Sialendoscopy is a minimally invasive procedure used to diagnose and treat obstructive salivary gland diseases. Previous studies in the topic have shown mixed results. The present study aimed to evaluate the efficacy and safety of sialendoscopy through previous systematic reviews for different outcomes of several diseases. We also aimed to assess studies’ methodological quality and heterogeneity.
MethodsWe conducted a comprehensive systematic literature search of Pubmed, Embase, Lilacs and Cochrane Library. We included systematic reviews and meta-analyses that used sialendoscopy to treat both lithiasic and alithiasic salivary glands diseases. Data extraction included studies’ characteristics and results. We assessed studies’ methodological quality using the AMSTAR-2 (A MeaSurement Tool to Assess systematic Reviews 2) tool.
Results13 studies were included in the review, being 9 in adult populations and 4 in pediatric populations. Sialendoscopy proved to be effective at the treatment of different lithiasic and other obstructive diseases, but with important heterogeneity. The technique was also considered highly safe in most studies. However, studies had a critically low quality of evidence.
ConclusionsMost studies demonstrated high efficacy and safety of sialendoscopy, but with critically low quality of evidence. We still lack randomized studies in this field, and future systematic reviews on the topic should follow current guidelines to improve conduction and reporting.
Salivary gland obstruction affects approximately 1% of the general population. Common symptoms include pain and edema that worsen when eating. Sialolithiasis is responsible for 60%–70%1 of all salivary gland obstructions. When the stone is large enough to obstruct the salivary duct, there is accumulation of saliva, with eventual chronic inflammatory response. Persistence of the obstruction is a risk factor for retrograde infections because of stagnation of saliva.
Sialendoscopy can be used to manage both lithiasic and alithiasic diseases of salivary glands, also known as Obstructive Salivary Gland Diseases (OSGDs), and for diagnosis, treatment, and assistance in surgery. Until recently, treatment of sialadenitis in symptomatic cases consisted of gland excision, with an inherent risk for adverse events.2 Asymptomatic or oligosymptomatic cases usually have conservative management, with satisfactory preservation of gland function, but with risk of salivary duct distension and persistence of symptoms due to saliva stagnation.
In the last few decades, minimally invasive techniques have been developed to treat symptomatic lithiasic and alithiasic salivary gland obstructions. Sialendoscopy uses small semi-rigid or semi-flexible endoscopes to access salivary ducts orally and visualize its’ lumen. It was introduced as an alternative to surgical removal of salivary glands, reducing morbidity related to the procedure and preserving the salivary glands. Many studies have shown sialendoscopy as a viable option for removal of stones in salivary ducts. It can also be used in children to treat juvenile recurrent parotitis, although smaller salivary ducts in children are a complicating factor. For instance, sialendoscopy has been used as the preferred method to treat both lithiasic and alithiasic OSGDs in many countries.
There are several systematic reviews and meta-analyses assessing sialendoscopy in different lithiasic and alithiasic OSGDs in adults, adolescents, and children. Most of them have shown high efficacy and safety of the procedure. However, most studies evaluate different diseases of the salivary glands, applied to varied populations. There is no single study evaluating different outcomes in all OSDGs. Moreover, there is also unknown what is the overall quality of evidence of these published reviews. In the same way, there is high clinical heterogeneity between the different published studies what can cause confusion in the interpretation of these results.
The present study evaluated the efficacy of sialendoscopy to treat different OSGDs, lithiasic or alithiasic, analyzing all published systematic reviews and meta-analyses in the field. We also assessed all studies` results and evaluated methodological quality.
MethodsEligibility criteria and data extractionWe made a systematic search using the terms (“sialendoscopy” OR “sialoendoscopy”) in the Medline database in PubMed, Embase, Lilacs and Cochrane Library. Systematic reviews and meta-analyses of clinical trials or observational studies of any language and date up to April 2022 were eligible for inclusion. We included studies with both lithiasic and alithiasic OSGDs. After the search, assessment for eligibility and data extraction were made by one reviewer (L.L.M.). Data extraction included cited studies, search strategy, language, period of search, databases searched, PICO strategy (Population, Intervention, Control and Outcome),3 use of the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guideline,4 reporting of publication bias, primary outcomes, type of statistical analysis, heterogeneity, and reporting of methodological quality.
