Deeply infiltrating endometriosis: pathogenetic implications of the anatomical distribution

BACKGROUND: To investigate whether knowledge of the anatomical distribution of histologically proven deeply infiltrating endometriosis (DIE) lesions contributes to understanding the pathogenesis. METHODS: Observational study between June 1992 and December 2004 (retrospective study between 1992 and 2000; prospective study between 2001 and 2004). Continuous series of 426 patients suffering from pelvic pain who underwent complete surgical exeresis of DIE. DIE lesions were classified according to four different possibilities: (i) Firstly, DIE lesions were classified as located in the anterior or posterior pelvic compartment. (ii) Secondly, DIE were classified as left, median and right. (iii) Thirdly, DIE lesions were classified as pelvic or abdominal. (iv) Fourthly, DIE lesions that could present in a right and/or left location were classified as unilateral or bilateral. RESULTS: These 426 patients presented 759 histologically proven DIE lesions: bladder (48 lesions; 6.3%); uterosacral (USL) (400 lesions; 52.7%); vagina (123 lesions; 16.2%); ureter (16 lesions; 2.1%) and intestine (172, 22.7%). DIE lesions are significantly more often located in the pelvis (n=730 lesions) than in the abdomen (n=29 lesions) (P<0.0001). Pelvic DIE lesions are significantly more often located in the posterior compartment of the pelvis [682 DIE lesions (93.4%) versus 48 DIE lesions (6.6%); P<0.0001]. Pelvic DIE lesions are significantly more frequently located on the left side. For patients with unilateral pelvic DIE lesions, the anatomical distribution is significantly different in the three groups: left (172 lesions; 32.0%), median (284 lesions; 52.8%) and right (82 lesions; 15.2%) (P<0.0001). For patients with lateral lesions, left DIE lesions (172 lesions; 67.8%) were found significantly more frequently than right DIE lesions (82 lesions; 32.2%) (P<0.0001). A similar predisposition was observed when we included patients with bilateral pelvic DIE lesions (P=0.0031). The same significantly asymmetric distribution is observed for total (pelvic and abdominal) DIE lesions. CONCLUSIONS: Our results demonstrate that distribution of DIE lesions is asymmetric. It is possible that this is related to the anatomical difference between the left and right hemipelvis and to the flow of peritoneal fluid. These findings support the hypothesis that retrograde menstruation of regurgitated endometrial cells is implicated in the pathogenesis of DIE.