Theories of endometriosis

Endometriosis is characterised by the presence of abnormally located tissue resembling the endometrium with glands and stroma. Several hypotheses have attempted to explain the development of such tissue. The oldest theory, th at of metaplasia. suggests that under diverse influences coelomic tissue co uld be transformed into endometrium. The most often cited theory, that of i mplantation, proposes that the physiological phenomenon of endometrial refl ux in the fallopian tubes during menstruation may, in certain conditions, o vercome local defense mechanisms, implant, and proliferate. The peritoneal fluid in unaffected women possesses the capacity to prevent endometriotic t issue from becoming established. The reasons for the occurrence of endometr iosis and its consequences (pain, sterility, adhesions) are probably numero us and involve the endometrium, the immune system (macrophages, natural kil ler cells), the peritoneum, and fallopian tubes. The failure to clear the p eritoneal cavity of fragments of endometrium could cause a state of local i nflammation with hyperactivation of macrophages secreting a variety of diff erent compounds. Some of these compounds may briny about metaplasia of the peritoneum or the development of Mullerian residues. (C) 2001 Elsevier Scie nce Ireland Ltd. All rights reserved.