## 4 Discussion  
Our results confirm the safety and effectiveness of interventional sialendoscopy (both as a single-modality treatment and also when performed as a multimodal approach integrated with repeated DSIs) in a large series of adult patients with RIOS in a short-, medium-, and long-term analysis. Tolerability of interventional sialendoscopy under local anaesthesia was good, as attested by the mean VAS pain (3.1 \(\pm\) 2.3) and the non-occurrence of any complications in the whole population. In addition, the surgeons were able to complete the procedure in all cases. Despite it being largely accepted that the morbidity of interventional sialendoscopy is low, some untoward events may occur, including major events such as avulsion of the duct (2%) or, more frequently, minor complications (23%) such as minor ductal lesions, papillary stenoses, or failure to proceed due to ductal stenoses or masseteric blend [17]. In addition, it is known that a progressive learning curve is required both to optimise clinical effectiveness and to reduce the operative time [18]. In fact, it has been reported that some technical difficulties may be encountered in up to 25% of cases when the procedure is performed by non-highly experienced personnel, i.e., those surgeons who have performed no more than 100 sialendoscopic procedures [18]. On the contrary, the occurrence rate of procedural impediments and the mean operative time progressively decrease as the number of patients treated increases. Under these conditions, it is not surprising that, in the present case series, we did not experience any failure, as we have long-term experience with this operation (more than 860 procedures performed by our senior surgeon P.C. in the last 10 years) in our highly specialised second-level facility for the management of patients with obstructive salivary disease (an average of 300 patients treated every year). Our results document a certain effect of interventional sialendoscopy alone in patients with RIOSs as a whole, as documented by a transient decrease in the number of residual gland swelling episodes in the short term (T4) compared to the baseline, but with a tendency toward worsening over time. On the contrary, a combined therapeutic protocol (interventional sialendoscopy plus adjuvant DSIs) was found to be superior to interventional sialendoscopy alone in the management of adult patients with RIOS, as attested by a significant difference in the mean number of residual salivary swelling episodes between groups at any time, with a long-lasting positive effect still detectable 12 months after the end of the treatments. These results are particularly remarkable if we consider that our case series included a large portion of patients with complicated disease, as about 34% of the patients treated suffered from repeated inflammation due to systemic autoimmune disease or post-actinic/radioiodine treatment, and that a sialendoscopic pattern suggestive of severe inflammatory and scarring anatomic ductal subversion was detected in most patients, including the presence of multiple intraoperative pathological findings in about 35% of cases. The documented effectiveness of (interventional) sialendoscopy with DSIs in patients with RIOS has been previously attested [7; 9; 13; 19] in limited case series of patients. In fact, we have reported that (interventional) sialendoscopy with DSIs significantly reduced the number of painful episodes of sialandenitis and subjective symptoms related to oral discomfort in 22 patients with [PERSON]'s syndrome [13]. In addition, we have also found that the addition of DSIs increased the therapeutic value of (interventional) sialendoscopy in the medium term (i.e., 6 months after the end of the procedure) in 44 adult patientswith recurrent sine causa sialadenitis, even though the two procedures were comparable in terms of effectiveness immediately after the end of treatment [7].