JPC SYSTEMIC PATHOLOGY

DIGESTIVE SYSTEM

September 2024

D-M12 

 

SIGNALMENT (JPC #2694985): Dog, age and breed unspecified

 

HISTORY: Unknown

 

HISTOPATHOLOGIC DESCRIPTION: Salivary gland, submandibular: Affecting 50% of the section is a well-demarcated area of coagulative necrosis characterized by retention of tissue architecture with a loss of differential staining (infarct), admixed with occasional multifocal areas of moderate hemorrhage, fibrin, edema, basophilic granular mineral, moderate numbers of neutrophils, and eosinophilic and karyorrhectic debris (lytic necrosis) which multifocally extends into the interlobular interstitium and adjacent capsule. The capsule is multifocally mildly thickened by increased numbers of small-caliber blood vessels oriented perpendicularly to reactive fibroblasts (granulation tissue), edema, and fibrous connective tissue. At the margin of the infarct between the infarct and viable salivary gland, there is a marked increase in the number of salivary ducts (duct hyperplasia) that are surrounded and separated by variably mature fibrous connective tissue. These ducts are often lined by degenerate epithelial cells with swollen, pale, vacuolated cytoplasm (degeneration) that occasionally pile up and fill the duct lumen (hyperplasia), or by multiple layers of flattened epithelium (squamous metaplasia) with lumens filled by a small amount of edema, secretory product, and degenerate neutrophils. 

 

MORPHOLOGIC DIAGNOSIS: Salivary gland, submandibular: Coagulative necrosis, acute, focally extensive (infarct), with foci of lytic necrosis and ductular hyperplasia with degeneration and squamous metaplasia, breed unspecified, canine.

 

CONDITION: Salivary gland infarction, canine necrotizing sialometaplasia

 

GENERAL DISCUSSION: 

• Rare, focally extensive to diffuse, ischemic necrosis of salivary adenomeres often secondary to infarction
• Reported in dogs (primarily small breed terriers), and cats
• Primarily involves the mandibular salivary gland, typically unilateral
• Dogs treated with sialectomy alone or nonsurgical methods have poor clinical outcomes often resulting in euthanasia; sometimes anticonvulsant medications help

 

PATHOGENESIS:

• Unknown (possibly trauma, infection, or hypersensitivity etiology)
• Vascular compromise due to trauma has been suggested
• Positive staining for IgG and C3 within vessel walls in one case suggests the possibility of a type-III hypersensitivity reaction and an immune-mediated etiology
• In one reported case of systemic disease with Bartonella henselae and B. vinsonii subsp. berkhoffii infection, granulomatous inflammation, necrosis and ductal squamous metaplasia were noted in salivary glands

 

TYPICAL CLINICAL FINDINGS:

• Vomiting, anorexia, gagging, ptyalism, weight loss
• Submandibular swelling and pain
• +/- Leukocytosis with neutrophilia, monocytosis, lymphopenia

 

TYPICAL GROSS FINDINGS: 

• Glands may be enlarged, hard, and hemorrhagic
• Thickened capsule and dry cut surfaces

 

TYPICAL LIGHT MICROSCOPIC FINDINGS:

• Well-demarcated areas of coagulative necrosis of acinar cells
• Necrotic tissue is bordered by a band of congestion, hemorrhage, neutrophils, macrophages, and lymphocytes
• Ductal hyperplasia and squamous metaplasia; can be mistaken for neoplasia, stains strongly with cytokeratin confirming epithelial origin
• Vascular thrombosis
• Vessels in necrotic areas may have fibrinoid necrosis of the tunica media and thrombosis
• Variable degrees of fibroplasia
• Cytology: Mixed salivary glandular cells, pleomorphic spindle cells, and rafts of mononuclear epithelioid cells with increased numbers of neutrophils

 

DIFFERENTIAL DIAGNOSIS:

Grossly enlarged and hemorrhagic salivary gland:

• Salivary neoplasia (SCC, adenocarcinoma, carcinoma, adenomas) 

• Note squamous metaplasia of ducts often easily mistaken for malignant transformation histologically 

• Sialoadenitis (inflammatory cells, mucus, purulent material), sialocele/salivary mucocele (pseudocyst, not lined by epithelium; more common)

Squamous metaplasia:

 

COMPARATIVE PATHOLOGY:

• Similar lesions have been reported in cats
• Histologically resembles a condition described in humans known as necrotizing sialometaplasia (NS), which generally resolves spontaneously

 

REFERENCES:

1. Brooks D, Hottinger H, Dunstan R. Canine necrotizing sialometaplasia: a case report and review of the literature. J Am Anim Hosp Assoc. 1995;31:21-25.
2. Brown PJ, Bradshaw JM, Sozmen M, Campbell RH. Feline necrotizing sialometaplasia: a report of two cases. J Feline Med Surg. 2004;6(4):279. 
3. Kim HY, Woo GH, Bae YC, Park YH, Joo YS. Necrotizing sialometaplasia of the parotid gland in a dog. J Vet Diagn Invest. 2010;22(6):975-977.
4. Allison RW, Walton RM. Subcutaneous Glandular Tissue: Mammary, Salivary, Thyroid, and Parathyroid. In: Valenciano AC, Cowell RL, eds. Diagnostic Cytology and Hematology of the Dog and Cat. 5th ed. St. Louis, MO: Elsevier Mosby; 2020:110- 111. 
5. Lieske DE, Rissi DR. A retrospective study of salivary gland diseases in 179 dogs (2010-2018). J Vet Diagn Invest. 2020;32(4):604-610.
6. Spagnoli ST, Gelberg HB. Alimentary System and the Peritoneum, Omentum, Mesentery, and Peritoneal Cavity. In: Zachary JF, ed. Pathologic Basis of Veterinary Disease. 7th ed. St. Louis, MO: Elsevier; 2022:425. 
7. Uzal FA, Platter BL, Hostetter JM. Alimentary System. In: Maxie MG, ed. Jubb, Kennedy, and Palmer’s Pathology of Domestic Animals. 6th ed. St. Louis, MO: Elsevier; 2016: 30.

 

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