Evidence for asymmetric distribution of sciatic nerve endometriosis

OBJECTIVE: To investigate if a lateral asymmetry exists in the distribution of endometriotic lesions of the sciatic nerve. DATA SOURCES: All articles on sciatic nerve endometriosis identified by MEDLINE and EMBASE database searches were retrieved, and additional reports were collected by systematically reviewing all references. Monographs on endometriosis published in the last 15 years were consulted. METHODS OF STUDY SELECTION: We considered articles in which the presence of an endometriotic lesion of the sciatic nerve and the affected side were assessed. We also included reports lacking histological examination of sciatic nerve specimens but with a surgical diagnosis of pelvic endometriosis. Two authors abstracted data independently on standardized forms. The number of women and the side of the lesion were obtained from individual studies, and the combined frequency of left- and right-side sciatic nerve endometriosis in published reports was computed. TABULATION, INTEGRATION, AND RESULTS: Thirty-two reports including 63 subjects were selected. Endometriosis of the sciatic nerve was on the right side in 41 patients, on the left in 20, and bilateral in two. Considering only patients with unilateral sciatic nerve endometriosis, the observed proportion of right-side lesions (41 of 61 [67.2%]; 95% confidence interval 54.0%, 78.7%) significantly differed from the expected proportion of 50% (χ21 7.23, P = .007). Among the 16 cases of histological demonstration of endometriosis infiltrating sciatic nerve roots or fibers, ten had it on the right side (62.5%) and six on the left. Twenty-six of the 38 subjects (68.4%) with surgical demonstration of pelvic endometriosis but without histopathologic evidence of direct sciatic nerve involvement were affected by right cyclic sciatica. CONCLUSION: The finding that two thirds of patients with sciatic nerve endometriosis had right-side lesions constitutes further evidence against the coelomic metaplasia theory. The interposition of the sigmoid colon between the regurgitated endometrial cells implanted on the left posterolateral pelvic peritoneum seems to protect the left lumbosacral plexus and sciatic nerve.