Visible and Invisible (Occult) Endometriosis

Abstract

Endometriosis is a chronic disease characterized by endometrial tissue located outside of the uterine cavity and is associated with chronic pelvic pain and infertility. However, an in-depth understanding of the pathophysiology of endometriosis is still elusive. Once generated within pelvis due to retrograde entry of menstrual debris, peritoneal endometriotic lesions time-dependently change their color appearance resulting from certain biochemical change within lesions. A variable pattern of endometriotic lesions within pelvis can be detected by laparoscopy as visible peritoneal endometriosis. It is generally believed that besides ovarian steroid hormones, the growth of endometriosis can be regulated by innate immune system in pelvic microenvironment by their interaction with endometrial cells and immune cells. We conducted a series of studies in perspectives of pelvic inflammation that is triggered primarily by bacterial endotoxin (lipopolysaccharide, LPS) and is mediated by Toll-like receptor 4 (TLR4) and showed their involvement in the growth regulation of visible peritoneal endometriosis. Even with the careful eye of an expert surgeon, we may sometimes miss to detect peritoneal lesion within peritoneal cavity or deep into peritoneum. In such a case, random collection of normal peritoneum may carry the possibility to identify some hidden endometriotic lesions by microscopy and these lesions can be named as invisible endometriosis. Here, we discuss the color appearance of peritoneal lesions, role of innate immune system in visible endometriosis, and finally our recent findings on invisible microscopic endometriosis and their biological and clinical significance.