Study characteristics were described by their search strategy, language, period of search, databases searched, other search strategies, use of PRISMA, reporting of publication bias, number of included articles, population, intervention, outcome, reporting of quality of evidence, main results, and reporting of heterogeneity. These characteristics were summarized in Tables.
Methodological quality was assessed using the AMSTAR-2 tool.5 AMSTAR-2 is a critical appraisal tool for systematic reviews that include both randomized and non-randomized studies. It is used to assess quality of evidence taking into account critical domains in construction and reporting of systematic reviews and based on that, rates the confidence in the results of the review as low, medium or high. The tool was used by two independent investigators (L.K.S. and M.F.D.). Lack of consensus in any item was resolved by a third author (L.L.M.).
AMSTAR-2 tool defines several critical domains that should be accounted for when evaluating study quality. These are: prior establishment of review methods through protocol (Item 2), use of a comprehensive literature search strategy (Item 4), list of exclusions with justifications for exclusions (Item 7), assessment of risk of bias (Item 9), use of appropriate method in meta-analyses (Item 11), interpretation and discussion of the impact of risk of bias in the results (Item 13), and assessment of publication bias (Item 15).
Other items are considered non-critical by the authors but are also important to be assessed for. According to AMSTAR-2 authors, studies with one critical flaw are considered of low quality. Studies with more than one critical flaw are considered of critically low quality. In case there are no critical flaws, studies have moderate quality if they have more than one non-critical flaw and have high quality if they have one or no non-critical flaw.
We also summarized studies’ results separately for studies that included only lithiasic or alithiasic OSGDs, as well as studies that included both lithiasic and alithiasic OSGDs in their analyses. PRISMA reporting guideline was used in manuscript preparation.
ResultsStudy selectionWith the presented search strategy, we identified a total of 1,260 studies. Of those, 28 were identified to be systematic reviews or meta-analyses. After exclusion of 12 duplicate studies, 16 studies were assessed by full text. Three articles were excluded because sialendoscopy was not the intervention of interest and 13 studies1,2,6–16 were included in the final analysis. A flowchart of the inclusion of studies is presented in Fig. 1.
Study characteristicsMost of the assessed systematic reviews and meta-analyses included only observational studies,1,2,6–11,13,15,16 with most of them being retrospective studies. All of them reported their search strategy and all but one,9 reported search period. Most of them searched through a variety of databases, except for two,12–15 which included only pubmed. Seven studies described the use of PRISMA guideline for reporting results.6,8,10,12–14,16
The population evaluated in different studies significantly varied. Of the nine studies in adult populations, four studies included only lithiasic OSGDs,1,7,13,15 one study included OSGD with underlying Sjogren syndrome,14 one study included radioiodine induced sialadenitis10 and three studies included both lithiasic and alithiasic OSGDs.6,9,16 Of the 4 studies in children and adolescents, two included only lithiasic OSGDs9,11 and two included juvenile recurrent parotitis.8,12 All of them included use of sialendoscopy as an intervention, although some included associated interventions, such as corticosteroid use,14,16 saline solution,14 and other medication treatments.12 In two studies, the intervention was surgery combined to sialendoscopy assistance.1,7 The studies assessed different outcomes: sialendoscopy effectiveness,1,2,6,9,11,16 symptoms resolution,7,8,10,13–16 safety and adverse events1,6,11 recurrence of the disease or symptoms,12 and salivary gland preservation.13
Study PICO strategy is shown in Table 1. We did not report control analyses because most primary studies had no comparator. As a result, when studies evaluated efficacy, they reported success rate of sialendoscopy, recurrence rate, or symptom resolution. When evaluating safety, studies reported minor and major complications. Study characteristics are shown in Table 2. We also evaluated what primary studies were cited in each systematic review and meta-analysis using a citation matrix (Table S1; Supplementary Material). As noted, there was a large variability in the primary studies included in the reviews, although pediatric studies were more likely to include the same primary studies in their reviews.
PICO strategy used in included studies.
