Menstrual Cycle PDF

CHAPTER 41 Normal Anatomy and Physiology of the Female Pelvis branches that perfuse the pelvic structures, including the urinary bladder, uterus, vagina, and rectum. The ovarian veins follow a slightly different course, as the left ovarian vein drains into the left renal vein, and the right ovarian...

CHAPTER 41 Normal Anatomy and Physiology of the Female Pelvis branches that perfuse the pelvic structures, including the urinary bladder, uterus, vagina, and rectum. The ovarian veins follow a slightly different course, as the left ovarian vein drains into the left renal vein, and the right ovarian vein drains directly into the inferior vena cava. Blood is supplied to the uterus by the uterine artery, which arises from the anterior branch of the internal iliac artery (Figure 41-17). From the internal iliac artery, the uterine artery crosses above and anterior to the ureter, extending medially in the base of the broad ligament to the uterus at the level of the cervix. The uterine artery is tortuous and spirals up the sides of the uterus within the broad ligament to the cornua, where it courses laterally to anastomose with the ovarian artery. The uterine artery gives off many branches that perforate the serosa and carry blood to the myometrium (Figure 41-18). These branches anastomose extensively anteriorly and posteriorly within the myometrium, forming arcuate (arclike) vessels that encircle the uterus. The arcuate vessels can often be identified sonographically as anechoic tubular structures in the outer third of the myometrium. Blood is supplied to the endometrium by the radial arteries, which “radiate” from the arcuate arteries within the myometrium. The radial arteries extend through the myometrium to the base of the endometrium, where straight and spiral arteries branch off the radial arteries to supply the zona basalis of the endometrium. The spiral arteries will lengthen during regeneration of the endometrium after menses to traverse the endometrium and supply the zona functionalis. Blood from the spiral arteries is shed during menses. The pelvic vessels supply blood to the functional layer of the endometrium. Internal iliac artery Tubal branch of uterine artery Ovarian branch of uterine artery 1061 2 3 1 4 5 6 18 19 15 17 13 14 12 7 16 11 9 10 8 FIGURE 41-18 ​Female pelvic vessels and viscera (seen on the right side in a sagittal section) after removal of most of the peritoneum. 1, Ovarian vessels; 2, external iliac artery; 3, external iliac vein; 4, ureter; 5, internal iliac vessels and branches; 6, piriformis; 7, rectum; 8, anus; 9, perineal body; 10, labium majora; 11, labium minora; 12, clitoris; 13, pubic symphysis; 14, urethra; 15, bladder; 16, vagina; 17, cervix of uterus; 18, left uterine artery; 19, body of uterus. PHYSIOLOGY The Menstrual Cycle A female’s reproductive years begin around 11 to 13 years of age at the onset of menses (menstruation) and end around age 50, when menses ceases. The average menstrual cycle is approximately 28 days in length, beginning with the first day of menstrual bleeding (Box 41-17). The length of the menstrual cycle can, however, vary considerably from one woman to another. BOX 41-17 The Menstrual Cycle Menstruation • Days 1–14 Cervical branch of uterine artery Ureter Infundibulopelvic ligament Uterine artery Vaginal artery Azygos arteries Internal pudendal artery FIGURE 41-17 ​Blood is supplied to the uterus and vagina by the uterine artery (arising from the internal iliac artery) and the vaginal artery (arising from the uterine artery). The ovaries receive blood from branches of the uterine artery and from the ovarian arteries arising from the abdominal aorta. Proliferative Phase • Days 5–14 • Corresponds to the follicular phase of ovarian cycle • Thin endometrium • Estrogen level increases as ovarian follicles develop • Increasing estrogen levels cause uterine lining to regenerate and thicken • Ovulation occurs on day 14 Secretory Phase • Days 15–28 • Corresponds to the luteal phase of ovarian cycle • Ruptured follicle becomes corpus luteum • Corpus luteum secretes progesterone • Endometrium thickens • If no pregnancy, estrogen and progesterone decrease 1062 CHAPTER 41 Normal Anatomy and Physiology of the Female Pelvis Menstrual status is described using the terms premenarche, menarche, and menopause. Premenarche is the physiologic status of prepuberty, the time before the onset of menses. Menarche is the state after reaching puberty in which menses occurs normally every 28 days. Menopause refers to the cessation