. 6). This suggests that the lower obstructed location is correlated with a larger lacrimal sac diameter at the level of the OMT.

EN -DCR for Asians remains a challenging procedure for surgeons, since an adequate but safe osteotomy requires a comprehensive understanding of the shape and variation of the obstructed lacrimal passage system. In this study, the lacrimal sac and intranasal characteristics of PANDO patients were measured and summarized with the help of CT-DCG. The height and width of the lacrimal sac were measured, its position with respect to OMT, MB-LB and UP was determined, and the relationship between the lacrimal sac and these intranasal landmarks was described to define a safe scope for osteotomies among Asians. The distribution of the obstruction point in the lacrimal sac was also explored and a negative correlation was found between the lacrimal sac diameter and the obstructed level, revealing additional features of obstructions among Asian populations.

The average height of the lacrimal sac in our study was approximately 13mm, which was close to but slightly different from what was measured in Fayet’s study (12 mm) ^[5] or Woo’s study (11 mm) ^[6] in Asians. This discrepancy may be attributed to the research methodology employed, since the current study was conducted with CT-DCG instead of plain CT as in previous studies, and the contrast agent used in CT-DCG made the contours of the uppermost lacrimal sac more explicit. Furthermore, the CT machine we chose was equipped with ultrathin sections (0.75 mm), which allowed for more accurate data than the other two researches (3 mm). Furthermore, racial differences may have an impact on this value since our data was shorter than some previous studies, such as Rajak's work (16mm) among Causcians ^[10].

The width of the entrance of the NLD, either transversely or anteroposteriorly, was not statistically different between obstructed and unaffected eyes in the current study, according to some previous published researches^{[11, 12]}. This result strongly indicates that the bony anatomy may not be highly correlated with the etiology of PANDO. The width of the lacrimal sac, which was determined by the transverse diameter of the contrast agent in the IRL, was further investigated in this study. Compared to unaffected eyes, the width of the lacrimal sac was significantly increased in Group A. Prior studies have noted enlargement of the acrimal sac fossa and associated thickened periosteum and fibrosis in patients with chronic PANDO^{[13, 14]}. Whether the size of the lacrimal sac undergoes dynamic changes with the progression of chronic inflammation or if different etiologies lead to various developments remains a subject requiring further investigation.

In an effort to evaluate the relationship between the obstructed level and the diameter of the lacrimal sac, a negative correlation was observed. This suggests that the lower the obstruction is placed, the larger the width of the lacrimal sac may develop. This concept reminds us to consider whether the different positions of obstruction are caused by different pathologies or simply reflect the different PANDO courses. Future studies should be conducted to solve this problem.

The OMT, also known as the axilla of the middle turbinate, is accepted as a landmark to determine the position of the lacrimal sac during DCR. Traditionally, it was described as the upper limit of the sac since several studies indicated that only 0%-20% of the sac was located above the OMT ^[15]. However, as imaging technology develops, newer studies have found that a large part of the lacrimal sac (ranging from 4–10 mm) is located higher than OMT with racial disparities in level of positioning ^{[5, 6, 10, 16, 17]}. In our study, CT-DCG has also revealed that the OMT is located in the lower third of the vertical lacrimal sac, approximately 8 mm below the uppermost sac and 5 mm above the bony nasolacrimal canal. The precision of the numbers provided by preoperative imaging is essential for surgical planning, as bone removal during EN -DCR must include a degree of superior extension from the OMT to guarantee full exposure to the lacrimal sac. However, in some cases, the OMT insertion was identified as lower than or equal to the entrance of the NLD, signifying a 4.48% lacrimal sac positioned entirely superior to the OMT. Therefore, these anatomical variations of the OMT as a vertical landmark should be taken into account before each EN -DCR, emphasizing the importance of preoperative imaging to demonstrate the upper and lower limit of the lacrimal sac.

The maxillary line appeared as a curved mucosal eminence that has been reported to be another key intranasal landmark in EN -DCR, serving as the posterior limit in the horizontal incision of the nasal mucosa. Studies have indicated that the lacrimal sac is generally located lateral to the MB-LB suture line and the OMT is usually anterior to the MB-LB ^{[5, 18]}. However, this study showed some discrepancies. In approximately 70% of cases in Group B, the lacrimal sac was found to be positioned anterior to the MB-LB, although this proportion decreased to 53.39% for obstructed eyes. This might be due to the enlargement of the lacrimal sac secondary to the obstruction. Therefore, it can be deduced that while the posterior wall of lacrimal sac may occasionally be slightly posterior to the MB-LB, the majority of lacrimal sacs are anterior to the MB-LB. This implies that the MB-LB can be deemed a dependable posterior boundary of the ostium in the Asian population.

