gynecology and obstetrics
Amenorrhea
Pathophysiology of Amenorrhea
Normally, the hypothalamus generates pulses of gonadotropin-releasing hormone (GnRH). GnRH stimulates the pituitary to produce gonadotropins (follicle-stimulating hormone [FSH] and luteinizing hormone [LH]—see figure Normal Menstrual Cycle ), which are released into the bloodstream. Gonadotropins stimulate the ovaries to produce Follicle-stimulating hormoneactivates aromatase in ovarian granulosa cells that surround the developing oocytes to convert androgens toestradiol. Luteinizing hormonesurges during the menstrual cycle; this surge promotes maturation of the dominant oocyte, release of the oocyte, and formation of the corpus luteum (which producesprogesterone). Estrogenstimulates the endometrium, causing it to proliferate. Progesteronechanges the endometrium into a secretory structure and prepares it for egg implantation (endometrial decidualization). production decrease, and the endometrium breaks down and is sloughed during menses. Menstrual Cycle occurs 14 days after ovulation in typical cycles. This figure shows the idealized cyclic changes in pituitary gonadotropins,estradiol(E2),progesterone(P), and uterine endometrium during the normal menstrual cycle. When part of this system malfunctions, ovulatory dysfunction occurs; the cycle of gonadotropin-stimulatedestrogenproduction and cyclic endometrial changes is disrupted, resulting in anovulation, and menstrual flow may not occur. Ovulatory dysfunction is the most common cause of amenorrhea, particularly secondary amenorrhea. However, amenorrhea can occur when ovulation is normal, as occurs when genital anatomic abnormalities (eg, congenital anomalies causing outflow obstruction, intrauterine adhesions [Asherman syndrome]) prevent normal menstrual flow despite normal hormonal stimulation. 