DISCUSSION
Sialendoscopy has enabled the assessment of ductal features and disease status of diverse obstructive sialadenitis and changed the therapeutic modality in salivary duct stenosis to gland-preserving minimally invasive surgery.4,8 In a previous study, we evaluated the prognostic factors related to sialendoscopy in 47 patients with parotid duct stenosis who underwent sialendoscopic dilation as an initial treatment.13 We found that sialendoscopy was clinically satisfactory in relieving the symptoms of patients with parotid duct stenosis. However, stenosis type and grade were significantly associated with the success of the sialendoscopic procedure. For instance, some patients with type 2 stenosis did not respond to the sialendoscopic treatment and received revision surgery. These results prompted us to investigate the therapeutic efficacy of sialendoscopy combined with sialodochoplasty for treatment of type 2 stenoses and to clarify the indications for each surgery in type 2 stenosis.
In this study, we included type 2 stenosis cases that were radiologically diagnosed, and all cases were confirmed as having type 2 stenosis based on sialendoscopic findings during operations. Parotid duct stenoses encompass different types of stenosis in the duct, in which type 2 stenosis features a focal web-like stricture and accompanying megaduct.7 Whereas type 1 inflammatory stenosis may be a precursor form of type 3 fibrotic stenosis, a focal web-like stenosis accompanying megaduct appears to be a distinct type with a different underlying pathogenesis that is not yet fully understood.7 MR sialography is now being considered a preferred technique for the detection of salivary duct stenosis, owing to its non-invasive nature and non-exposure of radiation.18 Sialendoscope-based visualization is also needed because tissue characteristics of the residual duct are important for defining different types of stenosis in addition to the feature of stenotic portion. Furthermore, the radiologically diagnosed stenosis may not always correspond with sialendoscope-based stenosis, as MR sialography cannot exclude false-positive findings, such as physiologic narrowing.
Different treatment strategies have been proposed for various types of stenosis and sialendoscopic dilation has become the first-line treatment for type 2 stenosis. In contrast, types 1 and 3 stenoses allow for conservative care, including sialagogue, gland massage, intraductal saline or steroid instillation, and botulinum toxin injection.10 Salivary duct stenosis can be treated by dilation using the sialendoscope itself by increasing the diameter of the sialendoscope, and also by using various instruments, such as dilators, balloons, and bougies.19 Focally-located, low-grade strictures, and strictures in the distal duct may be the best indications for sialendoscopic dilation. However, diffuse stenoses, high-grade strictures, or inaccessible stenoses in the proximal to mid-duct remain a sialendoscopic challenge.13 An attempt can be made to create an opening using a micro drill with a guide wire in high-grade stenoses in which endoscope fails to enter the proximal lumen over the stricture. However, it often poses a high risk of recurrence and sometimes complications, such as ductal perforation.
Transoral sialodochoplasty can be an additional treatment option if the stricture is located in the distal duct based on preoperative radiologic examinations and if sialendoscopic findings are suggestive of high-grade strictures with a high risk of failure or complication.16,19 In this study, excision of the distal duct, including the stenotic portion, and the creation of a neo-orifice allowed obstructive symptom improvement (complete resolution in 46.2% and partial resolution in 53.8%) in patients, and no recurrence was observed during follow-up. Moreover, widened neo-papilla decreased in size over time and remained well-maintained during follow-up without re-stricture (Fig. 2). We also compared pre- and postoperative changes in the megaduct diameter and excretory salivary flow. Intriguingly, postoperative MR sialography showed that the diameter of megaducts significantly decreased after the transoral sialodochoplasty, and some of the patients (71.4%) returned to almost normal levels. MR sialography showed salivary gland ducts more clearly after the operation, owing to the increases in saliva excretion after stimulation with sialagogues. Although the distal duct beyond the stenotic portion could be visualized after the transoral sialodochoplasty, most patients still showed saliva stasis, probably as the thin walls of the megaducts could not fully recover the naïve contraction ability.
Sialendoscopic dilation is the only feasible technique when the stenotic portion is proximally located and when the dilated duct cannot be pulled to connect with the oral mucosa. Recently, an external combined approach using excision with end-to-end anastomosis or excision with an intervening vein graft has been introduced to treat cases of long segments of type 3 stenosis or when sialendoscopic dilation fails.20 Further studies are needed to investigate the efficacy of combined techniques (transoral or transfacial sialodochoplasty) for gland-preserving management of salivary duct stenosis.21
This study had some limitations. First, due to its nonrandomized retrospective design, the study could not prevent selection bias related to the indications of the procedure. Second, the low number of patients and short follow-up period of this study did not allow for a conclusive analysis regarding the efficacy and recurrence of procedures, although, to date, we have not found any recurrences in our sialodochoplasty cohort. Nevertheless, we have demonstrated that transoral sialodochoplasty is a useful procedure for improving salivary excretory flow and repairing dilated duct, especially in type 2 parotid duct stenosis with a megaduct.
In conclusion, we suggest that type 2 parotid duct stenosis can be successfully treated with sialendoscopy combined with transoral sialodochoplasty, which is recommended for patients with severe degrees of distal stricture accompanying a large megaduct and consequently decreased excretory salivary outflow. Further long-term, randomized studies are required to compare the benefits and drawbacks of sialendoscopy versus sialodochoplasty for the treatment of various types of stenosis.