Study | Population | Intervention | Outcome |
---|---|---|---|
Lithiasic obstructive sialadenitis | |||
*Studies with adult population | |||
Jadu, 2014 | Adults with obstructive sialadenitis (lithiasic) | Sialendoscopy-assisted stone removal surgery | Symptom resolution and residual sialolithiasis |
Roland, 2017 | Adults with obstructive sialadenitis (lithiasic) | Sialendoscopy-assisted parotid stone removal surgery | Efficacy and safety of sialendoscopy-assisted parotid stone surgical removal |
Chiesa-Estomba, 2020 | Adults with obstructive sialadenitis (lithiasic) | Sialendoscopy associated with laser-assisted lithotripsy | Symptom resolution and glandular preservation rate |
Galdermans, 2020 | Patients with parotid sialolithiasis | Sialendoscopy or sialolithotripsy alone and a combination of both techniques | Partial or complete symptom improvement |
*Studies with pediatric population | |||
Silva, 2016 | Children and teenagers with obstructive sialadenitis (lithiasic and alithiasic) | Sialendoscopy | Effectiveness of sialendoscopy |
Schwarz, 2017 | Children and teenagers with obstructive sialadenitis (lithiasic and alithiasic) | Sialendoscopy | Efficacy and side effects |
Lithiasic or alithiasic obstructive sialadenitis | |||
*Studies with adult population | |||
Strychowsky, 2012 | Adults with obstructive sialadenitis (lithiasic and alithiasic) | Sialendoscopy | Efficacy and safety of sialendoscopy |
Atienza, 2015 | Adults with obstructive sialadenitis (lithiasic and alithiasic) | Sialendoscopy | Obstruction resolution (sialendoscopy alone or combinated) |
Donaldson, 2021 | Adults with obstructive sialadenitis (lithiasic and alithiasic) | Sialendoscopy associated with oral corticosteroids | Partial or complete symptom improvement or lithiasis resolution |
Alithiasic obstructive sialadenitis | |||
*Studies with adult population | |||
Cung, 2017 | Adults with radioactive iodine-induced sialoadenitis refractory to medical treatment | Sialendoscopy | Clinical improvement (symptom reduction) |
Coca, 2020 | Symptomatic sialoadenitis due to Sjogren's syndrome | Corticoid or saline solution associated sialendoscopy | Partial or complete symptom improvement |
*Studies with pediatric population | |||
Ramakrishna, 2014 | Children and teenagers with juvenile recurrent parotitis | Sialendoscopy | Symptom resolution |
Garavello, 2018 | Children and teenagers with juvenile recurrent parotitis | Sialendoscopy and other drug treatments | Sialadenitis recurrence rate |
Methodological characteristics of included studies.
Study | Language | Period | Databases | Other search methods | Included articles | Study designs reported | PRISMA use |
---|---|---|---|---|---|---|---|
Lithiasic obstructive sialadenitis | |||||||
*Studies with adult populations | |||||||
Jadu, 2014 | English | 2004 to 2013 | MEDLINE, EMBASE, and Cochrane Library | References of included studies | 11 | Not reported | No |
Roland, 2017 | English | Up to March 2015 | PubMed, Embase, Cumulative Index to Nursing, Allied Health Literature and the Cochrane Database of Systematic Reviews | Search for non-published data | 10 | Primarily retrospective (not specified how many prospective or retrospective) | No |
Chiesa-Estomba, 2020 | English, German, French and Spanish | Up to 2020 | PubMed, Google Scholar, and Scopus | ? | 16 | 11 retrospective and 5 prospective (non-randomized) | Yes |
Galdermans, 2020 | January 2007 to January 2017 | Pubmed | ? | 13 | 10 case series (7 retrospective and 3 prospective), 1 case-control, 1 observational and 1 evaluation study | ? | |
*Studies with pediatric populations | |||||||
Silva, 2016 | English, Italian, Portuguese and Spanish | ? | Pubmed, Scielo, and Cochrane | ? | 7 | 7 case series reports | ? |
Schwarz, 2017 | English, Italian, French and Spanish | January 1990 to January 2017 | Africa-Wide Information, Biosis (Previews 1969–2016), Cochrane, Embase (from 1947), LILACs, Medline (from 1946), PubMed, and Web of science | References of included studies | 17 | 17 case series (15 retrospective and 2 prospective) | No |
Lithiasic or alithiasic obstructive sialadenitis | |||||||
*Studies with adult populations | |||||||
