Is ureteral endometriosis an asymmetric disease?

Six cases of endometriosis obstructing the left ureter were observed among 1054 consecutive patients undergoing surgery in an eight-year period. In ad dition, 125 women with ureteral endometriosis (left-sided, n = 66; right-si ded, n = 40; bilateral, n = 19) were described in 62 articles identified in a systematic review of the English language literature between 1980 and 19 98. Considering only the patients with unilateral ureteral endometriosis an d combining the published figures with those of our surgical series, the ob served proportion of left lesions (72/112, 64%; 95% CI 55% to 73%) was sign ificantly different from the expected proportion of 50% (chi(1)(2), 9.14, P = 0.002). The lateral asymmetry found in the location of ureteral endometr iosis is compatible with the menstrual reflux theory and with the anatomica l differences of the left and right hemipelvis.