Whole explants of peritoneum and endometrium: a novel model of the early endometriosis lesion.

OBJECTIVE: To determine whether whole fragments of endometrium can adhere to peritoneum with intact mesothelium.
DESIGN: Tissue culture and immunohistochemical study.
SETTING: University medical center. PATIENT(S): Reproductive-age women undergoing surgery for benign conditions. INTERVENTION(S): 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 MEASURE(S): Adhesion of endometrial fragments to the surface of the peritoneum was evaluated. Adherent endometrium was identified with the use of the dissecting microscope and by the performance of serial sections of the peritoneum explants. Immunohistochemical staining of the mesothelium with antibodies to cytokeratin was used to ensure an intact layer of mesothelium beneath the endometrial implants. Transmission electron microscopy also was used to evaluate this adhesion process. RESULT(S): Endometrium was identified attached to the surface of the peritoneum. Most of the 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. Endometrial stromal cells, and not epithelium, attached to the mesothelium. CONCLUSION(S): Endometrium can attach to the mesothelial surface of the peritoneum. Endometrial stromal cells are involved in this attachment. Invasion through the mesothelium seems to occur rapidly.