Underwater endoscopic ear surgery vs. microscopic open approach for repair of semicircular canal fistulae secondary to middle ear cholesteatoma: a systematic review and meta-analysis

Introduction

Labyrinthine fistulae are a complication of cholesteatomas, occurring between 0.2–12.9% worldwide (1-3). Of these, 90% occur in the lateral semicircular canal (2). Rarer locations include the cochlea, oval window and posterior semicircular canals. Fistulae result from chronic bony erosion related to osteolytic enzyme secretion from cholesteatomas. When left untreated, labyrinthine fistulae result in vertigo and sensorineural hearing loss caused by labyrinthitis and rarely meningitis can occur. In cases where purulent labyrinthitis is present, recovery of hearing is unlikely (4-6).

The main goal of surgical treatment is to remove the disease, preserve hearing, and prevent secondary symptoms such as vertigo, purulent labyrinthitis and meningitis. Debate still exists regarding either complete or staged removal (7,8). Furthermore, there is no clear evidence regarding superior repair material such as soft or hard tissues, as well as superior methods such as resurfacing or complete canal occlusion.

A technique known as ‘under water endoscopic ear surgery’ (UWEES) for repair of lateral semicircular fistula was first published in 2014 (9). An open mastoidectomy is first performed, and the matrix removal is left as the last operative step, as in traditional microscopic techniques. In the UWEES technique, the mastoid cavity is then flooded with body temperature isotonic solution and an endoscope with irrigation is submerged. This provides a clear magnified operative field whilst minimising the exposure of the delicate membranous labyrinthine tissues to air during matrix dissection. This method may theoretically reduce electrolyte changes in the perilymph and endolymph. However, there is a potential to worsen the hearing due to disruption of the endolymph. Continuous irrigation with isotonic solution could result in large volume replacement of the endolymph. There is also potential seeding of cholesteatoma throughout the ear with irrigation. Whilst positive results have been shown, this technique is not yet widely used due to factors such as the technical novelty and the associated learning curve (10,11).

The objective of this study is to compare outcomes of underwater endoscopic to traditional open microscopic approaches for repair of labyrinthine fistulae using a systematic review and meta-analysis. We present this article in accordance with the PRISMA reporting checklist (available at https://www.theajo.com/article/view/10.21037/ajo-24-11/rc).

Methods

Study selection

The inclusion and exclusion criteria are as described below for UWEES (Table 1) and microscopic approach (Table 2). No limits were placed on publishing date, time period and study design. Ethics approval was not required due to the study being a systematic review of previously published data.

Study identification

The search was conducted on Medline (on Ovid platform), Embase (on Ovid platform), Cochrane Library (on Ovid platform) and Web of Science (on Web of Science platform) from inception to the present. Unpublished studies were searched on Google scholar, Mednar, and ProQuest Dissertations and Theses Global: Health and Medicine. Databases of ongoing trials were searched including ClinicalTrials.gov (http://clinicaltrials.gov/), Australia and NZ clinical trials (https://www.anzctr.org.au/), NHMRC Clinical Trials (https://www.ctc.usyd.edu.au/), metaRegister of Controlled Trials (http://www.controlled-trials.com/mrct/), the EU Clinical Trials register (https://www.clinicaltrialsregister.eu/) and the World Health Organization (WHO) International Clinical Trials Registry Platform Search Portal (http://apps.who.int/trialsearch/). Conference lists for related abstracts and presentations were searched. Finally, reference lists of relevant studies were searched to find any additional studies. The database searches for Medline and Embase were peer-reviewed by a librarian and any differences resolved by discussion. Search strategies were replicated for Cochrane Library and Web of Science. The databases were last searched on 2nd February 2023 for both UWEES and microscopic groups and all other sources were last searched on 3rd March 2022. A detailed search strategy for each database is available as a supplement (Appendix 1).

Two reviewers (R.C.) and (M.K.) independently screened titles and abstracts against inclusion and exclusion criteria. The full texts of potentially relevant studies were subsequently examined by both authors independently. Where full texts were not available, we contacted the authors for access. Differences were resolved through recourse to senior review autShors (N.J., N.P.P.).

