Larger Osteotomies Result in Larger Ostia in External Dacryocystorhinostomies FREE

The key to success in dacryocystorhinostomy (DCR) is in creating a large enough passage between the nasolacrimal sac and the nasal mucosa that will remain patent after surgery. A meticulous dissection, including careful opening of the nasolacrimal sac and incising the mucosa of the nasolacrimal duct, is a requirement for surgical success. Removal of the lacrimal bone and lacrimal process of the maxillary bone is also required in most cases. Intraoperative osteotomy is only 1 factor that contributes to success, and scar formation may be an equally important factor in determining surgical outcome.¹ Additional elements that influence outcome include small size and inappropriate position of the osteotomy as well as extension of the ethmoid air cells medial to the lacrimal sac.¹

Although the extent of bone removal in DCR is controversial, “the more the better” is a common belief. The first study that examined postoperative ostia was conducted in 1982 by Linberg et al,² who used a rigid endoscope. The authors found no correlation between the sizes of the osteotomy created during DCR and the final ostium size. The purpose of the current study was to measure final ostium size by means of nasal endoscopy and the functional endoscopic dye test (FEDT)³ with the use of image analysis software in patients undergoing external DCR surgery in order to examine whether there is any correlation between the primary osteotomy created during surgery and the final ostium size and to evaluate whether surgical outcome is influenced by these 2 factors.

This prospective nonrandomized study included all consenting consecutive patients with acquired nasolacrimal duct obstruction who underwent external DCR at the Royal Victorian Eye and Ear Hospital, Melbourne, Australia. Institutional review board approval was obtained to conduct the study. All participants signed an informed consent.

External DCR was performed in a standard fashion in all patients. A bony window, which included the anterior lacrimal crest, the lacrimal fossa, and the superior aspect of the nasolacrimal duct, was created using a rongeur. During surgery, the bone opening was measured in the anterior posterior and superior inferior axes with a millimeter ruler. The intraoperative osteotomy surface area was calculated by multiplying osteotomy height and width in millimeters. Anterior and posterior mucosal flaps were fashioned in the lacrimal sac and the nasal mucosa and sutured over a silicone tube using a 6-0 polyglactin suture. Success was defined as a resolution of symptoms and a lack of tearing, with a positive FEDT result.

All patients underwent endonasal endoscopy to evaluate the ostium size and surgical outcome 3 months after surgery. The intranasal ostium was photographed together with a 3-mm-diameter curette. The FEDT was performed by instilling fluorescein eyedrops and demonstrating the dye in the nose at the ostium (Figure 1). Normally, the dye would appear within seconds from instillation after several blinking cycles. Cases of late appearance (several minutes) were noted. Failure to demonstrate fluorescein in the nose was defined as a failed FEDT result.

Photographed images were scanned to digital images and analyzed using Image Pro Plus version 4.5 (Media Cybernetics, Bethesda, Maryland). The best-fit circle method was used to measure the curette size in pixels (Figure 2). Because postoperative ostia were generally ellipsoid, the surface area in pixels was determined by summing the areas of 2 arcs (Figure 2). If feasible, the best-fit circle method was applied to ostia as well. The ratio between ostium area to curette area was calculated and multiplied by the true known curette area in square millimeters.

The arc surface area was calculated by subtracting the triangle limited by the circle radius and angle (using Image Pro Plus computer software) from the sector area (with known radius and angle dimensions) (Figure 3). The total ostium area was calculated by summing the 2 arc surface areas. The arc method was applied for calculating curette surface in cases in which the best-fit circle method was not feasible. The area of a circle was calculated as the radius of the circle squared (multiplied by itself) times π.

The Pearson bivariate correlation was used to analyze the intraoperative osteotomy size and the final postoperative ostium size. The independent samples t or Wilcoxon Mann-Whitney test was used to compare the intraoperative osteotomy size and the post operative ostium size between successful and failed cases. Statistical analysis was performed using Microsoft Excel 2003 (Microsoft Corp, Redmond, Washington) and SPSS version 13.0 (SPSS Inc, Chicago, Illinois) computer software.