of menses. The menstrual cycle is regulated by the hypothalamus and is dependent on the cyclic release of estrogen and progesterone from the ovaries. Follicular Development and Ovulation During the menarcheal years, an ovum is released once a month by one of the two ovaries. This process is known as ovulation. Ovulation normally occurs midcycle on about day 14 of a 28-day cycle. It is speculated that ovum release alternates between the two ovaries: one month from the right, the next month from the left. All ova begin development during embryonic life and remain in suspended animation within a preantral follicle as an immature oocyte until the onset of menarche. Each female ovary contains approximately 200,000 oocytes at the time of birth. Some of these oocytes will mature and be released from the ovaries during ovulation, whereas others will degenerate. The process of ovulation is regulated by the hypothalamus within the brain. When a girl reaches puberty, the hypothalamus begins the pulsatile release of the gonadotropin-releasing Ovulation Corpus luteum Endometrium Menstruation Menstruation Developing follicle hormones (GnRHs), which stimulate the anterior pituitary gland to secrete varying levels of gonadotropins (primarily follicle-stimulating hormone [FSH] and luteinizing hormone [LH]). Secretion of FSH by the anterior pituitary gland causes the ovarian follicles to develop during the first half of the menstrual cycle. This phase of the ovulatory cycle, known as the follicular phase, begins with the first day of menstrual bleeding and continues until ovulation on day 14 (Figure 41-19). As the ovarian follicles grow, they fill with fluid and secrete increasing amounts of estrogen. Although typically five to eight preantral follicles will begin to develop, only one usually reaches maturity each month. This mature follicle is known as a graafian follicle and typically measures 2 cm right before ovulation. As the estrogen level in the blood rises with follicle development, the pituitary gland is inhibited from further production of FSH and begins to secrete LH. The luteinizing hormone level will typically increase rapidly 24 to 36 hours before ovulation in a process known as the LH surge. This surge is often used as a predictor for timing ovulation for conception. LH level usually reaches its peak 10 to 12 hours before ovulation. It is the LH surge, accompanied by a smaller FSH surge, that triggers ovulation on about day 14. Ovulation is the explosive release of an ovum from the ruptured graafian follicle. Rupture of the follicle is associated with small amounts of fluid in the posterior cul-de-sac midcycle. Week 1 Week 2 Week 3 Week 4 FIGURE 41-19 ​The average menstrual cycle is approximately 28 days, beginning with the first day of bleeding. As the menstrual lining is shed, the pituitary gland begins to secrete follicle-stimulating hormone (FSH), which causes five to eight preantral ovarian follicles to develop. As the ovarian follicles grow, they fill with fluid and secrete increasing amounts of estrogen. This estrogen stimulates the superficial layer of the endometrium to regenerate and grow. As the estrogen level in the blood rises, the pituitary gland is inhibited from further production of FSH and begins to secrete luteinizing hormone (LH). The LH surges 24 to 36 hours before ovulation and is accompanied by a smaller FSH surge that triggers ovulation on about day 14. Ovulation occurs as the follicle ruptures, releasing the mature ovum. After ovulation, the cells lining the ruptured ovarian follicle begin to multiply and create the corpus luteum. The corpus luteum immediately begins to secrete progesterone. Progesterone causes the spiral arteries and endometrial glands to enlarge as the endometrium prepares​ for implantation should conception occur. Without conception, the corpus luteum degenerates 9 to 11 days after ovulation, causing progesterone levels to decline. Declining progesterone levels cause the spiral arterioles to constrict, resulting in decreasing blood flow to the endometrium with ischemia and shedding of the zona functionalis. As menstruation occurs, the menstrual cycle begins again. CHAPTER 41 Normal Anatomy and Physiology of the Female Pelvis Some women can tell when they are ovulating because at midcycle they have pain, typically a dull ache on either side of the lower abdomen lasting a few hours. The term mittelschmerz, from the German word meaning “middle pain,” is often used to describe this sensation. After ovulation, the ovary enters the luteal phase. This