An in vitro model to study the pathogenesis of the early endometriosis lesion.

Objective: To determine if whole fragments of endometrium can adhere to peritoneum with intact mesothelium.

Design: Tissue culture and immunohistochemical study.

Setting: University Medical Center.

Patients: Reproductive-age women undergoing surgery for benign conditions.

Interventions: Whole explants of human peritoneum from the anterior abdominal wall and the posterior surface of the uterus were cultured with whole fragments of mechanically dispersed endometrium.

Main Outcome Measures: Adhesion of endometrial fragments to the surface of the peritoneum was evaluated. Adherent fragments of endometrium were identified using the dissecting microscope and by performing serial sections of the peritoneum explants for light and confocal laser-scanning microscopy. Immunohistochemical staining of the mesothelium with antibodies to cytokeratin and vimentin was used to ensure an intact layer of mesothelium beneath the endometrial implants. Transmission electron microscopy was also used to evaluate the adhesion of endometrium to the mesothelium.

Results: Endometrium was identified attached to the surface of the peritoneum. After 18-24 hours of culture, the majority of implants did not have identifiable mesothelium beneath them, but most had intact mesothelium running up to the point of attachment. Approximately 10% of the endometrial implants had intact mesothelium at the site of attachment. After 1 hour of culture, both endometrial stromal and epithelial cells were attached to intact mesothelium in nearly all cases. Early transmesothelial invasion involves endometrial stromal cells.

Conclusions: Endometrial stromal and epithelial cells can attach to the intact mesothelial surface of the peritoneum. Endometrial stromal cell invasion through the mesothelium occurs in less than 18-24 hours.