Laterality and asymmetry of endometriotic lesions

OBJECTIVE: To identify possible sources of heterogeneities in the estimation of the proportion of bilateral cases and of left-sided cases of endometriotic lesions. DESIGN: We included 20 studies that reported estimated proportions, and examined the effect of sample size and the anatomic location of lesions on the heterogeneity using a mixed-effect logit regression model. SETTING: Academic. PATIENT(S): None. INTERVENTION(S): None. MAIN OUTCOME MEASURE(S): None. RESULT(S): The sample size of these studies ranged from 64 to 1,407, with a median of 227 and a total sample size of 7,236 cases. There is substantial heterogeneity in the estimated proportion of both bilateral and left-sided cases. The estimated proportion of bilateral cases is positively associated with the sample size of the study, whereas that of left-sided cases is negatively associated with the sample size, irrespective of the anatomic locations of endometriotic lesions. CONCLUSION(S): There is an identifiable source of heterogeneity in proportion estimates, with the sample size being an apparent source. Although the precise causes for the sample size dependency are unclear, it is possible that the invasive nature of endometriotic lesions may eventually render most cases bilateral. Moreover, there are both promoting as well as mitigating or negating factors that contributing to the asymmetry of endometriotic lesions.