In addition, we explored the relationship between the OMT and adjacent structures such as the PLC, PLS, and MB - LB in the IRL. More than three-quarters of the cases had the OMT located anterior to the PLC, but with an average distance of less than 2mm, which was shorter than what Woo's study reported (3.8 mm)^[6]. In particular, in almost three-quarters of the cases, the OMT was found to be posterior to the PLS, which is contrary to its relative position to the PLC. In almost 3/4 of the cases, the OMT was posterior to the MB-LB. This result should remind us that the lacrimal sac is usually quite close to the OMT, mostly anterior to it. Therefore, the posterior edge of the ostium incision does not necessarily have to exceed the OMT in most cases.

The UP is an important intranasal structure adjacent to the lacrimal sac. Previous studies had varied opinions about whether uncinectomy is necessary or not during EN -DCR ^{[5, 19]}. This research investigated the attachment of UP, finding that it was connected to the lacrimal bone at the LRL in 75.1% of cases, a rate higher than in other races^[5], but which is consistent with certain Asian studies ^{[6, 16]}. This supports the idea that partial uncinectomy should be considered in Asian patients in most of the cases ^{[6, 16]}; meanwhile, the UP can also serve as a landmark to approach the lower part of the lacrimal fossa^[6].

In our study, we observed an AN cell incidence rate of 86%, aligning closely with this established range^{[8, 20, 21]}. Specifically, with the contrast agent, we examined the AN cell at the exact level of the common canaliculus, as well as our observations of the relationship between the lacrimal sac and the AN cell on the axial, coronal, and sagittal planes. This suggests that the AN cell may overlap with the upper part of the lacrimal sac. When performing EN -DCR, if it is necessary to fully open the lacrimal sac to the level of the common canaliculus, it may be necessary to open the AN cell. Further research is required to explore the overlap relationship between the AN cell and the upper part of the lacrimal sac, as well as its potential impact on EN -DCR surgery.

Using CT-DCG scans, this research studied the obstructed positions of all PANDO patients and found that the most common obstructed sites were around the entrance to the NLD, which is consistent with previous studies ^[22–24]. Individual variations in the levels of obstructions were also observed, with almost half of the obstructions occurring in the lacrimal sac, at a site higher than the entrance of the NLD. There were 7.63% of cases with obstructions located at or higher than the OMT, which is quite a high position in the nasolacrimal passage system. Furthermore, it was highlighted that a higher position of obstruction is usually associated with a shallower lacrimal sac, which can pose a challenge during surgery. Thus, it is essential to perform CT-DCG scans before the operation to identify the obstructed point and measure the length and width of the lacrimal sac, while observing the anatomical details of the adjacent structures. In this way, a personalized surgical plan can be created that is tailored to precise bony removal and adequate lacrimal exposure.

There are some limitations in our study. Firstly, the sample size of around 200 cases is not large enough to accurately reflect the variation in the position of the OMT, MB-LB, UP, and obstructed point. Secondly, this research did not include cases of obstruction above the lacrimal sac; future research could be more valuable if it could incorporate the blockage of the upper lacrimal passage obstructions.

In sum, this research offers a detailed analysis of the morphology of the lacrimal sac and its relationship with adjacent structures through the use of CT - DCG. The OMT, accepted as a vertical intranasal landmark in EN -DCR, is located in the lower third of the lacrimal sac on average, although some patients may have their lacrimal sac completely on top of the OMT. The MB-LB, which is situated boarding on and mostly posterior to the lacrimal sac, is an important safety landmark when manipulating the horizontal ostium, as it marks the posterior edge. In Asians, UP is connected to the lacrimal bone in the LRL in 75.1% of cases, indicating that partially uncinectomy should be considered in a large percentage of cases. Moreover, considering the individual variations in the position of the OMT and the obstructed point, conducting a preoperative examination using CT-DCG images proves highly beneficial for achieving a more precise and personalized EN -DCR. We are confident that lacrimal CT-DCG imaging enhances our understanding of surgical anatomy, especially in special cases such as patients with a history of previous surgery or trauma, those suspected of having a foreign body, or individuals with small lacrimal sacs.

Patient Enrollment

In this retrospective case-controlled study, records were collected from Chinese patients who underwent orbital CT - DCG scans before lacrimal surgery between January 2021 and June 2022. Inclusion criteria for this study included unilateral or bilateral PANDO. Exclusion criteria included acute dacryocystitis, canalicular obstruction, previous lacrimal surgeries, lacrimal cysts, functional epiphora, rhinitis, and secondary NLDO induced by tumor, trauma, sarcoidosis, or Wegener's granulomatosis. Two hundred and one eyes from 126 adult candidates (109 women and 17 men, with an average age of 57.79 ± 12.37 years) were enrolled, including 75 bilateral cases. The study was approved by the Ethics Committee of Eye and ENT Hospital of Fudan Universitry, all experiments were performed in accordance with relevant guidelines and regulations. All patients had provided their written informed consent to surgery and routine preoperative CT scan. Then they were divided into two groups: Group A (118 sides) included the affected eyes of patients with unilateral or bilateral primary acquired NLDO patients; and Group B (83 sides) included the unaffected eyes of patients with unilateral PANDO.

