Pre-lacrimal window maxillary sinus surgery: a computed tomography analysis and classification

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Arch Craniofac Surg. 2025;26(4):141-146

Publication date (electronic) : 2025 August 20

doi : https://doi.org/10.7181/acfs.2025.0023

Mohammad Waheed El-Anwar^,1, Mohamed Kamel Alawady², Mohamed Alshawadfy¹, Mohamed Mohamed Rabea¹, Atef Hussein Elsayed¹

¹Department of Otorhinolaryngology-Head and Neck Surgery, Faculty of Medicine, Zagazig University, Zagazig, Egypt

²Department of Otorhinolaryngology, Faculty of Medicine, Al-Azhar University, Cairo, Egypt

Correspondence: Mohammad Waheed El-Anwar Department of Otorhinolaryngology-Head and Neck Surgery, Faculty of Medicine, Zagazig University, Zagazig 44519, Egypt E-mail: mwenteg1973@gmail.com

Received 2025 May 27; Revised 2025 June 20; Accepted 2025 August 17.

Abstract

INTRODUCTION

The pre-lacrimal window approach (PLWA) is an emerging technique for addressing lesions of the anterior wall and floor of the maxillary sinus. Simmen et al. [1] previously reported that PLWA is feasible in only two-thirds of their patients. This percentage appears to be higher in the Chinese population [2].

Endoscopic sinus surgery (ESS) is now among the most frequently performed otorhinolaryngologic procedures [3-5]. With advances in endoscopic technology, surgical equipment, and imaging modalities, ESS has extended beyond the nose to the paranasal sinuses (PNS) and adjacent areas [6,7]. Detailed imaging is essential for effective and safe ESS [8]. Computed tomography (CT) plays a crucial role in evaluating sino-nasal disease and defining the anatomy of the PNS and adjacent structures [6,7], which can vary significantly even between sides in the same individual.

The PLWA is considered a major advancement in ESS, as it preserves the nasolacrimal duct (NLD) and overcomes limitations of traditional approaches such as endoscopy-assisted me-dial maxillectomy and the Caldwell-Luc operation [9-11].

The PLWA is feasible only when a pre-lacrimal window (PLW) is present. Removal of the bony lacrimal duct canal assists medial retraction of the lateral nasal wall and is necessary in cases with a narrow PLW. Preoperative CT assessment is essential to determine the expected difficulty of the PLWA.

Therefore, the aim of the current study was to determine the various dimensions, measurements, and grading of the PLW.

METHODS

This retrospective analysis was conducted on 100 CT scans of the PNS, corresponding to 200 sides, at the Department of Otorhinolaryngology, University Hospitals, between March 2020 and January 2023. The study was approved by the Zagazig University Institutional Review Board (IRB No. 10969-19-7). Exclusion criteria included patients younger than 18 years, a history of trauma or surgery involving the PNS or skull base, congenital abnormalities, malignancies, or fibro-osseous lesions of the PNS.

All CT examinations were performed using a 64-slice CT scanner (LightSpeed Volume VCT, GE Medical System). The protocol utilized a 0.625 mm detector width, 0.5 mm reconstruction interval, and a 1.5 mm section width.

Axial images were obtained to cover the PNS. Subjects were scanned in the supine position, with the beam parallel to the hard palate, extending from the hard palate to the frontal sinus (glabella), using 130 kV and 150 mA/sec, with a scan time of 1.5 seconds. Examinations were conducted with a bone window setting of 3,000 Hounsfield units (HU), centered at 700 HU. A high-resolution algorithm was employed to enhance visualization of fine bony structures.

Multiplanar reconstructions with detailed views in the sagittal and coronal planes were generated for all subjects at a dedicated post-processing workstation (Advantage Windows Volume Share 4.5, GE Medical System). To avoid missing subtle findings, images were reviewed in a routine, standardized manner.

The width of the PLW was measured as the distance between the anterior wall of the maxillary sinus and the anterior border of the NLD. In accordance with Simmen et al. [1], these measurements were taken at the level of the anterior insertion of the inferior turbinate into the frontal process of the maxilla. The width of the NLD was also measured, as was the angle between the axis of the NLD and the hard palate (Fig. 1).

Fig. 1.

Measurements of parameters analyzed in this study. (A) The width of the pre-lacrimal window, defined as the distance between the anterior wall of the maxillary sinus and the anterior border of the nasolacrimal duct (NLD), and the width of the NLD. (B) The angle between the axis of the NLD and the hard palate.

Because the diameter of the endoscopes most commonly used in ESS is 4 mm, we classified the PLW and NLD widths as either below or above this threshold. Measurements were categorized into grades as follows: grade 1 (<4 mm), grade 2 (4–8 mm), and grade 3 (>8 mm) for both the PLW and NLD widths. The angle between the axis of the NLD and the hard palate was also classified into three grades: grade 1 (50°–60°), grade 2 (61°– 70°), and grade 3 (>70°). Statistical analysis was performed using the SPSS statistical software package (version 25; IBM Corp.). A p-value of less than 0.05 was considered statistically significant.