Data extraction and management

Papers selected for retrieval were analysed separately by the primary reviewer (R.C.) and the following data extracted in duplicate onto a Microsoft Excel Worksheet: demographics, disease characteristics, surgical methods, follow up period, and measured outcomes (hearing, disease clearance, vestibular function, and facial nerve function). Where studies grouped BC unchanged and improved into one group, it was taken as all BC unchanged. In studies where only patients with BC improved and worsened hearing outcomes where described, the rest were taken as BC unchanged. Studies were excluded if they were found to be of low quality (i.e., case reports). All results for all measures, time points and analyses were sought. When required, data was estimated from figures and means/standard deviations calculated from tables.

Statistical analysis

The difference in mean bone conduction threshold score was assessed using standardized mean difference (Cohen’s d) effect measure. The difference in vertigo cases and facial nerve weakness between pre- and post-operative periods was assessed using risk difference effect measure. The improvement in bone conduction threshold as a categorical variable and residual or recurrent disease variables were assessed using the respective proportion of event as the effect measure.

Tests of heterogeneity were conducted using Q statistic; which is distributed as a chi-square random variable (assumption of homogeneity of effect sizes). The between-study heterogeneity was assessed with the I² statistic, with interpretation as follows: I²<25% means no heterogeneity, I²<50% means low heterogeneity, I²<75% means moderate heterogeneity, I²≥75% indicates high heterogeneity (12,13).

A meta-analysis of the treatment outcomes (hearing, disease clearance, vestibular function, and facial nerve function) was performed using random effects model specification. The model effects were estimated using restricted maximum likelihood estimation method. The results of the included studies are presented in a forest plot. Meta regression analysis was performed to test the significance of the moderators on the effect size.

P values were two-tailed at a 0.05 level of significance (P values less than 0.05 are considered statistically significant). Meta-analyses were performed in STATA V17.0 software (StataCorp 2021.).

Quality appraisal

The primary reviewer (R.C.) assessed the risk of bias for each included study using the National Institutes of Health (NIH) quality assessment tool for case series studies (14). The quality of evidence was classified into three grades: poor, fair or good quality.

All studies included in the meta-analysis were retrospective case series, thus general flaws of retrospective studies such as the assumption of accurate record keeping apply to the studies which did not undergo formal risk of bias assessment.

Results

A total of 358 UWEES studies were retrieved through searching databases, and one study was identified from searching grey literature. Prior to screening 105 duplicates were removed. The remaining 254 studies underwent title and abstract screening. Studies which used the endoscopic technique without being underwater were excluded (15,16). Case reports were excluded (9). After unrelated studies were removed a total of 4 studies underwent data extraction (Figure 1A).

Figure 1 Flow diagrams of UWEES (A) and microscopic (B) study selection according to the PRISMA guidelines. UWEES, under water endoscopic ear surgery.

In the microscopic group, a total of 734 studies were retrieved through searching databases, and 1 study was identified from searching grey literature. Prior to screening 230 duplicates were removed. The remaining 505 studies underwent title and abstract screening, and 76 studies underwent full text screening. Studies with extensive petrous bone cholesteatoma were excluded (17,18). One study with no hearing outcomes were excluded (19). After unrelated studies were excluded a total of 39 studies underwent data extraction (Figure 1B).

All included studies were retrospective case series. There were no randomised control trials (RCTs) identified.

Of the 4 studies included in meta-analysis for UWEES, 3 studies were judged to be good quality (20-22). One study was considered to be of fair quality (23). Of the 39 studies included in meta-analysis for the microscopic group, 29 studies were judged to be good quality. These included 9 studies published prior to 2010 (2,5,24-30) and the remainder between 2010–2022 (1,31-49). Eight studies were considered to be of fair quality (50-57). Two studies were considered to be of poor quality (58,59). This was based on a detailed breakdown of individual studies (Tables S1,S2). The final results are displayed in a graphical representation (Figure 2A,2B).

Figure 2 Quality appraisal of UWEES (A) and microscopic (B) studies using the NIH risk of bias tool for case series. Yes, criteria met; No, criteria not met; NR, not recorded; UWEES, under water endoscopic ear surgery; NIH, National Institutes of Health.

All UWEES and microscopic study demographics and outcomes are presented in tables and are available as a supplement (see Tables S3-S5). In the UWEES group, there was a total of 4 relevant publications with 51 subjects (20-22). The mean age of the patients included in the studies was 48 years (range, 4–82 years). In 3 studies, 51% of patients underwent primary surgery, the remaining undergoing revision surgery (20,21,23). This data was not available for the final study (22). Irrigation solution used was saline or ringer’s lactate in one study (20), saline with corticosteroids (methylprednisolone) in one study (23), saline with corticosteroids (prednisolone) and antibiotics (cefuroxime) in one study (21) and saline or artificial cerebrospinal fluid in one study (22). All patients underwent removal of the cholesteatoma with the matrix followed by sealing of the bony defect. The average length of follow up was 42 months.

