Causes of Bleeding

Abnormal uterine bleeding (AUB) is one of the most common reasons patients present to the gynecologist [1]. Fibroids are a major cause of abnormal uterine bleeding within the PALM-COEIN classification system, with “L” standing for leiomyoma [2]. Fibroids occur in multiple locations throughout the uterus (Figure 7.1), and heavy menstrual bleeding due to fibroids can result in severe anemia and decreased quality of life [3]. Despite a century of research on fibroids, there is no clear consensus on the mechanisms underlying uterine bleeding secondary to fibroids. This chapter will summarize the evolving hypotheses regarding the pathophysiology of fibroid-related bleeding. This chapter summarizes the evolving hypotheses regarding the pathophysiology of fibroid-related bleeding. Historically, it was thought that fibroids exert mechanical forces on the uterus, causing bleeding via three main structural mechanisms: endometrial thinning/hyperplasia, venule ectasia and contractile defects. Contemporary data support that neither the size nor the location of fibroids are consistently associated with symptoms of bleeding, which would be expected if mechanical forces exerted by fibroids were the entire explanation for pathogenesis of heavy menstrual bleeding. Since fibroids are known to be hyperresponsive to estrogen and have increased numbers of both estrogen and progesterone receptors, activation of fibroid hormone receptors may be key to the dysregulation of angiogenesis that has been associated with abnormal uterine bleeding. Therefore, blood loss related to fibroids may stem from alterations in uterine angiogenesis and perivascular capsule hemorrhage rather than bleeding within the fibroid itself.