RESULTS

Among the 100 CT scans included (200 sides), there were 68 men (49%) and 32 women. The mean age was 35.27±11 years (range, 14–72 years), with a mean age of 32±6.2 years for men and 31.6±7 years for women.

The mean distance between the anterior wall of the maxillary sinus and the anterior border of the NLD (PLW) was 5.6±2.4 mm (range, 0–11.15 mm). The mean distance on the right side was 5.6±2.33 mm (range, 0–11.15 mm), and on the left side was 5.6±2.46 mm (range, 0–11.1 mm), with no significant difference between sides (t=0.0021, p=0.9983) (Table 1). The mean NLD width was 6.38±1.84 mm (range, 1–11 mm). The mean width on the right side was 6.35±1.74 mm (range, 1–9.7 mm), and on the left side was 6.38±1.94 mm (range: 1.3–11 mm), also without a significant difference between sides (t=0.0814, p=0.9353). The mean angle between the axis of the NLD and the hard palate was 68.65°±6.94° (range, 54°–82°). The mean angle on the right side was 68.6°±6.77° (range, 54°–83°), and on the left side was 68.7°±7.1° (range, 56°–85°), again without a significant difference between sides (t=0.072, p=0.9427) (Table 1).

Table 1.

Measurements on both sides

The mean PLW in men was 5.74±2.63 mm (range: 0–11.15 mm), and in women it was 5.34±1.8 mm (range, 1.5–9.1 mm), with no significant difference according to sex (t=0.8638, p=0.3898). The mean NLD width in men was 6.2±1.9 mm (range, 1–9.7 mm), and in women was 6.69±1.67 mm (range, 3.9–11 mm), with no significant sex difference (t=1.2488, p=0.2179). The mean angle between the axis of the NLD and hard palate in men was 69.4°±7.3° (range, 54°–83°), and in women was 66.97°±5.7° (range, 56°–78°), also without significant difference by sex (t=1.6588, p=0.1004) (Table 2).

Table 2.

Measurements in patients according to sex

All measured diameters were categorized into grades (Table 3): for the PLW, grade 1 (<4 mm) was observed in 22% of patients, grade 2 (4–8 mm) in 63%, and grade 3 (>8 mm) in 15%. For the NLD width, grade 1 (<4 mm) was found in 8%, grade 2 (4–8 mm) in 97%, and grade 3 (>8 mm) in 13% of patients. Regarding the angle between the axis of the NLD and the hard palate, grade 1 (50°–60°) was found in 10% of patients, grade 2 (61°–70°) in 48%, and grade 3 (>70°) in 42% (Table 3).

Table 3.

Grades (types) of pre-lacrimal dimensions

DISCUSSION

Surgical access to pathology of anterior wall and floor of maxillary sinus is challenging. A large medial meatal antrostomy (MMA) provides good exposure only to posterior and superior maxillary sinus and is often inadequate for lesions of the anterior wall and floor [8]. Planned approaches for disease in these regions include open procedures such as the Caldwell-Luc [12], lateral rhinotomy, midfacial degloving, or Denker’s approach [13], all of which can result in significant postoperative morbidity [14].

Although a large MMA allows visualization of the anterior maxillary wall with a 70° endoscope, stripping the sinus mucosa for extirpation of lesions such as inverted papilloma—requiring angled instruments—is not feasible through the MMA. Endoscopic medial maxillectomy and the canine fossa (Caldwell-Luc) approach [9] are alternative options but are associated with a higher risk of morbidity.

Zhou et al. [10,11] described the PLWA (in Chinese literature in 2007 and in English in 2013), advocating subperiosteal removal of the bony medial maxillary wall, including the bony lacrimal canal, while preserving lacrimal apparatus and inferior turbinate.

The PLWA preserves the NLD and overcomes limitations of traditional approaches such as endoscopy-assisted medial maxillectomy and the Caldwell-Luc operation to the anterior, lateral, inferior, and inferomedial maxillary sinus [15,16]. The PLWA provides access to all regions of the maxillary sinus while conserving the inferior turbinate and anterior maxillary wall maintaining the nasal physiological functions such as mucociliary clearance and regulation of humidity and temperature.

The endoscopic approach offers access to, or through, the PLW of the maxillary sinus. The PLW refers to the anteromedial aspect of the maxillary sinus, extending from the NLD posteriorly to anterior wall of the maxillary sinus. The medial wall of the pre-lacrimal recess (PLR) is formed by maxillary bone located between pyriform aperture and NLD, and extends from the nasal floor to the orbital floor. This bone can be removed during the PLWA [17].

