[Definition, description and classification of endometriosis].

The presence of ectopic endometrial tissue defines endometriosis. External endometriosis, the real one, can be observed everywhere in the woman body and in genitourinary tract in man. Macroscopic and histologic features depend on their duration, on their location and the period of the menstrual cycle. All the changes of eutopic endometrium can be exhibited by endometriotic foci: response to hormonal stimuli, decidualization, malignant transformation (neoplasm arising from endometriosis).... The revised American Fertility Society classification, most frequently used, establishes scores assigned to ovarian and peritoneal lesions. Adenomyosis or internal endometriosis involves the myometrium. This peculiar entity represents a diverticulosis of the endometrium into myometrium with smooth muscle hyperplasia.