Epithelial cysts (Figure 1 and Figure 2) are seen occasionally in mice and are rarely seen in rats. These cysts are considered to arise from downgrowth of the surface epithelium of the ovary. The cysts are lined by flattened, cuboidal, columnar, or squamous epithelium; squamous epithelium may be keratinized. The lining epithelium may resemble that of the surface epithelium.
Ovarian epithelial cysts should be diagnosed, but cysts occurring as background lesions need not be graded. In the case of an epithelial cyst, the diagnosis should include the type of cyst as a modifier (i.e., Ovary - Cyst, Epithelial). If the cysts are thought to be treatment related, they may be graded to fully characterize the treatment effect. If applicable, the terms "bilateral" and "multiple" may be included in the diagnosis.
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