The PLWA enables optimal visualization of the most difficult and challenging areas inside the maxillary sinus (anterior, lateral, inferior, and inferomedial areas) [16]. This can be achieved using a 0°-endoscope and straight instruments, with very low overall morbidity [18] and rapid mucosal recovery, while preserving normal physiological and nasolacrimal system function [16]. Additionally, in transnasal endoscopic surgery, the lateral aspect of the pterygoid fossa and infratemporal fossa can be accessed using the PLWA [18]. Despite its advantages, there are very few studies addressing CT assessment of the PLW. Therefore, in the present study, we analyzed anatomical variations in the dimensions of the PLR, including PLW width (the distance between the anterior wall of the maxillary sinus and the anterior border of the NLD), NLD width, and the angle between the axis of the NLD and the hard palate. These measurements provide important information for the surgeon prior to planning an endoscopic modified medial maxillectomy, and help determine how feasible a PLWA will be.

We found that the mean PLW width was 5.6±2.4 mm (range, 0–11.15 mm), the mean NLD width was 6.38±1.84 mm (range, 1–11 mm), and the mean angle between the axis of the NLD and the hard palate was 68.65°±6.94° (range, 54°–82°), with no significant differences between sides or according to sex. The wide ranges observed for both PLW and NLD widths highlight the importance of assessing and measuring these CT dimensions in patients with maxillary lesions.

Simmen et al. [1] first described the anteroposterior measurement of the medial wall of the PLR and found the average distance between the pyriform aperture and the anterior aspect of the NLD to be 4.24 mm (range, 0–11.62 mm), with no significant side differences. These results closely match our findings regarding the mean and range of PLW width. However, their study only used a single axial measurement at the level of insertion of the inferior turbinate into the frontal process of the maxilla [1].

Simmen et al. [1] also classified the PLW into three types reflecting the surgical complexity of the PLWA. In type I (distance 0–3 mm, 31.5%), the PLWA is only possible with NLD dislocation and significant bone removal. The window created by bone removal is small, allowing only limited access to the anterior wall of the maxillary sinus. In type II (distance 3–7 mm, 56%), the PLWA is feasible but still requires bone removal along with NLD dislocation; the window created can easily be closed with a soft tissue flap. In type III (distance >7 mm, 12.5%), the PLWA can be readily performed with minimal bone work, providing an excellent overview of the anterior wall and floor of the maxillary sinus with little effort [1].

In the current study, we chose to categorize the types of PLW below and above 4 mm, reflecting the typical diameter of the most commonly used endoscopes in ESS. The measurements reported by Simmen et al. [1] are similar to those found in our study. In our grading, grade 1 (<4 mm, requiring temporary NLD dislocation) was observed in 22% of patients, grade 2 (4–8 mm) in 63%, and grade 3 (>8 mm, typically permitting easier PLWA without NLD dislocation) in 15%.

Thus, in the present study, a PLW greater than 8 mm (type 1 PLW), which allows straightforward PLWA, was present in only 15% of maxillary sinuses. Limited access (4–8 mm) was possible in 63% of cases, but often necessitated NLD dislocation. In 22% of maxillary sinuses (<4 mm), the PLWA would be particularly challenging, requiring temporary displacement of the tear sac and a significant amount of bone removal.

Therefore, CT evaluation and grading of the PLW may assist the surgeon in predicting the feasibility and technical difficulty of the PLWA, anticipating the need for NLD displacement, and deciding whether to pursue this approach. These considerations should be emphasized to both rhinologic surgeons and radiologists as part of the CT assessment of maxillary lesions, particularly those involving the anterior part or recurrent cases. However, further studies are needed to evaluate the clinical impact of these CT measurements and grading systems on maxillary sinus surgery outcomes.

With regard to the angle between the axis of the NLD and the hard palate, our study is the first to describe this parameter. Previous studies evaluating the PLW using CT have reported measurements at specific points, but none have described this angle. The importance of this measurement lies in its ability to provide information about the PLW dimension from the inferior to the superior aspect, rather than at a single point. A wider angle corresponds to a wider PLW, thus increasing the accessibility of the PLWA.

As for NLD width, we measured and graded this parameter to allow the surgeon to preoperatively assess the potential benefit of posterior displacement of the NLD and bone removal when the PLW is narrow. Removal of the bony lacrimal duct canal can facilitate medial retraction of the lateral nasal wall and is necessary in cases with a narrow PLW.

In summary, measuring the PLW width, NLD width, and the angle between the axis of the NLD and the hard palate appears helpful for assessing the feasibility of the PLWA and should be considered during preoperative planning. Increasing awareness and utilization of these measurements among rhinologic surgeons and radiologists will likely be beneficial. Nevertheless, the impact of these parameters on surgical outcomes requires further investigation.

The limitations of this study include the need to evaluate these dimensions in different ethnic groups and to apply the new measurements and classification systems in operative settings. Future studies are therefore recommended to address these aspects.

In conclusion, inclusion of CT dimensions of the PLW should be considered when planning endoscopic approaches to or through the anterior aspect of the maxillary sinus. The present study enhances the awareness of surgeons and radiologists regarding PLW measurements and variations, ultimately improving the application of the PLWA.

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