Ultrasonography shows no specific pattern for pelvic endometriosis, but is often helpful in diagnosing persistent nonfunctioning ovarian cysts that may represent endometriomas. Although some specialists seem to think that they can diagnose an endometrioma with certainty using ultrasound, there are abundant scientific reports confirming the nonspecific nature of the ultrasound for this purpose. Endometriotic lesions depend upon stimulation by estrogens. Endometriosis discovered after menopause is almost always associated with hormone replacement medication containing estrogens. The incidence of endometriosis is not known, since the only reliable way of determining its presence is through surgery or at autopsy.
Surgical incidence is biased by the selection process bringing the patient to the operating room.
No large cadaver study examining autopsy specimens for endometriosis has reported data that has been widely accepted. There are three main theories for the mechanism causing endometriosis. Each theory has many supporters. It may be that each of these three may accurately describe one of several possible mechanisms. In the 1920s a physician named John Sampson devoted a great deal of time to the study of endometriosis and is widely credited with the initial suggestion that retrograde flow is the primary path for this tissue to grow in the pelvis.