Endometriosis is classically defined as the presence of endometrial glands and stroma in ectopic locations. Affecting from 6% to 10% of reproductive-aged women, endometriosis may result in dysmenorrhea, dyspareunia, chronic pelvic pain, and/or subfertility. The prevalence of this condition in women experiencing pain, infertility, or both is as high as 50%. Endometriosis is a debilitating condition, posing quality-of-life issues for the individual patient. The disorder represents a major cause of gynecologic hospitalization in the United States, estimated to have exceeded $3 billion in inpatient health care costs in 2004 alone. The significant individual and public health concerns associated with endometriosis underscore the importance of understanding its pathogenesis. The first recorded description of pathology consistent with endometriosis was provided by Shroen in 1690. Despite the passage of time and extensive investigation, the exact pathogenesis of this enigmatic disorder remains unknown.

THEORIES REGARDING PATHOGENESIS

Numerous theories detailing the development of endometriosis have been described. For purposes of review, these theories can generally be classified into those that propose that implants arise from tissues other than the endometrium and those that propose that implants arise from uterine endometrium (Table 10.1.1).

Nonendometrial Origin

Metaplasia of coelomic epithelium represents a distinct pathogenic mechanism for the establishment of endometriotic implants.