Spontaneous necrotizing sialometaplasia of the submandibular salivary gland in a Beagle dog

Abstract

A single mass was found on the left submandibular salivary gland at necropsy of a 15-month-old male commercially bred laboratory Beagle dog from a control dose group from a repeat toxicity study. Microscopically, the mass was composed of a well-demarcated area of coagulative necrosis surrounded and separated from the normal salivary gland tissue by a thick fibrovascular capsule. Necrosis was admixed with areas of hemorrhage, fibrin, edema, fibrinoid necrosis of the vascular tunica media, and thrombosis of small and large vessels. Within the necrotic tissue, there was marked ductal hyperplasia, and squamous metaplasia of duct and acinar epithelium. The mass was diagnosed as necrotizing sialometaplasia of the submandibular gland. Hyperplastic ductal elements and squamous metaplasia can be mistaken microscopically with squamous cell carcinoma. Therefore, pathologists should be aware of this lesion as to avoid errors in the diagnosis of this benign pathologic condition.

Keywords: Beagle dog; necrotizing sialometaplasia; submandibular salivary gland.

Fig. 1.

Necrotising sialometaplasia. Sub-gross appearance. Extensive coagulative necrosis of acini, haemorrhage and glandular hyperplasia of acini separated from viable tissue by a thick fibrovascular capsule. Hematoxylin and eosin stain. Bar = 4 mm.

Fig. 2.

Necrotising sialometaplasia. Coagulative necrosis of acini, hyperplasia and metaplasia of duct and acinar epithelium. Hematoxylin and eosin stain. Bar = 200 µm.

Fig. 3.

Necrotising sialometaplasia. Hyperplastic and metaplastic ducts surrounded by reactive fibrosis, and some duct lumens are filled with degenerate neutrophils and Periodic acid-Schiff (PAS) positive secretory product. Periodic acid-Schiff (PAS) stain. Bar = 100 µm.

Fig. 4.

Necrotising sialometaplasia. Fibrinoid necrosis and thrombosis (*) of a large vessel in the necrotic areas. Hematoxylin and eosin stain. Bar = 300 µm.

Fig. 5.

Necrotising sialometaplasia. Cytokeratin had stronger cytoplasmic immunoreactivity in the metaplastic squamous epithelium (right) compared to the normal glandular epithelium (left). Immunohistochemical stain for cytokeratin, diaminobenzidine chromogen and counterstained with hematoxylin. Bars = 100 µm.