Strychowsky, 2012 | English | Up to October 2010 | MEDLINE, EMBASE, and Cochrane Library | References of included studies | 29 | Not reported | Yes |
Atienza, 2015 | English, French, Italian, Portuguese and Spanish | Up to April 2014 | MEDLINE, EMBASE, ISI Web of Knowledge, The Cochrane Library, and the NHS Centre for Reviews and Dissemination | References of included studies | 49 | Not reported | ? |
Donaldson, 2021 | English | Up to September 2020 | PUBMED, EMBASE, PROQUEST, and Cochrane Library | ? | 9 | 8 case series and 1 prospective comparative study | Yes |
Alithiasic obstructive sialadenitis | |||||||
*Studies with adult populations | |||||||
Cung, 2017 | English | Up to April 2017 | MEDLINE, EMBASE, and Cochrane Library | ? | 8 | 6 retrospective and 2 prospective studies | Yes |
Coca, 2020 | English | Up to August 2020 | PubMed, Cochrane, and Scopus | ? | 6 | 2 RCTs and 4 case series | Yes |
*Studies with pediatric populations | |||||||
Ramakrishna, 2014 | English | Up to November 2013 | MEDLINE, EMBASE, Cochrane Library, and Google Scholar | References of included studies | 7 | 4 cohort studies and 3 studies with no comparator | Yes |
Garavello, 2018 | English | January 1990 to April 2018 | Pubmed | References of included studies | 19 | 1 RCT, 2 studies with comparator, 20 retrospective case series and 1 case report | Yes |
In general, the sialendoscopy method was referred to as effective and well tolerated. Individual study results are presented in Table 3. In studies evaluating exclusively adults with only lithiasic OSGDs, success rate in stone removal was highest in Roland (2017),1 and all other reviews identified high success rate, although Jadu (2014)7 included studies with moderate heterogeneity of success rates. Symptom improvement and resolution was high, with a low rate of complications. In children and adolescents, although studies had a very low quality of evidence, sialendoscopy was effective with high improvement of symptoms.
Main results of included studies and heterogeneity.
Article | Main results | Heterogeneity | Assessment of quality of evidence |
---|---|---|---|
Lithiasic obstructive sialadenitis | |||
*Studies with adult populations | |||
Jadu, 2014 | Success rate range: 69%–100% | Moderate | Not evaluated |
Very few complications | |||
Grouped success rate: 92.8% (95% CI 87–96) | |||
Roland, 2017 | Stone removal rate: 99% (95% CI 97–100) | Low (moderate for complications) | Moderate (Gu et al. J Clin Epidemiol 2016; 69:199–207.e192) |
Symptom improvement: 97% (95% CI 93–99) | |||
Gland preservation: 100% (95% CI 99–100) | |||
Complications: 6% (95% CI 1–15) | |||
Chiesa-Estomba, 2020 | (1) Resolution of obstruction: 87.3% (95% CI 71–100) | No meta-analyses | Low (National Institute for Health and Clinical Excellence) |
(2) Gland preservation: 97% | |||
(3) Adverse events <3% | |||
Galdermans, 2020 | (1) Mean success rate 88.7% (range 71.4%–100%) | No meta-analyses | Not evaluated |
(2) Low rate of complications and no major complications | |||
*Studies with pediatric populations | |||
Silva, 2016 | Efficacy range: 83%–93% | No meta-analyses | Not evaluated |
Schwarz, 2017 | Reccurency rate (symptom or stone): 14.5%, most of them in JRP | No meta-analyses | Not evaluated |
Lithiasic or alithiasic obstructive sialadenitis | |||
*Studies with adult populations | |||
Strychowsky, 2012 | (1) Success of sialendoscopy alone: 86% (95% CI 83–89) | High (1)/Low (2) | Not evaluated |
(2) Sucess of sialendoscopy with combined access: 93% (95% CI 89–96) | |||
(3) Success range in radioiodine-induced sialadenitis: 50%–100% | |||
(4) Need of gland ressection range: 0%–11% | |||
Few major complications | |||
Atienza, 2015 | (1) Resolution of obstruction in sialendoscopy alone: 76% (95% CI 71%−82%) | High | Low (SIGN ‒ Scottish Intercollegiate Guidelines Network) |
Resolution of obstruction in open surgery with sialendoscopy: 91% (95% CI 88–94) | |||
(2) Gland preservation rate range in sialendoscopy alone: 75.5%–100% | |||
Gland preservation rate range in open surgery with sialendoscopy: 66.7%–100% | |||
Donaldson, 2021 | Success rate: 89% | No meta-analyses | Low (qualitative; reference not specified) |
