Anatomic patency is the most common measure of success of DCR. However, anatomic success does not always translate to functional success. Hence, we analysed full success, partial success and anatomic patency separately.6,17
Summary of key findings
Our findings have shown that there was no significant difference between primary endonasal DCR and primary external DCR in terms of full success, partial success and anatomic patency. Subgroup analysis showed no significant difference between prospective and retrospective studies as well as between laser endonasal DCR versus external DCR and non-laser endonasal DCR versus external DCR in terms of efficacy. Mean operative time was found to be significantly shorter in endonasal DCR than in external DCR. The occurrence of postoperative bleeding was not significantly different between the two procedures. Postoperative cutaneous scarring was unique to the external DCR procedure.
The patients from all the trials were derived from eight countries (Australia, Canada, Finland, Iran, Nepal, Turkey, UK and USA). Majority of the studies were concentrated in countries with Caucasian populations, hence providing a limited analysis of other races. This poses as a potential limitation due to the different scarring and healing outcomes of various races.
The lasers used in the studies that had laser endonasal DCR were endocanalicular diode laser,18 holmium:YAG laser,19 KTP laser15 and CO2-Nd:YAG laser,13 whereas the efficacy of other types of lasers was not explored.
One of the major concerns with the use of endonasal DCR for managing NLD obstruction is the lower success rates as compared with external DCR. Our review has shown that both non-laser endonasal DCR and laser endonasal DCR had no significant difference in success rates when compared with external DCR. However, the OR for laser endonasal DCR versus external DCR is higher than that for non-laser endonasal DCR versus external DCR even though both subgroup analyses favour external DCR and are not significant. Maini et al. compared surgical endoscopic endonasal DCR and laser endoscopic endonasal DCR and reported that endonasal laser DCR had better symptomatic success rates at 3 months but lower symptomatic success rates at 12 months. However, this difference is not statistically significant. The authors concluded that the findings suggested that there was a deterioration of results for the endonasal laser group even though the change was not statistically significant.20 There are several ways to carry out non-laser endonasal DCR, which use different materials to expose the lacrimal sac, such as rongeour, drill and chisel, with various advantages and disadvantages.10 Dolman suggested that the use of laser may generate char around the ostium site, requiring postoperative wound cleansing and potentially accounting for the poorer success rates.6
Our studies have a relatively short follow-up period, ranging from 7 to 25 months. Differences in the outcomes for the different DCR procedures may only be apparent in a longer follow-up. It would be interesting to compare results for the various methods of DCR over a longer follow-up period.
Another suggested advantage of endonasal DCR is the shorter operative time. Our review has also shown that endonasal DCR had significantly shorter operative time as compared with external DCR. Moreover, local anaesthesia can be used for endonasal DCR,4 leading to a higher number of cases that can be done in each theatre session,17,21 as well as being able to be done as day cases.4,21 Local anaesthesia expands the population eligible for this procedure, as it allows older and less fit patients21 as well as inpatients for whom hypotensive anaesthesia is not advisable to safely undergo surgery.16 However, it should be noted that local anaesthesia can be used for external DCR as well.16 The use of local anaesthesia may be limited to specific types of procedures and local practices.
Our review found that there was no significant difference between the postoperative bleeding occurrences of both external and endonasal DCR.
We have acknowledged in this review that a cutaneous scar is unique to external DCR. One of the most important advantages of endonasal DCR is the lack of a cutaneous scar and its associated wound complications, such as skin swelling and bruising.6,9,10,17,22 The absence of an external incision diminishes the risk of damage to the medial canthal ligament, orbicularis oculi muscle and pretarsal fibres and therefore maintains the lacrimal pump.10,22,23
Another reported advantage of endonasal DCR is that haemostasis can be easily achieved, leading to less intraoperative bleeding.9,10,16,19 Other advantages of endonasal DCR include direct access to the rhinostomy site,7 the possibility of a thorough inspection of the intranasal anatomy at the time of surgery,7 decreased operative morbidity,10 enhanced recovery and the ability to concurrently address other nasal and/or paranasal sinus abnormalities through the same surgical approach.4,9,10,19
A disadvantage of endonasal DCR is the steep learning curve.4,9,15,23 It also has high equipment and instrumentation costs,23 in particular relating to the use of lasers in endonasal DCR.4 A concern about endonasal DCR is the lack of the sophisticated equipment may result in endonasal DCR not being able to be performed in less developed countries. However, Dolman has shown that by using surgical knives instead of lasers and surgical loupes instead of microscopes or videoendoscopes, both the surgical time and cost can be reduced. He has also performed and taught endonasal DCR in remote clinics in northern Canada and in several developing nations.6 A study reported that endoscopic endonasal DCR generated approximately twice as much income as external DCR and hence was more cost-effective mainly due to the higher number of cases per session, day case operations and using local anaesthesia.21
Ibrahim et al. reported three patients who had a bilateral functionally successful DCR with external DCR done on one side and endonasal endoscopic laser DCR done on the other side. All preferred the laser endonasal DCR procedure, citing a shorter recovery period and lack of skin incision.17 Dolman also reported five patients who underwent both external DCR and endonasal DCR with all preferring the non-laser endonasal DCR route.6
Reported advantages of external DCR include the unimpaired view of surgical area and being able to obtain a lacrimal sac biopsy.9 External DCR has been favoured for patients with lacrimal sac neoplasm,15 evidence of a severe post-traumatic bony deformity of the lacrimal sac15,22 or canalicular pathology.22
Some papers have reported that antimetabolitic agents such as mitomycin C16,19 and 5-FU16 inhibit fibroblast proliferation and hence reduce scarring at the internal ostium, which may be a cause of failure of endonasal DCR. Watts et al. used 5-FU in their endonasal DCR technique with no apparent difference in the results compared with success rates reported in other series. However, they had no control group in their study.16 More studies could be carried out to study the effect of antimetabolitic agents on the outcome of endonasal DCR.
Only three randomized controlled trials were included in this review, and the rest of the prospective trials were non-randomized. Half of the studies included in this review were retrospective ones. Retrospective studies face a problem of having to exclude certain cases due to patient selection bias and inadequate follow-up,22 which may alter the success rates and patients included in the studies and hence affect the comparison of external DCR and endonasal DCR. Ben Simon et al. reports a need for prospective studies, with standardization of blockage site and osteotomy size and strict definitions of improvement and failure in order to evaluate more accurately between the two procedures.9
Another limitation of this review is the heterogeneity in terms of endonasal DCR techniques. The various endonasal DCR methods included in this review used either endoscopic or non-endoscopic means to visualize the surgical site and used different means to ablate nasal mucosa and bone such as powered and mechanical means and laser. Not all the various types of laser endonasal DCR have been reviewed in comparison with external DCR. The use of different lasers in endonasal DCR may lead to varying success rates.8
Furthermore, both external DCR and endonasal DCR are surgical procedures. Hence, the outcomes are often dependent on the surgeons performing the procedures.
We conclude that endonasal DCR has comparable success rates with external DCR, be it using non-laser or laser means. It also has the added advantages of having a shorter operative time and a lack of a cutaneous scar. The steep learning curve and higher costs are drawbacks to the endonasal DCR procedure.