In the microscopic group, there was a total of 39 relevant publications with 1,139 subjects. These included 16 studies published prior to 2010 (2,4,5,24-30,50-53,58,59) and the remaining 23 studies published between 2010–2022 (31-46,48,49,54-57,60). The mean age of the patients included in the studies was 46 years (range, 4–88 years). Of the 18 studies with relevant data, 17% underwent revision surgery (2,4,25,27,31-33,35,38,39,42,45,46,52,55,57,59,60). A total of 834 patients underwent complete removal of cholesteatoma and matrix followed by sealing of the bony defect and 113 patients underwent removal of the cholesteatoma leaving the matrix intact over the 33 studies in which fistula repair technique was reported. The average length of follow up was 29 months.

Bone conduction thresholds were reported as overall mean outcomes in 4 UWEES studies (20-23) and 7 microscopic studies (25,31,37,39,49,52,60), and reported as hearing improvement vs. hearing loss in 3 UWEES studies (20-22) and 21 microscopic studies (2,4,5,24,25,27,29-31,33,34,36,39-41,44-46,51,56,58). Thus, these were analysed separately.

The test for overall pooled effect indicated no statistically significant difference in mean bone conduction threshold between pre- and post-operative periods for either UWEES or microscopic methods (standardized mean difference =−0.05, 95% CI: −0.44 to 0.34, P=0.81 for UWEES method and standardized mean difference =−0.56, 95% CI: −1.23 to 0.11, P=0.10 for microscopic). The forest plots for difference in mean bone conduction threshold score for UWEES and microscopic methods are presented in Figure 3A,3B.

Figure 3 Forest plots of pre- and post-operative differnece in mean bone conduction threshol scores for UWEES (A) and microscopic (B) approaches. UWEES, under water endoscopic ear surgery; SD, standard deviation; CI, confidence interval; REML, restricted maximum likelihood.

The proportion of improved bone conduction threshold with UWEES method was 0.09, 95% CI: 0.02–0.24. The corresponding proportion with microscopic method was 0.16, 95% CI: 0.11–0.24. The forest plots for meta-analysis of proportion of patients with improved bone conduction threshold score for UWEES and microscopic methods are available as a supplement (see Figures S1-S3).

Secondary outcomes were pooled where available.

Of the analysed UWEES studies, all studies reported pre- and post-operative vertigo outcomes, and 3 studies had enough data for meta-analysis (20-22). Of the microscopic studies, 17 could undergo meta-analysis (2,4,5,26,27,29-33,36,38,42,43,46,48,55). There was no statistically significant reduction in the risk of vertigo post-operatively using the UWEES method (risk difference =−0.12, 95% CI: −0.34 to 0.09, P=0.27). However, there was a statistically significant reduction in risk of vertigo post-operatively using the microscopic open method (risk difference =−0.49, 95% CI: −0.58 to −0.40, P<0.001).

However, the I² statistic indicated high between-study heterogeneity, with a value of 80.19%. To investigate the potential influence of outlier studies on the results, a sensitivity analysis using a leave-one-out meta-analysis method was conducted. This analysis identified the study by Sheehy, 1979 as having the highest impact on the pooled effect magnitude and its standard error (4). When we excluded this study from the meta-analysis, the I² value decreased to 60.96%. Despite this reduction in heterogeneity, the effect remained statistically significant with a risk-difference of −0.52 (95% CI: −0.60 to −0.45).

The forest plot for meta-analysis of risk difference of vertigo between pre- and post-operative periods for UWEES and microscopic methods are presented in Figure 4A,4B.

Figure 4 Forest plots of pre- and post-operative difference in vertigo cases for UWEES (A) and microscopic (B) approaches. UWEES, under water endoscopic ear surgery; CI, confidence interval; REML, restricted maximum likelihood.

