Unusual ovarian, tubal and pelvic mesothelial inclusions in patients with endometriosis

Unusual mesothelial inclusions were observed in ovaries, fallopian tubes and pelvic wall in six out of 57 patients with endometriosis and in none of 100 ovaries without endometriosis. Although of the same origin as the common ovarian epithelial inclusion cysts, these mesothelial inclusions were different being small, closely packed mesothelial cell nests with or without central lumina and occasionally demonstrating a pseudoinfiltrative pattern, rather than the cystically dilated, non‐crowded glands lined by a variety of Mullerian type epithelia. Histochemical reactions of these mesothelial inclusions were similar to those obtained in normal mesothelium, but differed from those seen in common epithelial inclusion cysts, endometriosis and adenocarcinoma. The association of these inclusions with endometriosis suggests that a common stimulus is responsible for the development of both conditions from the multipotential pelvic mesothelium.