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.

In 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.

In 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.

The preliminary results of this work were presented at the 2022 American Academy of Otolaryngology - Head and Neck Society Foundation Annual Meeting as a poster.

This research did not receive any specific funding from funding agencies in the public, commercial, or not-for-profit sectors.

The authors declare no conflicts of interest.