phase begins with ovulation and is about 14 days in length. It is interesting to note that the luteal phase does not usually vary in length. When a menstrual cycle is shorter or longer than 28 days, it is the follicular phase that is altered. Menstruation almost always occurs 14 days after ovulation. During the luteal phase, the cells in the lining of the ruptured ovarian follicle begin to multiply and create the corpus luteum, or yellow body. This process, known as luteinization, is stimulated by the LH surge. The corpus luteum immediately begins to secrete progesterone. Nine to 11 days after ovulation, the corpus luteum degenerates, causing progesterone levels to decline. As progesterone levels decline, menstruation occurs and the cycle begins again. Should conception and implantation occur, the human chorionic gonadotropin (hCG) produced by the zygote causes the corpus luteum to persist, and it will continue to secrete progesterone for 3 more months until the placenta takes over. Box 41-17 summarizes the phases of the menstrual cycle. Endometrial Changes Varying levels of estrogen and progesterone throughout the course of the menstrual cycle induce characteristic changes in the endometrium. These changes correlate with ovulatory cycles of the ovary. The typical endometrial cycle is identified and described in three phases, beginning with the menstrual phase (see Figure 41-19). The menstrual phase lasts approximately 1 to 5 days and begins with declining progesterone levels, causing the spiral arterioles to constrict. This causes decreased blood flow to the endometrium, resulting in ischemia and shedding of the zona functionalis. These first 5 days coincide with the follicular phase of the ovarian cycle. As the follicles produce estrogen, the estrogen stimulates the superficial layer of the endometrium to regenerate and grow. This phase of endometrial regeneration, called the proliferative phase, will last until luteinization of the graafian follicle around ovulation. With ovulation and luteinization of the graafian follicle, the progesterone secreted by the ovary causes the spiral arteries and endometrial glands to enlarge. This will prepare the endometrium for implantation, should conception occur. The endometrial phase after ovulation, referred to as the secretory phase, extends from approximately day 15 to the onset of menses (day 28). The secretory phase of the endometrial cycle corresponds to the luteal phase of the ovarian cycle. The sonographic appearance of the endometrium changes dramatically among the three phases of the endometrial cycle and should be correlated with the patient’s menstrual status (Figure 41-20). During menses, it is not uncommon to see varying levels of fluid and debris within the uterine cavity; likewise, the thickness of the endometrium will decrease with menstruation, becoming a thin echogenic line during the early proliferative phase. As regeneration of the endometrium 1063 Blood Luteal endometrium Myometrium Single line late menstrual endometrium 1 Three line proliferative phase 2 3 Thickened endometrium of late proliferative phase Thick secretory endometrium Vagina Posterior acoustic enhancement FIGURE 41-20 ​Cyclic changes in the endometrium. The menstrual cycle begins with approximately 5 days of bleeding. During menses, varying levels of fluid and debris may be seen within the uterine cavity. The thickness of the endometrium decreases with menstruation, becoming a thin echogenic line during the early proliferative phase. As regeneration ensues, the endometrium thickens and appears hypoechoic with a “three-line” sign. The outer echogenic line surrounding the hypoechoic functionalis represents the zona basalis, and the central echogenic line represents the uterine cavity. As ovulation nears, the endometrium becomes isoechoic with the myometrium. The secretory phase occurs after ovulation, when the endometrium reaches its thickest dimension and becomes hyperechoic. occurs during the proliferative phase, the endometrium will thicken to an average of 4 to 8 mm in the proliferative phase, when measured as a double layer from anterior to posterior. The endometrium characteristically appears hypoechoic with the appearance of the “three-line” sign. The three echogenic lines seen in the proliferative endometrium represent the zona basalis anteriorly and posteriorly, with the central line representing the uterine cavity. Right before ovulation, the endometrium averages 6 to 10 mm and becomes isoechoic with the myometrium. After ovulation, during the