Endometriosis is a common benign gynecologic disorder defined as the presence of endometrial glands and stroma outside of the normal location. First identified in the mid-19th century, endometriosis is most commonly found on the pelvic peritoneum but may also be found on the ovaries, rectovaginal septum, and ureter, and rarely in the bladder, pericardium, and pleura (Comiter, 2002; Giudice, 2004; Von Rokitansky, 1860). Endometriosis is a hormonally dependent disease and as a result is chiefly found in reproductive-aged women. Women with endometriosis may be asymptomatic, subfertile, or suffer varying degrees of pelvic pain. Endometrial tissue located within the myometrium is termed adenomyosis, or sometimes referred to as endometriosis in situ, and is discussed in greater detail in Chapter 9.
The incidence of endometriosis is difficult to quantify, as women with the disease are often asymptomatic, and imaging modalities have low sensitivities for diagnosis. The primary method of diagnosis is laparoscopy, with or without biopsy for histologic diagnosis (Kennedy, 2005; Marchino, 2005b). Using this standard, investigators have reported the annual incidence of surgically diagnosed endometriosis to be 1.6 cases per 1000 women aged between 15 and 49 years (Houston, 1987). In asymptomatic women, the prevalence of endometriosis ranges from 2 to 22 percent, depending on the population studied (Eskenazi, 1997; Mahmood, 1991; Moen, 1997). However, because of its link with infertility and pelvic pain, endometriosis is notably more prevalent in subpopulations of women with these complaints. In infertile women, the prevalence has been reported to be between 20 and 50 percent and in those with pelvic pain, between 40 and 50 percent (Balasch, 1996; Eskenazi, 2001; Meuleman, 2009).
Although the definitive cause of endometriosis remains unknown, several theories with supporting evidence have been described.
The earliest and most widely accepted theory describes retrograde menstruation through the fallopian tubes and subsequent dissemination of endometrial tissue within the peritoneal cavity (Sampson, 1927). Refluxed endometrial fragments adhere to and invade the peritoneal mesothelium and develop a blood supply, which leads to continued implant survival and growth (Giudice, 2004).
First proposed in the 1920s, this theory has gained support with the findings of greater volumes of refluxed blood and endometrial tissue in the pelves of women with endometriosis (Halme, 1984). Uterine hyperperistalsis and dysperistalsis have been noted in women with endometriosis and resulted in subsequent increased endometrial reflux (Leyendecker, 2004). Additionally, D'Hooghe (1997) demonstrated that surgical obliteration of the cervical outflow tract in baboons leads to the induction of endometriosis. Women with amenorrhea due to outflow tract obstruction similarly have a high incidence of endometriosis, which is often relieved by correction of the obstruction (Sanfilippo, 1986).
Lymphatic or Vascular Spread
Evidence also supports the ...