Alithiasic obstructive sialadenitis | |||
*Studies with adult populations | |||
Cung, 2017 | Clinical improvement range: 75%–100% | No meta-analyses | Moderate (GRADE) |
Coca, 2020 | (1) No estimation symptom resolution alone | High (1)/Low (2) | High/Moderate (National Institute for Health and Clinical Excellence) |
(2) Symptom resolution or symptom improvement: 95% (95% CI 90–99) | |||
*Studies with pediatric populations | |||
Ramakrishna, 2014 | (1) Grouped success rate (no recurrence of sialadenitis): 73% (95% CI 64–82) | Low | Not evaluated |
Success rate by gland (no recurrence of sialadenitis): 81% (95% CI 75–87) | |||
Grouped rate of patients with no necessity of other sialendoscopy: 87% (95% CI 81–93) | |||
Garavello, 2018 | (1) Recurrece rate: 25.8% (95% CI 21.5–30.8) | Not evaluated | Low (qualitative; reference not specified) |
(2) Success rate: 74.2% (95% CI 69.2–78.5) |
In studies including both lithiasic and alithiasic OSGDs in adults, we identified a large heterogeneity of outcomes, which makes it difficult to interpret their individual results. Although success rates of sialendoscopy alone was lower in Strychowsky (2012)6 and Atienza (2015),2 there was a high success rate when sialendoscopy was used combined with open surgery. Donaldson (2021)16 had a high success rate. All three studies had few adverse events.
In studies analyzing specifically alithiasic OSGDs in adult populations, Cung (2017)10 identified a high clinical improvement in patients with radioiodine-induced sialadenitis, with moderate quality of evidence and heterogeneity (although meta-analysis was not conducted). Coca (2020)14 identified a high clinical improvement in patients with underlying Sjogren’s syndrome. In children and adolescents with juvenile recurrent parotitis, success rate (as defined by absence of recurrence) was moderate in both studies.
Assessment of methodological qualityAssessment of methodological quality using the AMSTAR-25,17,18 tool is shown in Table 4. Since we included studies regarding different populations, we will present the results according to the research question. Although not evaluated through the AMSTAR-2 tool, it is important to note that most systematic reviews and meta-analyses included low quality primary studies, most of them being observational retrospective studies. Few studies included Randomized Controlled Trials (RCTs).
Assessment of methodological quality of studies using the AMSTAR-2 tool.
Lithiasic obstructive sialadenitis | Lithiasic and alithiasic obstructive sialadenitis | Alithiasic obstructive sialadenitis | Number of Yes or Partially Yes | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Adults | Children and adolescents | Adults | Adults | Children and adolescents | ||||||||||
Jadu, 2014 | Roland, 2017 | Chiesa-Estomba, 2020 | Galdermans, 2020 | Silva, 2016 | Schwarz, 2017 | Strychowsky, 2012 | Atienza, 2015 | Donaldson, 2021 | Cung, 2017 | Coca, 2020 | Ramakrishna, 2014 | Garavello, 2018 | ||
1) Research questions and criteria (PICO) | Yes | Yes | Yes | Yes | Yes | Yes | Yes | Yes | Yes | Yes | Yes | Yes | Yes | 13/13 |
2) Prior establishment of review methods | No | No | No | No | Partial yes | No | No | No | No | No | No | No | No | 1/13 |
3) Study design selection explanation | No | Yes | Yes | Yes | Yes (in protocol) | Yes | Yes | No | Yes | Yes | Yes | Yes | No | 10/13 |
4) Comprehensive literature search | Partial yes | Partial yes | Partial yes | No | Partial yes | Partial yes | Partial yes | Partial yes | Partial yes | Partial yes | Partial yes | Partial yes | No | 11/13 |
5) Study selection in duplicate | Yes | Yes | Yes | No | Yes | Yes | Yes | Yes | Yes | No | Yes | Yes | Yes | 11/13 |
6) Data extraction in duplicate | Yes | Yes | Yes | No | Yes | Yes | Yes | Yes | Yes | No | Yes | Yes | Yes | 11/13 |
7) Justification of exclusions | Partial yes | Yes | Yes | Yes | No | Yes | Yes | Partial yes | Partial yes | No | Yes | Yes | Partial yes | 11/13 |
8) Adequate detail describing included studies | No | Yes | Yes | Yes | No | Yes | No | No | Yes | Yes | Yes | Yes | Partial yes | 9/13 |
