Is cystic ovarian endometriosis an asymmetric disease?

Objective To investigate whether asymmetry exists in the left- and right-handed distribution of ovarian cystic lesions in a large series of women with endometriosis. Design Retrospective evaluation of a case series. Setting Tertiary care and referral academic centre for the study and treatment of endometriosis. Population A total of 1054 consecutive women undergoing first-line surgical treatment for endometriosis in an eight-year period. Methods Data were collected on indication for the intervention, age at surgery, parity and disease stage as well as side and size of ovarian endometriomas. Main outcome measure Frequency of left- and right-sided ovarian endometriomas. Results Histologically confirmed endometriotic ovarian cysts were present in 561 women, which were on the left side in 255 instances, on the right in 148, and bilateral in 158. In the patients with unilateral endometriomas, the observed proportion of left cysts (255/403, 63%; 95% confidence interval, 58% to 68%) was significantly different from the expected proportion of 50% (chi(1)(2), 28.41, P<0.001). Including also the bilateral endometriotic cysts gave a total of 413/719 (57%) left-sided and 306/719 right-sided endometriomas. The magnitude of these proportions did not vary appreciably during the eight years considered. The difference in proportion of left- and right-sided endometriotic cysts was virtually similar in subgroups of women with different indications for surgery. Cyst side was not related to age, parity or cyst diameter. Conclusions The finding of a lateral asymmetry in the occurrence of ovarian endometriotic cysts is compatible with the anatomical differences of the left and right hemipelvis and supports the menstrual reflux theory.