Fifty patients (mean [SD] age, 63 [15] years), 40 of whom were women, underwent 55 external DCRs (5 patients underwent bilateral surgery). The surgery was distributed evenly between the right and the left sides. The mean follow-up time was 7.1 months (range, 3-12 months). Success was achieved in 49 of 55 cases (89%). The mean (SD) intraoperative osteotomy size was 262.5 (87.5) mm² (range, 104-494 mm²) in all cases, and there was no difference between failed and successful outcomes (250 mm² vs 264 mm²; P = .64, independent samples t test).

Postoperative nasal endoscopy and FEDT were performed in 27 cases (49% of all cases). Other patients either did not return for follow-up or refused to undergo endonasal endoscopy after surgery. It was possible to measure the intranasal ostia in only 24 cases (86%) because 2 patients had a nasal septum deviation that did not allow visualization of their ostia (positive FEDT results in both), 1 patient had a pyogenic granuloma (positive FEDT result), and 1 patient had a scar at the fistula site (negative FEDT result).

Success was achieved in 25 of the 27 patients (93%) who underwent postoperative nasal endoscopy. One patient had a scarred ostium (negative FEDT result) and was scheduled for reoperation. The other patient had a pyogenic granuloma at the ostium site and late dye appearance (>5 minutes) on his FEDT; therefore, his case, too, was considered a failure. There was no difference in the preoperative osteotomy size and the final ostium size between failed and successful cases (232 mm² vs 251 mm² and 8.8 mm² vs 9.7 mm², respectively; P₁ = 0.6 and P₂ = 0.8, respectively, Wilcoxon Mann-Whitney test).

The intraoperative osteotomy size was 256.3 (89.0) mm² (range, 104-441 mm²) among patients who underwent postoperative nasal endoscopy (Figure 4). The ostium size was 9.6 (6.7) mm² (range, 1.26-30.5 mm²). The intraoperative osteotomy size was positively correlated with the postoperative intranasal ostium size (r  = 0.45; P = .03, Pearson bivariate correlation) (Figure 5). The quadratic fit method showed better correlation than the linear fit method (R² quadratic, 0.46; R² linear, 0.20).

Postoperative complications included pyogenic granuloma at the ostium size, with a positive delayed FEDT result (>5 minutes) in 1 patient (Figure 6). Two other patients had scars at the ostia and are scheduled for reoperation. No intraoperative complications were encountered in this group of patients.

Measurements performed by endonasal endoscopy 3 months after surgery demonstrated that creating a larger osteotomy during an external DCR procedure results in a larger final intranasal ostium. The overall success rate of the DCRs in this series was high (93%), and neither intraoperative osteotomy nor final ostium size influenced the success or the failure of those procedures. There is a trend toward greater success with larger osteotomies; however, failed cases in this series were not associated with smaller-sized intraoperative osteotomies.

The findings of our study are not in agreement with the first report by Linberg et al,² who found that the average diameter of the bony opening created at surgery was 11.84 mm (ours was 18.2 mm), while the average diameter of the healed intranasal ostium was only 1.80 mm (ours was 3.5 mm). Interestingly, they found no correlation between the size of the bony opening and the final size of the intranasal ostium and therefore concluded that larger intraoperative osteotomies do not necessarily result in larger ostia after surgery. They also noted that a good surgical outcome was obtained even with a small ostium. It is possible that they measured the common canalicular opening rather than the true postoperative intranasal ostium or fistula.⁴ Assuming that a round osteotomy was created during surgery, the calculated area of the circle would be 100 mm², with a final ostium size of 2.5 mm². Although these sizes are somewhat smaller compared with our data, Linberg et al² also noted a more than 95% shrinkage of the intranasal ostia.

