Adenomyosis (Figure 1, Figure 2, Figure 3, and Figure 4) is the presence of normal or hyperplastic endometrial glands and stroma that extend into the myometrium. Occasionally epithelial cells can extend onto the serosal surface of the uterus. Hormonal imbalance is a key factor. It is more common in some strains of mice (B6C3F1) than in rats and is more common in aged mice. It is important to differentiate adenomyosis from neoplasms. Adenomyosis has no atypia of the epithelial cells, which is a useful distinguishing feature. Adenomyosis may be differentiated from adenocarcinoma by examining the epithelial cells and by the presence of normal uterine stroma. Malignant epithelial cells of adenocarcinomas exhibit cellular pleomorphism and often are multilayered. Adenomyosis should not be described as endometriosis, which is diagnosed only in primates (in endometriosis, the glands spread to the peritoneal cavity).
Uterus - Adenomyosis should be diagnosed and graded whenever present.
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