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Eyes wide shut: the illusory tale of 'occult' microscopic endometriosis.

The visual appearance of endometriosis is important because every intellectual and therapeutic process begins with a surgeon identifying disease. Inaccurate identification of disease can introduce selection bias at a firstorder level and confound all conclusions, leading to inaccurate concepts of epidemiology, natural history, disease origin and treatment. David B. Redwine, M.D. (1990) In this issue of Human Reproduction, Khan et al. (2013) revive the debate on the existence and clinical relevance of invisible microscopic endometriosis (IME)—now renamed by them as occult microscopic endometriosis (OME). They report new evidence for immunoreactive microscopic endometriosis in visually normal peritoneum during laparoscopy, as well as an incidence of OME, which is higher than that reported in previous laparoscopic studies of visually normal peritoneum (Redwine, 1988a; Redwine and Yocom, 1990; Nezhat et al., 1991). It is important to outline the concepts central to any discussion on OME— namely, the definition of OME, the criteria and methodology employed to identify visually normal peritoneum, and the definition of endometriosis applied in judging the presence or absence of disease in the biopsied tissue. In defining OME an important distinction must be drawn between failure to recognize visually detectable areas of disease and the presence of microscopic disease that truly cannot be visually detected by the laparoscope. Recognition of the complete morphological repertoire of endometriosis, in all its protean presentations, and the utilization of welldefined criteria and methodology to detect all areas of visually abnormal peritoneum are paramount. Doing so ensures that contributions to the IME/OME literature are internally valid, reproducible and can be critically evaluated within the context of the existing body of research. Moreover, consensus is needed as to the histological definition of endometriosis. If different authors apply ever-broader definitions of disease, there is a risk of defining endometriosis into existence from any histologic appearance. The concept of OME is of importance not only in predicting the outcomes and clinical utility of the complete surgical excision of endometriosis but also has far-reaching implications regarding disease phenomenology, pathogenesis and prognosis as indicated in the historical quote introduced in this editorial (Redwine, 1990). How confused has the endometriosis literature become by virtue of incomplete identification of disease? Murphy et al. (1986) introduced the concept of OME in, reporting microscopic disease in visually normal peritoneum in 25% of a series of 20 patients undergoing laparotomy for endometriosis. This prevalence of OME remains to this day the highest rate ever reported. No formal criteria for normal peritoneum were used in that study, however, and the peritoneal surfaces were viewed at arm’s length and with the limited illumination attendant to laparotomy. Subsequent studies conducted via