Asymmetry in distribution of diaphragmatic endometriotic lesions: evidence in favour of the menstrual reflux theory

BACKGROUND: If the menstrual reflux or implantation theory of endometriosis is true, refluxed endometrial cells could reach the right hypochondrium transported by the clockwise peritoneal fluid current and would implant more easily on the right diaphragmatic leaf as they are stuck there by the falciform ligament. METHODS: To investigate if a lateral asymmetry exists in diaphragmatic endometriotic lesion distribution, all articles on diaphragmatic endometriosis identified by MEDLINE, EMBASE and PUBMED database searches were retrieved, and additional reports were collected by systematically reviewing all references. The number of women and the side of the lesion with respect to the falciform ligament of the liver were obtained from individual studies, and the combined frequency of right- and left-side diaphragmatic endometriosis was computed. In addition, seven personal cases were described. RESULTS: There were 16 reports including 47 subjects selected. Diaphragmatic endometriosis was on the right side in 31 (66%) patients, on the left in 3 (6%) and bilateral in 13 (27%). In the personal series, lesions were on the right side in five cases, on the left in one and bilateral in one. Considering only unilateral lesions, the observed proportion of right-sided endometriotic implants (36/40) was 90% (95% CI 76-97%; chi(2)(1) 32.6, P < 0.0001). CONCLUSIONS: The observed major asymmetry in diaphragmatic endometriotic lesion distribution in favour of the right leaf supports the menstrual reflux theory.