Facial nerve function was able to be analysed for 3 UWEES studies (20,21,23) and 14 microscopic studies (4,27,31,32,34-36,42-44,46,48,54,59). There was no statistically significant reduction in risk of facial nerve weakness post-operatively with either of the two methods (risk difference =−0.00, 95% CI: −0.17 to 0.17, P=0.99 for UWEES method and risk difference =−0.01, 95% CI: −0.04 to 0.02, P=0.49 for microscopic method). The forest plot for meta-analysis of risk difference in facial nerve weakness between pre- and post-operative periods for microscopic and UWEES methods are available as a supplement (see Figures S1-S3).

Of the 4 UWEES studies, 4 patients from one study had residual or recurrent disease (8%) (21). Of the 20 microscopic studies which reported residual or recurrent disease, the pooled proportion of residual or recurrent diseases patient was 0.03, 95% CI: 0.01–0.07 (5,27,30,32-36,38,39,42-44,46,48,49,51,54-56). The forest plot for meta-analysis of proportion of residual or recurrent disease cases for microscopic method are available as a supplement (see Figures S1-S3).

Table 3 presents the results of the Meta regression evaluating the effect of selected moderators on the effect size for microscopic approach. Factors such as lateral semi-circular canal fistula (vs. superior/posterior canal fistula), primary surgery (vs. revision surgery) and positive fistula sign (vs. negative fistula sign) were associated with increase in the difference in risk of vertigo (per patient increase in risk difference was: β=0.006, 95% CI: 0.002–0.010 for lateral semi-circular canal fistula, β=0.006, 95% CI: 0.001–0.011 for primary surgery and β=0.008, 95% CI: 0.003–0.12 for positive fistula sign). Due to the lack of raw data, the effect of moderators was not able to be evaluated for hearing outcome, facial nerve weakness or residual/recurrent disease.

Discussion

This systematic review shows that UWEES may be a safe and effective alternative to the microscopic approach. Efficacy was measured as stable or improved hearing outcome and low rate of secondary complications. The results showed there was no statistically significant difference in both mean bone conduction thresholds pre- and post-operatively as well as proportion of improved bone conduction threshold post-operatively for both UWEES and microscopic methods. Both techniques begin with a canal-wall up or canal-wall down mastoidectomy, with the UWEES technique then involving a fistula repair under continuous irrigation, while the microscopic approach performs the fistula repair with the cavity exposed to air. The microscopic approach carries a risk of suctioning of the perilymph and accidental damage of the membranous labyrinth which may result in irreversible hearing loss. To reduce this risk, a staged procedure is often used, with the complete fistula matrix removed at the second look operation. In other cases, a thin layer of matrix is left intact over the fistula, however this leaves a potential source for ongoing bony erosion and delayed sensorineural hearing loss (7,8). UWEES may address these complications by creating a fluid filled chamber that mimics perilymph, thereby decreasing direct suctioning of the membranous labyrinth and preventing pneumolabyrinth.

This work found that while the UWEES method had no significant association with risk reduction of vertigo post-operatively, the microscopic approach was associated with a statistically significant risk reduction of vertigo post-operatively. However, significant heterogeneity was observed in this outcome. An additional factor that has been considered to influence vertigo outcomes include the choice of repair material. There are suggestions that the ‘sandwich technique, involving a layer of temporal fascia, followed by bone pate, and another layer of temporal fascia, is associated with a lower occurrence of post-operative vertigo (33). It has also been proposed that mastoid obliteration could serve as a barrier for external ear canal induced pressure changes, which have been implicated in the onset of vestibular symptoms following removal of the fistula matrix (39).

Meta-regression was conducted for the microscopic approach showing that individually, the presence of semicircular canal fistula, and primary surgery had a significant relationship with risk difference of vertigo pre- and post-operatively. Revision surgery has been associated with high rates of complications when using the microscopic approach, and may reflect the higher rate of vertigo in some microscopic studies with more patients undergoing revision surgery (38,61). Interestingly, there was no significant relationship of size of fistula (Dornhoffer grade I, II, or III) and risk difference of vertigo pre- and post-operatively in this study (62). It has previously been shown that fistula size has a significant relationship to post-operative hearing outcome (44), however there is no consensus over the preferred surgical method for patients with large fistulae. Some surgeons suggest that the cholesteatoma matrix should be left undisturbed over a large size fistula, with others arguing that there should be complete removal of the matrix regardless of the size (36,42,55,60,63). In the future, it would be useful to conduct meta-regression analysis on an expanded pool of UWEES patients to evaluate if similar factors influence post-operative vertigo.

