Fistula of the Submandibular Gland Presenting as a Painful Mass in the Neck: A Rare Case.

Dear Editor:

Salivary gland fistula is an abnormal pathway involving the salivary gland or duct. Accurate diagnosis is achieved by observing clinical manifestations, radiographic findings, and surgical exploration. Dermatologists may be unfamiliar with salivary gland fistulas presenting as parotid fistulas or fistulas of the submandibular gland because there are no such case reports in dermatologic literatures. We report a rare case of fistula of the submandibular gland and provide a brief review of the literature.

We received the patient's consent form about publishing all photographic materials. A 53-year-old female presented with erythematous plaques and a painful, tender subcutaneous mass on the left side of the neck (Fig. 1A). She had been diagnosed with sialadenitis a week before and had a sore throat after undergoing endoscopy. We initially diagnosed her with pyoderma and performed a skin biopsy and computed tomography (CT) scan of the neck. Histopathologic results showed septal fibrosis with perivascular inflammatory infiltration in the mid-dermis and subcutaneous fat layer and no evidence of bacterial infection, including tuberculosis, on tissue culture and special stainings of Ziehl–Neelsen, periodic acid Shiff and gram stain (Fig. 1B, C). The CT scan revealed fuzzy enhancing tubular structures from the submandibular gland to the anterior part of the platysma muscle, consistent with symptoms of inflammation and fistula (Fig. 1D~F). Routine blood examination showed no significant findings. Based on these findings, we diagnosed her with fistula of the submandibular gland. It improved with conservative treatment using systemic antibiotics under close observation.

Fig. 1

Erythematous nodule on the left side of the neck (A). Histopathologic findings showed upper dermal edema with lymphocytes and neutrophils infiltration in the mid to deep dermis, hematoxylineosin (H&E) ×20 (B), H&E, ×400 (C). Computed tomography scan reavled fuzzy enhancing tubular structures (4 cm) from the left submandibular gland to the anterior aspect of the plastysma muscle (*), consistent with fistula and inflamation (D~F).

Salivary gland fistula usually originates from the parotid gland although it also rarely arises from the submandibular gland1. Most previous reports were limited to parotid gland fistula; only 13 cases describing fistula of the submandibular gland were found by using keyword, ‘submandibular gland fistula’, ‘submandibular fistula’, ‘submandibular’ and ‘fistula’ and compatible with submandibular gland fistula on PubMed searching (Table 1)2345. These cases listed causes of trauma1, sialadenitis2, calculi3, or structural anomaly4. Salivary gland fistula is caused by mechanical obstruction to the drainage of the salivary duct via natural pathways such as calculi or tumors pressing on the duct. Because our case showed no such anomaly, we thought it developed as a complication of sialadenitis. The precise pathogenesis of sialadenitis and fistula formation is currently unknown. The fistula tract in most cases communicated with other space such as paranasal sinus through internal openings or had external openings on the skin or oral cavity. Here, it connected the infected submandibular gland to the anterior part of the platysma muscle, thus penetrating the muscle. Only two of the previously reported 13 cases described a fistula with skin lesions showing cutaneous openings1. The opening in this case did not adhere to the skin, but was connected to the platysma muscle, presenting an erythematous nodule. It might be easily misdiagnosed, as it is extremely rare and the skin lesion may present without any cutaneous opening. Dermatologists should keep in mind the possibility of fistula of the submandibular gland when examining painful masses in the neck.

Table 1

Summary of case reports of submandibular gland fistula

Author (year)	Sex/age (yr)	Cause	Skin lesion	Treatment
Reuther and Hausamen2 (1973)	F/24	Chronic sialoadenitis	ND	Excision
De Geus et al. (1976)	M/8	High-voltage electrical burn	ND	Excision
Knezevic et al. (1983)	M/14	Foreign body	ND	Excision
Excision Asfar et al.3 (1989)	M/55	Salivary calculi	Swelling with fistula opening	Excision
Excision Asfar et al.3 (1989)	M/43	Salivary calculi	Tender nodule	Excision
Asfar et al.3 (1989)	M/75	Salivary calculi	Tender nodule	Excision
Bhuvanesh et al. (1995)	M/41	Gun shot wound	ND	Antibiotics
Antibiotics Avik et al. (2006)	M/10	Trauma	Fistulous opening	Excision
Excision Kulkarini et al. (2015)	M/45	Malignant tumor	Swelling with fistula opening	Excision
Excision Kieliszak et al.4 (2015)	M/20	Structural abnormality	ND	Excision
Kieliszak et al.4 (2015)	M/20	Structural abnormality	ND	Excision
Stanford et al. (2015)	F/56	Salivary calculi	ND	ND
Kusunoki et al.5 (2017)	M/72	Salivary calculi	Erythematous nodule with skin defect	Excision
Present case	F/53	Sialoadenitis	Erythematous nodule	Antibiotics

F: female, M: male, ND: not described.