9) Risk of bias assessment in RCTs and NRCTs | No | Partial yes | Partial yes | No | No | No | No | No | No | Partial yes | Yes | No | No | 4/13 |
10) Sources of funding in include studies | No | No | No | No | No | No | No | No | No | No | No | No | No | 0/13 |
11) Use of appropriate statistical methods in RCTs and NRCTs | Yes | Yes | No meta-analyses | No meta-analyses | No meta-analyses | No meta-analyses | Yes | Yes | No meta-analyses | No meta-analyses | Yes | Yes | No | 6/13 |
12) Risk of bias impact assessment | No | Yes | No meta-analyses | No meta-analyses | No meta-analyses | No meta-analyses | No | No | No meta-analyses | No meta-analyses | Yes | No | No | 2/13 |
13) Risk of bias when interpreting or discussing results | No | Yes | Yes | No | No | No | No | No | Yes | Yes | Yes | No | No | 5/13 |
14) Explanation and discussion of heterogeneity | No | Yes | Yes | No | No | No | Yes | Yes | No | No | Yes | No | No | 5/13 |
15) Adequate investigation of publication bias | Yes | No | No meta-analyses | No meta-analyses | No meta-analyses | No meta-analyses | No | No | No meta-analyses | No meta-analyses | No | Yes | No | 2/13 |
16) Sources of conflict of interest | Yes | Yes | Yes | Yes | Yes (in protocol) | Yes | Yes | Yes | Yes | Yes | Yes | Yes | Yes | 13/13 |
Yes in all domains | 6/16 | 11/16 | 9/16 | 5/16 | 5/16 | 7/16 | 8/16 | 6/16 | 7/16 | 5/16 | 12/16 | 9/16 | 4/16 | |
Yes in critical domains | 2/7 | 3/7 | 2/7 | 1/7 | 0/7 | 1/7 | 2/7 | 1/7 | 1/7 | 1/7 | 4/7 | 3/7 | 0/7 | |
Rating | Critically low | Critically low | Critically low | Critically low | Critically low | Critically low | Critically low | Critically low | Critically low | Critically low | Critically low | Critically low | Critically low |
Overall compliance was 46% (range 25%–75%), and compliance in critical domains was 23% (range 0%–57%). All reviews had critically low quality of evidence. Critical domains with the lowest compliance were previous protocol registration (Item 2) and assessment of publication bias (Item 15). The only domain with no compliance was reporting of funding in individual studies, which is a non-critical domain.
Of four studies in adult populations that included only lithiasic OSGDs, Roland (2017)1 and Chiesa-Estomba (2020)13 had higher methodological quality in adult populations. When regarding lithiasic OSGDs in pediatric populations, Schwarz (2017)11 had a slightly higher methodological quality than Silva (2016).9 In studies that included both lithiasic and alithiasic OSGDs, the three included studies had very similar methodological quality in adults. In studies with only alithiasic OSGDs in adults, Coca (2020)14 had a higher methodological quality, although it included only OSGDs with underlying Sjogren syndrome. Ramakrishna (2014)8 had a higher methodological quality in the investigation of juvenile recurrent parotitis.
DiscussionIn the present study, we assessed the efficacy and safety of sialendoscopy to treat several OSGDs in different populations and also in different clinical scenarios. Our analysis included all systematic reviews and meta-analyses in the topic. Studies’ overall results and methodological quality were assessed. According to the available evidence, sialendoscopy has shown to be an effective and safe technique to treat OSGDs. However, we found that all systematic reviews published in the topic have critically low quality of evidence, when assessed by the AMSTAR-2 checklist. The present study provides evidence-based guidance for clinical practice, considering different populations, several diseases, and outcomes.
There are several evidence-based studies published in the literature considering sialendoscopy in the treatment of OSGDs. These studies include systematic reviews with or without meta-analysis with different populations and different outcomes. These studies, sometimes, evaluate the same outcome, but with different inclusion criteria, making the comparison between them sometimes impossible and also demonstrating divergent results. Moreover, the lack of an objective analysis in terms of the quality of the generated evidence, makes it impossible to safely employ these results into clinical practice.
