Limited hormonal responsiveness of ectopic endometrium: histologic correlation with intrauterine endometrium

In order to assess the hormonal responsiveness of ectopic endometrium, 438 unselected endometrial implants and corresponding intrauterine endometrium from 196 patients were evaluated and classified by standard endometrial dating criteria. Only 13% of the endometrial implants were histologically synchronous with the corresponding intrauterine endometrium. Both proliferative and secretory implants were present in relatively constant proportions throughout the menstrual cycle, demonstrating a lack of correlation with cyclic endogenous hormones. A significant percentage (range, 25% to 49%) of endometrial implants displayed some form of local hemorrhage irrespective of the menstrual cycle timing. Sixty percent of the patients had evidence of hemorrhage in at least one implant. In women receiving hormonal therapy at the time of surgery, the proportion of endometrial implants that were histologically in concert with the corresponding endometrium ranged from 0% to 33%. In early pregnancy and menopause, 50% and 31% of endometrial implants were histologically similar, respectively. These data indicate that the hormonal responsiveness of endometrial implants is unpredictable and inconsistent.