Endometriosis is a common benign disorder defined as the presence of endometrial glands and stroma outside of the normal location. Implants of endometriosis are most often found on the pelvic peritoneum, but other frequent sites include the ovaries and uterosacral ligaments. Endometrial tissue located within the myometrium is termed adenomyosis and discussed in Chapter 9. Women with endometriosis may be asymptomatic, subfertile, or suffer varying degrees of pelvic pain. This is an estrogen-dependent disease and thus lends itself to hormone-based treatment. However, in those with disease refractory to medical management, surgery may be required.
The incidence of endometriosis is difficult to quantify, as women with the disease are often asymptomatic. Moreover, imaging modalities have low sensitivities for small implants (Wall, 2015). The primary method of diagnosis is laparoscopy, with or without biopsy for histologic diagnosis (Dunselman, 2014). Using this standard, the annual incidence of surgically diagnosed endometriosis was 1.6 cases per 1000 women aged between 15 and 49 years (Houston, 1987). In asymptomatic women, the prevalence of endometriosis ranges from 6 to 11 percent, depending on the population studied and mode of diagnosis (Buck Louis, 2011; Mahmood, 1991). However, because of its link with infertility and pelvic pain, endometriosis is notably more prevalent in subpopulations of women with these complaints. From studies, the prevalence lies between 20 to 50 percent in infertile women, and in those with pelvic pain, it ranges from 40 to 50 percent (Balasch, 1996; Eskenazi, 2001; Meuleman, 2009). In adolescents, Janssen and coworkers (2013) reported that nearly two thirds of adolescents undergoing diagnostic laparoscopy for pelvic pain had evidence of endometriosis.
Previously, white women were thought to be disproportionately affected. More recent studies have provided variable results. Some show greater rates for whites and Asians, whereas others have found no statistically significant differences in endometriosis prevalence among any racial or ethnic groups (Jacoby, 2010). Of other patient characteristics, lower body mass appears to positively correlate with endometriosis risk (Peterson, 2013; Shah, 2013).
The definitive cause of endometriosis remains unknown, but theories have been proposed. A more favored one describes retrograde menstruation through the fallopian tubes (Sampson, 1927). These refluxed endometrial fragments invade the peritoneal mesothelium and develop a blood supply for implant survival and growth. Supporting data include a report that surgical obliteration of the outflow tract in baboons induces endometriosis (D’Hooghe, 1997). In correlation, women with outflow tract obstruction also have a high incidence of endometriosis, which often resolves following obstruction relief (Sanfilippo, 1986; Williams, 2014). Importantly however, most women have retrograde menstruation (Halme, 1984). Thus, other factors, such as immunologic and angiogenic components, likely aid implant persistence.