Endometriosis of the appendix: prevalence, associated lesions, and proposal of pathogenetic hypotheses. A retrospective cohort study with prospectively collected data

Objective: To assess the prevalence of endometriosis of the appendix and the association with other pelvic localizations of the disease and to provide pathogenesis hypotheses. Methods: Monocentric, observational, retrospective, cohort study. Patients undergoing laparoscopic endometriosis surgery in our tertiary referral center were consecutively enrolled. The prevalence of the different localizations of pelvic endometriosis including appendix involvement detected during surgery was collected. Included patients were divided into two groups based on the presence of appendiceal endometriosis. Women with a history of appendectomy were excluded. Measurements and main results: Four hundred-sixty patients were included for data analysis. The prevalence of appendiceal endometriosis was 2.8%. In patients affected by endometriosis of the appendix, concomitant ovarian and/or bladder endometriosis were more frequently encountered, with prevalence of 53.9% (vs 21.0% in non-appendiceal endometriosis group, p = 0.005) and 38.4% (vs 11.4%, p = 0.003), respectively. Isolated ovarian endometriosis was significantly associated to appendiceal disease compared to isolated uterosacral ligament (USL) endometriosis or USL and ovarian endometriosis combined (46.2% vs 15.4% vs 7.7%, p < 0.001). Poisson regression analysis revealed a 4.1-fold and 4.4-fold higher risk of ovarian and bladder endometriosis, respectively, and a 0.1-fold risk of concomitant USL endometriosis in patients with appendiceal involvement. Conclusion: Involvement of the appendix is not uncommon among patients undergoing endometriosis surgery. Significant association was detected between appendiceal, ovarian, and bladder endometriosis that may be explained by disease dissemination coming from endometrioma fluid shedding. Given the prevalence of appendiceal involvement, counseling regarding the potential need for appendectomy during endometriosis surgery should be considered.