Lesson 56b: Common Salivary Disorders

Portals of entry

i. Hematogenous (bloodborne pathogens)

ii. Direct penetration by foreign objects

iii. Obstruction of the excretory ducts

iv. Bite wounds

v. Ascending infections from salivary ducts (in humans)

vi. Rabies virus is spread through saliva

vii. Serous portions of the salivary glands are radiosensitive

How is rabies spread by saliva?

Virus spreads to salivary glands via axonal transport using parasympathetic nerves (CN VII & IX) and sympathetic nerves in thoracic spinal cord segments T1 to T3

Saliva defense mechanisms

Electrolytes: Na+, K+, Ca2+, Mg-, Cl-, HCO3-, PO4-

Iodine, Mucus (lubricant), bacterial rich flora

Antibacterial compounds: Thiocyanate, hydrogen peroxide; secretory IgA

EGF (epidermal growth factor)

Digestive enzymes: α-amylase, lipase, kallikrein

Antimicrobial enzymes secreted in saliva

lysozyme, lactoperoxidase, proline-rich proteins, class A and B acid phosphatases, N-acetylmuramoyl-L-alanine amidase, NAD(P)H dehydrogenase (quinone), superoxide dismutase, glutathione transferase, class 3 aldehyde dehydrogenase, and glucose-6-phosphate isomerase

Dysfunction/responses to injury

1. Regeneration (incomplete), principally from ductular epithelium

2. Atrophy

3. Fibrosis

4. Squamous metaplasia of secretory epithelium: blockage of ducts → development of saliva-filled cysts (sialoceles)

5. Blockage of sublingual salivary glands: Ranula

Sialoadenitis - inflammation of the salivary glands

seen in rabies and canine distemper

Focal necrosis, mononuclear cell inflammation, and Negri bodies in the nuclei of ganglion cells (sometimes)

Sialodacryoadenitis

Salivary gland and some adnexal ocular structures

Coronavirus infection in the rat

Suppurative parotid sialoadenitis in pigs

Cause by Salmonella typhisuis

Clinical signs in inflammatory disorders

Gross lesions, Swelling and edema, Pain on palpation

Abscesses: 2º the migration of foreign bodies(grass awns)

in the retrobulbar zygomatic gland may cause proptosis

Ranula

Cystic saliva-filled distention of the duct of the sublingual or submaxillary salivary gland that occurs on the floor of the mouth alongside the tongue

Etiology: Idiopathic, Sialoliths

Salivary mucocele

Pseudocyst not lined by epithelium but filled with saliva

Etiology: Idiopathic or 2º to traumatic rupture of the duct of a sublingual salivary gland; leakage and encapsulation of saliva by reactive connective tissue

Sialoliths

Rare in domestic animal species

2º to sialoadenitis: Sloughed cells or inflammatory exudate forming a nidus for mineral accretion

can lead to Ranula formation

Salivary gland neoplasia

Benign and Malignant: uncommon but occur in all species

composed of: Glandular or Ductular elements, Combination of epithelial and mesenchymal components (as in mixed mammary neoplasms)

Diagnosis of salivary gland neoplasia

Salivary gland infarction (cats, dogs)

Grossly: Firmness and swelling

Microscopically: Discrete foci of parenchymal necrosis with peripheral hemorrhage and inflammatory cells

What can be mistaken for neoplasia?

Attempted incomplete regeneration of the gland from ductal epithelium

A 7-year-old dog presents with unilateral firm enlargement of the mandibular salivary gland. There is no fever. Ultrasound shows a poorly demarcated hypoechoic region. Histopathology reveals focal coagulative necrosis, peripheral hemorrhage, and proliferative ductular epithelium forming irregular gland-like structures. Mitotic figures are rare and cellular atypia is minimal. What is the MOST likely diagnosis?

C. Salivary gland infarction