Alimentary System

Salivary Gland, Duct - Metaplasia, Squamous

Narrative
Comment:
Metaplasia is a change in which one terminally differentiated cell type is replaced by another cell type of the same germ line. Usually, a specialized type of epithelium is replaced by less specialized type of epithelium. Metaplasia is often, but not always, an adaptive change that occurs in response to repeated epithelial damage and is therefore often accompanied by other lesions such as inflammation or necrosis. Squamous metaplasia may be reversible if the cause is removed. Squamous metaplasia is a common form of metaplasia, presumably because squamous epithelium is more resistant to damage than other forms of epithelia. Squamous metaplasia is usually the result of chronic irritation, but it can have other causes (e.g., hypovitamnosis A). In the salivary ducts, metaplasia of the normally cuboidal ductal epithelium to stratified squamous epithelium has been seen in response to chemicals, ionizing radiation, viral infections, vitamin A deficiency, and blockage of ducts by salivary calculi. Squamous metaplasia of the ductular epithelium may be a preneoplastic lesion progressing to squamous cell carcinoma.
Recommendations:
Squamous metaplasia of the salivary duct should be diagnosed and graded based on the number of areas involved and the thickness of the squamous epithelium. Associated lesions, such as inflammation, necrosis, or degeneration, should be diagnosed separately.
References:

Greaves P. 2007. Digestive system. In: Histopathology of Preclinical Toxicity Studies, 3rd ed. Academic Press, London, 334-456.

Abstract: http://www.sciencedirect.com/science/book/9780444527714

Myers RK, McGavin MD. 2007. Cellular and tissue responses to injury. In: Pathologic Basis of Veterinary Disease, 4th ed (McGavin MD, Zachary JF, eds). Mosby, St Louis, MO, 14-62.

National Toxicology Program. 1990. NTP TR-340. Toxicology and Carcinogenesis Studies of Iodinated Glycerol (CAS No. 5634-39-9) in F344/N Rats and B6C3F1 Mice (Gavage Studies). NTP, Research Triangle Park, NC.

Abstract: https://ntp.niehs.nih.gov/go/10786

Neuenschwander SB, Elwell MR. 1990. Salivary glands. In: Pathology of the Fischer Rat (Boorman GA, Montgomery CA, MacKenzie WF, eds). Academic Press, San Diego, CA, 31-42.

Abstract: https://www.ncbi.nlm.nih.gov/nlmcatalog/9002563
  • Image of metaplasia, squamous in the salivary gland duct from a male F344/N rat in a chronic study

    Salivary gland, Duct - Metaplasia, Squamous in a male F344/N rat from a chronic study. The normally cuboidal ductal epithelial cells have been replaced by stratified squamous epithelium (arrow).

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Salivary gland, Duct - Metaplasia, Squamous in a male F344/N rat from a chronic study. The normally cuboidal ductal epithelial cells have been replaced by stratified squamous epithelium (arrow).
Salivary gland, Duct - Metaplasia, Squamous in a male F344/N rat from a chronic study. The normally cuboidal ductal epithelial cells have been replaced by stratified squamous epithelium (arrow).
Salivary gland, Duct - Metaplasia, Squamous in a male F344/N rat from a chronic study (higher magnification of Figure 1). The normally cuboidal ductal epithelial cells have been replaced by stratified squamous epithelium.
Salivary gland, Duct - Metaplasia, Squamous in a male F344/N rat from a chronic study (higher magnification of Figure 1). The normally cuboidal ductal epithelial cells have been replaced by stratified squamous epithelium.
Salivary gland, Duct - Metaplasia, Squamous in a male F344/N rat from a chronic study. The normally cuboidal ductal epithelial cells have been replaced by stratified squamous epithelium (arrow).
Salivary gland, Duct - Metaplasia, Squamous in a male F344/N rat from a chronic study. The normally cuboidal ductal epithelial cells have been replaced by stratified squamous epithelium (arrow).
Salivary gland, Duct - Metaplasia, Squamous in a male F344/N rat from a chronic study (higher magnification of Figure 3). The normally cuboidal ductal epithelial cells have been replaced by stratified squamous epithelium.
Salivary gland, Duct - Metaplasia, Squamous in a male F344/N rat from a chronic study (higher magnification of Figure 3). The normally cuboidal ductal epithelial cells have been replaced by stratified squamous epithelium.
Salivary gland, Duct - Metaplasia, Squamous in a male F344/N rat from a chronic study. The normally cuboidal ductal epithelial cells have been replaced by stratified squamous epithelium (arrow).
Salivary gland, Duct - Metaplasia, Squamous in a male F344/N rat from a chronic study. The normally cuboidal ductal epithelial cells have been replaced by stratified squamous epithelium (arrow).
Salivary gland, Duct - Metaplasia, Squamous in a male F344/N rat from a chronic study (higher magnification of Figure 5). The normally cuboidal ductal epithelial cells have been replaced by stratified squamous epithelium.
Salivary gland, Duct - Metaplasia, Squamous in a male F344/N rat from a chronic study (higher magnification of Figure 5). The normally cuboidal ductal epithelial cells have been replaced by stratified squamous epithelium.

Authors:

Linda H. Kooistra, DVM, PhD, DACVP
Pathologist
Charles River Laboratories, Inc.
Research Triangle Park, NC

Abraham Nyska, DVM, Diplomate ECVP, Fellow IATP
Expert in Toxicologic Pathology
Visiting Full Professor of Pathology
Sackler School of Medicine, Tel Aviv University Timrat Israel

Reviewers:

Joel R. Leininger, DVM, PhD
Senior Pathologist
MedImmune
Washington, DC

Amy Brix, DVM, PhD, DACVP
Senior Pathologist
Experimental Pathology Laboratories, Inc.
Research Triangle Park, NC