Endometriosis By James H Liu, MD, Case Western Reserve University School of Medicine Reviewed / Revised Apr 2022 | Modified Sep 2022 View Patient Education Etiology and Pathophysiology Symptoms and Signs Diagnosis Treatment Key Points Topic Resources Stages of Endometriosis Drugs Used to Treat Endometriosis In endometriosis, functioning endometrial cells are implanted in the pelvis outside the uterine cavity.