Oral Mucosa - Cyst, Squamous

Image of cyst, squamous in the oral mucosa from a female F344/N rat in a chronic study
Oral mucosa - Cyst, Squamous in a female F344/N rat from a chronic study. There is a keratin-filled squamous cyst (arrow) beneath the mucosa in the hard palate.
Figure 1 of 3
Image of cyst, squamous in the oral mucosa from a female F344/N rat in a chronic study
Oral mucosa - Cyst, Squamous in a female F344/N rat from a chronic study (higher magnification of Figure 1). There is a keratin-filled squamous cyst (arrow) beneath the mucosa in the hard palate.
Figure 2 of 3
Image of cyst, squamous in the oral mucosa from a female F344/N rat in a chronic study
Oral mucosa - Cyst, Squamous in a female F344/N rat from a chronic study (higher magnification of Figure 1). The wall of the keratin cyst is composed of normal squamous epithelium.
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comment:

Squamous cysts ( Figure 1image opens in a pop-up window , Figure 2image opens in a pop-up window , and Figure 3image opens in a pop-up window ) are lined by well-differentiated, keratinized squamous epithelium, and the lumen usually contains keratin. Squamous cysts are congenital anomalies and therefore are considered incidental lesions. They are usually unilocular structures that may have hair follicles in the squamous epithelium lining the cyst. Possible differentials for this lesion are cystic keratinizing hyperplasia of the gingiva, periodontal pockets, and squamous cell carcinoma. Cystic keratinizing hyperplasia is characterized by areas in the gingiva in which the epithelium is markedly hyperplastic and raised in papillary folds, forming cyst-like spaces filled with keratin. The lesion is associated with areas of hyperplastic gingival epithelium adjacent to or near the cystic areas, whereas squamous cysts tend to be a single, isolated lesions with no association to areas of epithelial hyperplasia in the oral cavity. Periodontal pockets are similar to squamous cysts, but they are always located around the tooth, as they represent an abnormally deepened gingival sulcus. Periodontal pockets do not have hair follicles in the squamous epithelium lining the pocket. Squamous cell carcinomas are invasive, and the cells are pleomorphic and atypical and do not exhibit orderly maturation. (See Oral Mucosa - Hyperplasia, Cystic, Keratinizing and Tooth - Periodontal Pocket).

recommendation:

Squamous cysts are considered incidental background lesions but should be diagnosed when present for completeness sake. Cysts are generally not graded in NTP studies.

references:

Bertram TA, Markovits JE, Juliana MM. 1996. Non-proliferative lesions of the alimentary canal in rats GI-1. In Guides for Toxicologic Pathology. STP/ARP/AFIP, Washington, DC, 1-16.
Full Text: https://www.toxpath.org/docs/SSNDC/GINonproliferativeRat.pdf

National Toxicology Program. 2010. NTP TR-558. Toxicology and Carcinogenesis Studies of 3,3’,4,4’-Tetrachloroazobenzene (TCAB) (CAS No. 14047-09-7) in Harlan Sprague Dawley Rats and B6C3F1 Mice (Gavage Studies). NTP, Research Triangle Park, NC.
Abstract: http://ntp.niehs.nih.gov/go/33564