Most analyzed publications included primarily retrospective studies, resulting in low to moderate quality of evidence. There are important biases to consider when analyzing retrospective studies, such as recall bias in subjective outcomes and lack of randomization and close follow-up of patients. Short follow-up was also an important limitation of the primary studies, hindering our capability of identifying long-term symptoms. Study outcomes were assessed and reported differently, adding more bias and heterogeneity. Symptom improvement may be the most important outcome since it is a clinical outcome, but lack of validated standardized methods for evaluating symptoms makes it harder to define what is a relevant improvement. Thus, bias was largely present in our evaluation, which importantly limits reliability of results in studies of sialendoscopy.
Heterogeneity played an important role in our analyses. Generally, included reviews had moderate heterogeneity in their data. This could be due to small sample sizes, variability in technique and surgical equipment and inconsistent reporting. Most meta-analyses included several case reports and case series. These study designs should not be used in meta-analyses, due to large variability of methodology. This also adds heterogeneity to the studies. There was also large heterogeneity in our review, since most studies included different populations, interventions, and outcomes. Even when included reviews evaluated the same research question, there was important heterogeneity in their results, which we attribute to variable methodological quality. The presence of many sources of heterogeneity limits the interpretability and generalizability of all included reviews.
A point should be made regarding the separation of the analysis between lithiasic and alithiasic OSGDs. As noted, 3 studies included both lithiasic and alithiasic OSGDs in their analyses. We opted to include these studies to guarantee that all available data in OSGDs was covered. Moreover, since there was large overlap of primary studies included in the reviews, we cannot properly evaluate the accuracy of sialendoscopy through a simple division of lithiasic and alithiasic OSGDs. However, this does not impact the quality of evidence of presented in each population, since the critically low methodological quality was present in all studies.
Methodological quality of reviews of studies in sialendoscopy was also an important limitation. All included studies had a critically low methodological quality, according to our assessment using the AMSTAR-2 tool, making this point one of the largest weaknesses in the outcome assessment of sialendoscopy technique. Studies lacked especially critical domains, leading to poor ratings. According to AMSTAR-2, studies should be classified with critically low quality when they have more than one critical flaw. The great majority of studies did not include Items 2 (prior establishment of methods) and 15 (assessment for publication bias), considered to be critical, which already led to most of them having critically low quality. We also noted that PRISMA guideline use played an important role when assessing methodological quality. Studies that used it to report their results had generally higher quality of evidence.
Additionally, we would like to make some comments regarding our assessment of methodological quality. In Item 2, regarding prior establishment of review methods, we considered as a “no” when studies reported use of a protocol, but the protocol could not be found in supplementary material or in online platforms for protocol registration. Following AMSTAR-2 recommendations, studies that verified only one database received a “no” in Item 4, regarding search strategy. In Item 7, when authors did not report reading articles in full text, the review received a “no”. This is a point of caution that should be a warning for all authors that intend to conduct a systematic review, with or without a meta-analysis. The better the authors describe the methodology applied at the study, the better the quality score. We also strongly recommend that authors register their projects into specific platforms, assuring a high-quality publication.
Finally, it is important to note that some studies performed meta-analyses, whereas others do not. Naturally, studies with no meta-analyses have lower ratings since they do not score in some items. Even though this is a limitation, it is important to note that, even in other items that do not include only meta-analyses, studies that made meta-analyses also had less flaws.
More primary and secondary studies should be performed using sialendoscopy, with more rigid methodologies and less predictable bias, to better establish the method as gold-standard for OSGDs treatment.
ConclusionIn this analysis of systematic reviews and meta-analyses, we found sialendoscopy to be efficacious and safe. However, the included studies showed critically low quality of evidence. We still lack randomized studies in this field, and future systematic reviews on the topic should follow current guidelines to improve conduction and reporting.
DisclosuresThe preliminary results of this work were presented at the 2022 American Academy of Otolaryngology - Head and Neck Society Foundation Annual Meeting as a poster.
Financial disclosureThis research did not receive any specific funding from funding agencies in the public, commercial, or not-for-profit sectors.
Conflicts of interestThe authors declare no conflicts of interest.