The rate of recidivism post operatively for the UWEES group was also comparable with microscopic in this systematic review, and both had very low rates of facial nerve weakness secondary to repair. However, the follow up period was relatively short in both groups, with an average length of follow up of 42 months in the UWEES and 29 months in the microscopic group. The existing literature suggests that recurrence rate is significantly higher in patients with more than 10 years of follow up (64). Canal-wall down mastoidectomy has also been associated with a lower rate of both residual and recurrent disease, presumably due to the more extensive visualisation from removal of the posterior canal wall (65). The advantage of the UWEES technique is that the endoscope provides a wide viewing angle, allowing better visualisation of the typically obscured recesses of the middle ear cavity, which may be useful in detecting residual disease.

Underwater endoscopic ear surgery is a relatively new technique in the management of lateral semicircular canal fistulae. However, given its novelty, several limitations arise in performing a systematic review, the first being inadequate follow up time in some patients. This is to be expected given the limited existing data pool, and should aim to be improved in future studies as the data pool increases. One study with <5 patients was included in the review (23). Again, due to the small data pool, this was accepted in this systematic review, however this may contribute to an increased risk of bias.

The lack of raw data overall meant that several clinical/demographic characteristics and outcomes were not fully reported in all studies. The most significantly affected variables were primary vs. revision surgery, side of surgery (left vs. right), and Dornhoffer grade (I, IIa, IIb and III), and the most significantly affected outcomes were facial nerve weakness and residual/recurrent disease. Because of this, the effect of moderators was only able to be evaluated for incidence of vertigo. There is potential confounding of the other outcomes which are underestimated in this systematic review. The meta-regression analysis also faces potential risks of overfitting given its small sample size of 4 studies per moderator, as well as ecological fallacy risk that may occur when drawing conclusions on effect size from aggregate level characteristics. Therefore, findings from this meta-regression analysis should be interpreted with caution, particularly when considering its applicability to larger populations. It is possible that the fistula repair technique (complete matrix removal and fistula sealed vs matrix left intact over the fistula) had a significant impact on the hearing outcomes, and matrix management has been a source of ongoing debate in the existing literature with no consensus (1,3,4,6,7,66,67). There is also a small potential that the type of irrigation solution used, i.e., saline vs. ringer’s lactate vs. artificial cerebrospinal fluid has an impact on the hearing outcomes, however this would again require a larger sample size and fully reported raw data. The level of evidence of the reviewed literature comprising level 4 studies (case series) reduces the strength of the outcome variables. There was overall a low-moderate risk of bias in both the UWEES and microscopic groups, with the majority of studies being of good quality. Studies occasionally did not report the study design characteristics and demographics of participants (37,50-52,54,58). Follow up time was also inadequate in 2/4 studies in the UWEES group (22,23). Although primary hearing outcome was defined clearly in majority of studies, monitoring of residual/recurrent disease was less clear. This may have been subjective according to symptoms, without using objective measurements such as repeat imaging or relook surgery. This reflects the current lack of guidelines in the follow up of labyrinthine fistulae post-operatively.

The limitations of the systematic review itself includes a small number of studies in the UWEES group due to the novelty of the technique. Future research will add to the existing pool of data. Differences in reporting (mean hearing outcome vs. categorical hearing outcome) meant that not all studies could undergo meta-analysis. Further research should focus on increasing follow up duration to better assess long term outcomes, and compare UWEES and microscopic methods in a single study to reduce potential confounding factors.

Conclusions

UWEES is a novel technique which has been used with at least short-term success in the repair of labyrinthine fistulae secondary to cholesteatomas. This systematic review supports the existing literature with comparable hearing outcome and rate of recidivism between UWEES and microscopic methods. There was a reduction in post operative vertigo in the microscopic group not demonstrated in the UWEES, however with high heterogeneity. Further research comparing both UWEES and microscopic methods in a single study with extended follow up is required.

Acknowledgments

Thank you to Jackie Edwards for her contribution to the database search.

Funding: None.

Footnote

Reporting Checklist: The authors have completed the PRISMA reporting checklist. Available at https://www.theajo.com/article/view/10.21037/ajo-24-11/rc

Peer Review File: Available at https://www.theajo.com/article/view/10.21037/ajo-24-11/prf

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://www.theajo.com/article/view/10.21037/ajo-24-11/coif). A.S. serves as an unpaid editorial board member of Australian Journal of Otolaryngology from January 2019 to December 2024. The other 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. Ethics approval was not required due to the study being a systematic review of previously published data.

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/.

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