Other studies have evaluated postoperative nasal ostium size using endonasal endoscopy.^5- 7 Deka et al⁵ found that the intraoperative use of mitomycin C may enhance ostium size by preventing postoperative scarring at the surgery site. Patients treated with higher concentrations of mitomycin C (0.4 mg/mL) had substantially larger ostia (17 mm²) than patients treated without mitomycin C (3.5-4.5 mm²). You and Fang⁷ showed that the intraoperative use of mitomycin C (0.2 or 0.5 mg/mL) was effective in creating larger ostia (20-22 mm²) compared with standard DCR without mitomycin C (13 mm²) and that it was also associated with a higher success rate. Although intraoperative osteotomy measurements were not taken in both studies,^5,7 they indirectly support the claim that most of the opening created during surgery is significantly narrowed by scar tissue over time. The data acquired in our study show that more than 90% of the opening is narrowed either by scar tissue or by fistula (ostium) formation but that even a narrow patent opening suffices for tear drainage and successful surgical outcome. A study by Gonzalvo Ibanez et al⁶ found that the ostium shrank to a lesser (7%) extent when mitomycin C was used compared with standard surgery without mitomycin C (35%) and that the intraoperative use of mitomycin C resulted in a better outcome.

The critical osteotomy size that ensures surgical success has yet to be determined; however, it is largely accepted among oculoplastic surgeons that larger openings result in better outcomes. A recent article by Argin et al⁸ reported that creating a 2 × 2-cm bony opening during surgery might result in ostia that are 1.21 to 4 cm² in surface area as measured by computed tomography 2 years after surgery. Although their final ostium size is similar to ours, comparison of these findings is difficult owing to different measuring techniques used in the 2 studies. Their conclusions that a 2 × 2-cm² bone defect might prevent restenosis and that it ensures success is supported only in part, since no control groups were used to evaluate different-sized openings after surgery.

Mann and Wormald⁹ evaluated postoperative ostia at different time intervals after endoscopic endonasal DCR. They found that the DCR ostium shrinks by a small but significant amount 4 weeks after surgery and then remains relatively stable thereafter. The average ostium measured 11.8 × 7.2 mm (= 84 mm²) at the time of surgery, 10.1 × 6.4 mm (= 64 mm²) at 4 weeks, 9.8 × 6.5 mm (= 63.7 mm²) at 6 months, and 10.1 × 6.6 mm (= 66 mm²) at 12 months. We had a much greater discrepancy between the average intraoperative osteotomy (256 mm²) and the final ostium size (9.6 mm²); however, Mann and Wormald⁹ performed DCR endonasally, and their preoperative measurements were limited to the size of the ostium and did not include the bony osteotomy. They used a 4-mm olive-tipped suction, rather than computer software, to measure the vertical diameter and the horizontal diameter of the ostium; this difference could account for the variations in the measurements between their study and ours. It may be reasonable to assume that the narrowing of an intranasal opening would occur to a lesser extent in endoscopic endonasal DCRs compared with external DCRs.

Additional factors that may contribute to a larger ostium include creation of posterior and anterior flaps rather than a single anterior flap,⁵ appropriate location of the ostium relative to the nasolacrimal sac, extension of ethmoid air cells medial to the sac, and coexistence of intranasal disease.¹ Understanding the endonasal anatomy in relation to the lacrimal fossa is of utmost importance in DCR procedures, and even more so when the endoscopic approach is used.¹⁰

We acknowledge the fact that it would have been more accurate to measure intraoperative ostia, rather than osteotomies, using nasal endoscopy at the end of surgery; however, measurement of the fistula size was not performed. Measurement of the true ostia would demonstrate whether true shrinkage occurs during the healing period.

In conclusion, our findings support the hypothesis that creating larger bony osteotomies during external DCR results in substantially larger ostia as measured by postoperative endonasal endoscopy. It would be reasonable to expect that larger osteotomies would be associated with a higher success rate, but this was not borne out by our results, maybe because of the relatively small sample size. Surgical outcome is apparently influenced by additional yet undetermined factors.