JPC SYSTEMIC PATHOLOGY
DIGESTIVE SYSTEM
September 2021
D-M18

 

Signalment: (JPC #3080866):  Dog, breed and sex unspecified

 

HISTORY:  None

 

HISTOPATHOLOGICAL DESCRIPTION: Salivary gland, submandibular: Replacing 90% of the salivary adenomeres and extending into the surrounding tissue is a proliferation of variably mature fibrous connective tissue admixed with small capillaries oriented perpendicularly to the surface (granulation tissue), which forms multiple pseudocysts.  Multifocally embedded within the connective tissue wall of the pseudocyst and within the pseudocyst lumina, are circular bodies of concentrically lamellated, eosinophilic, fibrillar concretions (sialoliths) that are up to 500 microns in diameter and are bounded by a thin rim of fibrous connective tissue and fibroblasts.  The center of multifocal sialoliths contain abundant, intensely basophilic, granular material (mineral).  Multifocally within the fibroadipose tissue adjacent to the sialoliths, there are multiple trabeculae of woven bone (osseous metaplasia) surrounded by either a thin rim of connective tissue or granulation tissue admixed with large numbers of macrophages, aggregates of lymphocytes and plasma cells, few neutrophils, or rare osteoclasts. Adjacent remaining salivary gland epithelium is often degenerate, characterized by swollen, vacuolated cytoplasm, and is infiltrated by numerous plasma cells and fewer lymphocytes.

 

MORPHOLOGIC DIAGNOSIS: Salivary gland:  Pseudocysts, focally extensive, with granulomatous inflammation, granulation tissue, fibrosis, multiple sialoliths, osseous metaplasia, and lymphoplasmacytic sialoadenitis (salivary mucocele/sialocele).

 

GENERAL DISCUSSION:

• Ranula
  • Cyst: lined by epithelium
  • Distention of the duct of the sublingual or submaxillary salivary gland along the floor of the mouth
• Mucocele / Sialocele (dogs)
  • Pseudocyst: not lined by epithelium
  • Most common salivary gland disease; sublingual gland > zygomatic > parotid
  • Accumulation of salivary secretions in single or multiloculated cavities in the soft tissues of the mouth or neck
  • Dogs 2-4 years old, as young as 6 months; more prevalent in German shepherd dogs and miniature poodles
  • Often secondary to blockage of the duct
  • Sublingual salivary gland – cervical, sublingual, or pharyngeal mucoceles
• Sialoliths (rare)
  • Predominately occur in the parotid duct; one report of a sublingual sialolith
  • Mostly composed of calcium carbonate with occasional magnesium ammonium phosphate and magnesium carbonate
  • Single, cylindrical, and often lodge at or near the orifice
  • Most common in horses

 

PATHOGENESIS:

• Trauma / duct blockage (e.g. sialolith, impacted food, foreign bodies, infection resulting in stricture) à saliva retention à glandular atrophy à infection and/or inflammatory response à acinar swelling à rupture à sialocele
• Sialoliths – pathogenesis is unclear; theories include:
  • Foreign bodies/material à glandular inflammation à exudate and/or sloughed cells à nidus for mineralization à sialolith
  • Ascending opportunistic bacterial infection à ductal metaplasia à stasis à accumulation of calcareous debris à sialolith
  • Microlith formation is apparently common and usually resolves; however, occasionally there may be decreased secretory activity and material accumulates, microliths enlarge and cause obstruction

 

TYPICAL CLINICAL FINDINGS:

• Cervical sialocele – acute, painful, subcutaneous mass progressing to a fluid-filled, non-painful mass in the intermandibular area or ventral neck
• Sublingual sialocele – blood-tinged saliva, abnormal prehension or reluctance to eat
• Pharyngeal sialocele – respiratory distress
• Parotid sialocele – acute, non-painful mass that progresses in size and becomes painful and firm
• Zygomatic sialocele – local swelling and possible exophthalmus

 

TYPICAL GROSS FINDINGS:

• Variably sized, subcutaneous, fluctuant mass with a wall of soft, pliable connective tissue that is well-vascularized
• Fluid is viscous and clear or blood tinged with low numbers of nucleated cells

 

TYPICAL MICROSCOPIC FINDINGS:

• Immature (sialocele) – wall of granulation tissue, pleocellular inflammatory response and amorphous, amphophilic material
• Mature (sialocele) – fibrous connective tissue, mononuclear inflammatory response with plasma cells predominating and the center becoming basophilic
• Sialoliths – small mineral concretions
• Atrophy of the salivary gland

 

ADDITIONAL DIAGNOSTIC TESTS:

• Fine needle aspirate
• Highly vacuolated macrophages
• Bloody fluid with erythrophagocytosis, hematoidin crystals (yellow rhomboid crystals), and windrowing of red blood cells
• Diffuse blue background (mucus)

 

DIFFERENTIAL DIAGNOSIS:

• Intermandibular cysts
• Thyroglossal duct cyst
• Cystic salivary adenoma
• Branchial pouch cyst
• Facial swelling – neoplasia, trauma, abscess, dental disease

 

COMPARATIVE PATHOLOGY:

• Equine – calculi are the most common salivary gland lesion despite being rare; the parotid gland is the most common site
• Ox – small sialoceles on the side of the tongue
• Ferret – sialoceles commonly present as facial swelling at the commissures of the mouth or orbital area
• NHP – rare reports of sialoliths resulting from foreign bodies

 

REFERENCES:

1. Caswell JL, Williams KJ. Respiratory system. In: Maxie MG, ed. Jubb, Kennedy, and Palmer’s Pathology of Domestic Animals. Vol 2. 6th ed. St. Louis, MO: Saunders Elsevier; 2016:477.
2. Geldberg HB. Alimentary system and the peritoneum, omentum, mesentery, and peritoneal cavity. In: McGavin MD, Zachary JF, eds. Pathologic Basis of Veterinary Disease. 6th ed. Louis, MO: Elsevier; 2017:353.
3. Orkin JL, Braswell LD. Sialolithiasis in two chimpanzees. J Am Vet Med Assoc. 1990;196(10):1651-1653.
4. Parslow A, Taylor DP, Simpson DJ. Clinical, computed tomographic, magnetic resonance imaging, and histologic findings associated with myxomatous neoplasia of the temporomandibular joint in two dogs. J Am Vet Med Assoc. 2016; 249(11):1301-1307.
5. Rooney JR, Robertson JL. Equine Pathology. Ames, IA: Iowa State University Press; 1999:65.
6. Steiner J. Gastrointestinal disease. In: Ettinger SJ, Feldman EC, Cote E, eds. Textbook of Veterinary Internal Medicine. Vol 2. 8th ed. St. Louis, MO: Elsevier-Saunders; 2017:1474.
7. Uzal FA, Plattner BL, Hostetter JM. Alimentary system. In: Maxie MG, ed. Jubb, Kennedy, and Palmer’s Pathology of Domestic Animals. Vol 2. 6th ed. St. Louis, MO: Saunders Elsevier; 2016:29.

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