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Mesothelial Hyperplasia

Notes: When irritated or injured, the mesothelial lining of the peritoneal cavity can show focal or diffuse hyperplasia. Some of the situations where mesothelial hyperplasia may be encountered include: hernia sacs (especially in children), hydroceles, cirrhosis, collagen vascular diseases, long-standing effusion of any cause, acute appendicitis, ruptured ectopic pregnancy. The hyperplastic mesothelium may form papillary structures, tubulo-glandular formations, or solid nests. There may be accompanying stromal reaction simulating desmoplastic response to invasive tumor.

When taken out of context, mesothelial hyperplastic changes, especially when florid, may be mistaken for mesothelioma or invasive carcinoma. Features favoring malignant mesothelioma over reactive mesothelial hyperplasia include: grossly visible papillary lesions, nuclear anaplasia, and the presence of necrosis. Immunohistochemistry is of little help in this distinction. On the other hand, immunostains can be quite helpful in distinguishing between reactive mesothelial hyperplasia and serosal implants in patients with borderline or malignant ovarian serous tumors.