Early Clinical Mapping of Submandibular Gland Fistula: A Case Report and Systematic Review

Introduction  Submandibular gland fistula (SGF) is a rare subset of salivary gland fistulas. It is seldom tough to diagnose them prior to surgical exploration, and it is often clinically confused with close differentials. An early diagnosis based on pertinent clinical features and focused radiological findings can be pivotal in optimal management and help prevent recurrence and avoid unnecessary investigations/interventions. Objective  To review articles that discuss SGF and provide vital etiological, clinical, and imaging features of this rare entity that can aid in early clinical diagnosis. Data Synthesis  An extensive review involving PubMed and Google Scholar and reported in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) standards. Conclusion  Submandibular gland fistula is a rare entity. It can be confused with close differentials, including branchial fistulas, if not thoroughly examined. Discharge from fistulae along with submandibular pain/tenderness and/or swelling are important diagnostic clues. A history of trauma, nodule at the site of discharge, prior submandibular disease/calculi, or discharge aggravated with food further increases a clinical suspicion. Optimal radiological investigation looking for calculi/foreign body and delineating the fistula tract is vital to affirm a diagnosis. Gland with fistula excision is a commonly advocated treatment of choice with no reports of recurrence, although conservative management and gland preserving surgery have also reported a favorable prognosis.


Introduction
Branchial fistulas are the most common differential for a lateral neck fistula. 1 Salivary gland fistulas are relatively less common and are mostly limited to the parotid gland. 2 A submandibular gland fistula (SGF) is extremely rare and can often be clinically confused with branchial fistula and other close differentials.
Certain clinical clues and radiological findings can help achieve a confirmatory diagnosis even prior to surgical exploration or histopathological examination.This will aid clinicians in optimal surgical planning and avoid irrelevant investigations/interventions.

Review of Literature Case presentation
An 18-year-old female presented with intermittent wateryto-purulent discharge from a small opening over the right submandibular neck region for 6 years.She had history of a small nodule over the same site, which had been previously  manipulated by a local doctor.Since then, she noticed intermittent discharge from the opening that became profuse while eating or when she was exposed to the smell of food.It was associated with pain over the right submandibular neck region.On examination, a small opening was noted just lateral to the greater horn of the hyoid bone.Expression of serous discharge was noted on gentle palpation of the surrounding neck region.No signs of lymph nodal disease or stigmata of granulomatous disease were noted.Based on these findings, a clinical diagnosis of salivary fistula was suspected and a computed tomography (CT) with fistulography was performed after instilling the dye from the cutaneous opening.Computed tomography fistulography showed a vertical tract communicating with the right submandibular gland parenchyma.Multiple intraglandular dilated branching tracts (corresponding to salivary gland ductules) were also noted converging into a horizontal tract (Wharton duct) that communicated with the floor of the mouth (►Fig.1A and 1B).Diluted methylene blue dye was instilled through the cervical opening and was found extruding intraorally from the right Wharton duct ostia.These findings confirmed a diagnosis of right submandibular gland cutaneous fistula.The entire fistula tract with surrounding neck skin was excised along with the right submandibular salivary gland under general anesthesia (►Fig.2A and 2B).Submandibular Gland Fistula Dokania et al.
Histopathological examination of the excised surgical tissue showed a fistula tract lined by squamous epithelium.The deeper aspects of the tract showed a sparse chronic inflammatory infiltrate of lymphocytes and histiocytes in the surrounding stroma.The submandibular gland showed a sparse aggregate of lymphocytes in several lobules and around mildly dilated ducts (►Fig.3A and 3B).

Methods
A comprehensive review of the literature was performed using PubMed and Google Scholar database in September 2022 and reported in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) standards (►Fig. 4).The database was searched for full-length articles using a combination of keywords, submandibular gland fistula, AND submandibular fistula, AND submandibular AND fistula and compatible with submandibular gland/duct fistula.The content of each article was reviewed in order to identify the studies relevant to the topic.Cases with fistulae arising from aberrant/ectopic glands were excluded.Only articles published in English literature and confined to humans were included.No age limits were applied.Information from the included articles and an illustrative case were collected in a predesigned Microsoft excel spreadsheet (Microsoft Corp., Redmond, WA, USA).Continuous variables were summarized with mean and standard deviation (SD).Nominal variables were summarized with frequency and percentage.No other statistical tests were done.
Clinical manifestation varied with the site of fistula opening and associated etiology.External fistulae mostly presented with serous/mucoid/mucopurulent discharge from the opening, which can sometimes be related to food.Eleven out of a total of 12 patients (91.67%) with external cutaneous opening complained of discharging fistulae.Only one case of external cutaneous fistula did not mention symptom of discharge (Kusunoki et al.).Most patients with calculi/foreign body as etiology presented with obstructive complaints of pain/tenderness or swelling in the submandibular region.Out of 9 cases with sialolith/ductal foreign body, 7 (77.78%)presented with either both or isolated symptom of pain/tenderness and/or swelling over the submandibular site.The remaining two cases of calculi/foreign body only presented with discharge (Knezević et al. and Saha et al.).
and CT scan/CT fistulography.In the remaining three cases, no radiological investigation was done.In these 15 cases, a radiological diagnosis of fistula was made in only 6 patients (40%).Amongst the 9 cases with actual calculi, a radiological detection was made in 6 cases (66.7%).
Gland excision with removal of fistula and/or calculi was the most commonly advocated treatment (55.6%).Gland preserving surgery and conservative management were less commonly performed and both were utilized in 22.2% of cases.

Ethics Approval
Not necessary for this research.

Fig. 1
Fig. 1 Important computed tomography fistulography findings.(A) Sagittal view: a vertical tract extending from the neck skin to the intraglandular parenchyma corresponding with sialo-cutaneous fistula, and a horizontal tract converging from the intraglandular region that represents the Wharton duct.(B) Axial view: Horizontal tract extending from the submandibular gland till the floor of the mouth, consistent with Wharton duct.

Fig. 2 Fig. 3
Fig. 2 Intraoperative findings.(A) Fistula tract (black arrow) noted communicating with the underlying submandibular gland (black star).(B) Excised fistula (red arrow) with the rim of the surrounding skin on one end and submandibular gland on the other end.

Fig. 4
Fig. 4 Literature search flow diagram based on the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) standards.

Table 1
Summary of cases of submandibular gland fistula International Archives of Otorhinolaryngology © 2023.Fundação Otorrinolaringologia.All rights reserved.Submandibular Gland Fistula Dokania et al.

Table 2
Etiology, clinical findings, radiological features, and advocated treatment amongst the reported cases of submandibular gland fistula Total number of cases amenable to radiological investigations in which fistula were detected.□ Total number of calculous causes of fistula in which calculi were detected radiologically.