Computer Tomodensitometry - Dacryocystography Scan Method

The patients underwent a CT-DCG scan using a 128 slice dual source high resolution scanner (Siemens Somatom Definition Flash, Siemens, Germany). Contiguous 0.75mm axial sections of the orbits parallel to the bilateral infraorbitomeatal lines and coronal and sagittal scans were acquired using a bone window algorithm (width: 4000; level: 700). The patients were placed in a supine position and a plain CT scan was performed prior to any operative procedure. Subsequently, each canaliculus of the patient was probed and injected with ioversol (320mg/ml) as contrast agent, followed by a second CT scan 5 minutes later. After scanning, saline solution was injected into each canaliculus to remove ioversol.

Computer Tomodensitometry Scan Analysis

The axial sections were viewed from the lower to the upper levels. The parameters were examined at three different reference levels according to previous reports by Fayet^[5] and Woo^[6]. These levels included the lower reference level (LRL), which was the lowest section in which the lacrimal sac was turning into the nasolacrimal duct (NLD) (Fig. 1A); the intermediate reference level (IRL) was determined by the OMT, where the insertion of the middle turbinate (MT) into the lateral wall of the nasal fossa just began (Fig. 1B); the upper reference level (URL) was the highest section in which contrast agent was observed in the lacrimal sac (Fig. 1C). The schematic representations of each level are shown in Fig. 1D.

The parameters of the lacrimal sac were measured with respect to its length (the distance between URL and LRL) and width (the transverse diameter in IRL), as well as the width of the entrance of the NLD at the LRL level, consisting of the transverse and anteroposterior diameters of the bony nasolacrimal canal and the transverse diameter of the lumen of the NLD (Fig. 1A).

The relative position of the OMT with respect to the lacrimal sac was evaluated in both the vertical and horizontal directions. Vertically, the distance from the top of the lacrimal sac to the OMT was calculated as the distance between the URL and the IRL; the distance from the OMT to the entrance of the NLD was calculated as the distance between the IRL and the LRL. Horizontally, the relative position and distance from the OMT to the posterior lacrimal crest (PLC), the posterior wall of the lacrimal sac (PLS), and the MB-LB were evaluated in the IRL (Fig. 1E).

The location relationship between the UP and the lacrimal sac was evaluated at each of the three reference levels according to the previous classification method reported. As is previously reported, the UP can be classified into four categories^[5] (Fig. 1F): posterior to PLC (category 1), anterior to the PLC and posterior to the MB-LB (category 2), attached to the maxillary bone (category 3) or inserted into the lateral wall of the MT (category 4). Additionally, a comparison was made between our results and two previous studies.

Previous research has indicated a strong association between the UP and the AN cell. We conducted an investigation into the presence of the AN cell. We specifically focused on the common canaliculus region, following the methodology established by Soyka^[8]. We explored the existence of the AN cell within the axial, coronal, and sagittal planes, as depicted in Fig. 2.

In this study, the obstruction site was evaluated in group A and classified into three subgroups (Fig. 3): 1) upper lacrimal sac obstruction, in which the obstruction was located above or equal to the IRL; 2) lower lacrimal sac obstruction, where the obstruction was higher than or equal to the LRL, but below the IRL; 3) NLD obstruction, indicating that the obstruction was lower than the LRL.

Statistical analysis

The age of the patient and the measured values were expressed as mean value ± standard deviation. The gender distribution was compared using a χ2 test. All data was measured three times by the same observer and the average value was recorded for statistical analysis. The measurement results between the two groups were calculated with a Student’s t test or Wilcoxon-Mann-Whitney test, depending on whether the data were continuous or not. The correlation between the obstructed level and the transverse diameter of the lacrimal sac was calculated using Pearson's correlation. Statistical significance was considered with a p value < 0.05.

Author contributions The authors thank Y.W. and C.Z. for manuscript review; X.C. and Y.F. performed the measurement in CT scans. L. Z. and J.Q. assisted with the statistical analyses.

Data availability statement Data are available on reasonable request. The deidentified datasets used and/or analysed during the current study are available from the corresponding author on reasonable request.

Funding This work was financially supported by the National Natural Science Foundation of China (81700807).

Competing interests None declared.

Patient consent for publication Not applicable.

Ethics approval This study was approved by ethics committee of Eye and ENT Hospital of Fudan University.

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No competing interests reported.

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Anatomic Characteristics of the Lacrimal Sac and Adjacent Bony Structures - A Computed Tomographic-Dacryocystography Study

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Abstract

Figures

INTRODUCTION

RESULTS

Demographics

The Morphology of the Lacrimal Sac

The location of the OMT

The position of the MB - LB

The Relationship between the Lacrimal Sac and the UP

The presence of Agger Nasi Cell

The location of the obstruction

DISCUSSION

METHODS

Patient Enrollment

Computer Tomodensitometry - Dacryocystography Scan Method

Computer Tomodensitometry Scan Analysis

Statistical analysis

DECLARATIONS

REFERENCES

Additional Declarations

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