secretory phase, the endometrium reaches its thickest dimension, averaging 7 to 14 mm, and becomes echogenic, blurring the “three-line” appearance. The endometrium in anovulatory patients (e.g., those on the birth control pill, postmenopausal patients) will usually appear as a thin, echogenic line. Postmenopausal patients who are not on hormone replacement therapy (HRT) should have an endometrial thickness of less than 5 mm. Postmenopausal patients on HRT or taking tamoxifen (a drug used as adjuvant palliative therapy to help 1064 CHAPTER 41 Normal Anatomy and Physiology of the Female Pelvis in the prevention of breast cancer) may demonstrate normal endometrial thicknesses of up to 8 mm. Abnormal Menstrual Cycles Several terms are used to describe abnormal menstrual cycles and should be familiar to the sonographer. The term menorrhagia is used to describe abnormally heavy or long periods and is often associated with uterine fibroids, intrauterine contraceptive devices (IUDs), or hormonal imbalances. Persistent menorrhagia can lead to anemia. The term oligomenorrhea describes abnormally short or light periods and is often associated with polycystic ovary syndrome (PCOS). Oligomenorrhea can also be caused by emotional and physical stress, chronic illnesses, tumors that secrete estrogen, poor nutrition and eating disorders (e.g., anorexia nervosa), and heavy exercise. Polymenorrhea is when the menstrual cycle occurs at intervals of less than 21 days. Many patients complain of dysmenorrhea or painful periods. Dysmenorrhea is often associated with endometriosis. The term amenorrhea refers to the absence of menstruation. Amenorrhea is considered primary when menarche is delayed beyond 18 years of age, and secondary when cessation of uterine bleeding occurs in women who have previously menstruated. Amenorrhea may be due to a congenital vaginal or cervical stenosis or may result from infection, trauma, ovarian dysfunction, or other endocrine disturbances that affect ovarian function, such as pituitary disease. PELVIC RECESSES AND BOWEL The peritoneal cavity contains two potential spaces formed by the caudal portion of the parietal peritoneum (Box 41-18). These potential spaces are sonographically significant in that fluid may accumulate or pathology may be present in these locations. The vesicouterine recess (pouch), or anterior culde-sac, is located anterior to the fundus of the uterus between the urinary bladder and the uterus, and the rectouterine recess (pouch), or posterior cul-de-sac, is located posterior to the uterus between the uterus and the rectum. The rectouterine pouch is often referred to as the pouch of Douglas and is normally the most inferior and most posterior region of the peritoneal cavity. One additional area that is sonographically significant is the retropubic space (also called the space of Retzius). It can be identified between the anterior bladder wall and the pubic symphysis. This space normally contains BO X 4 1 - 1 8 Pelvic Recesses • Vesicouterine pouch: anterior cul-de-sac; anterior to the fundus between the uterus and bladder • Rectouterine pouch: posterior cul-de-sac; posterior to the uterine body and cervix, between the uterus and rectum • Retropubic space: space of Retzius; between bladder and symphysis pubis subcutaneous fat, but a hematoma or abscess in this location may displace the urinary bladder posteriorly. It is normal to observe a small accumulation of free fluid throughout the menstrual cycle in the posterior cul-de-sac (see Figure 41-9). The greatest quantity of free fluid in the cul-de-sac normally occurs immediately after ovulation when the mature follicle ruptures. A small amount of fluid in the posterior cul-de-sac is considered normal; however, there is no sonographic means of confirming that the fluid is related to ovulation. Hemorrhage or infection within the fluid may be related to a ruptured cyst, ascites, a ruptured corpus luteum cyst, ectopic pregnancy, or pelvic inflammatory disease. Key Pearls • Many pelvic landmarks, ligaments, and muscular structures within the pelvis are important to know to differentiate normal reproductive organs from muscular and vascular structures. • A transabdominal approach requires a full urinary bladder for use as an acoustic window and typically necessitates the use of a 3.5- to 5-MHz transducer for adequate ​ penetration. • A transvaginal examination performed with an empty bladder allows the use of a higher-frequency transducer, typically 7.5 to 10 MHz. • The lower margin of the pelvic cavity, the pelvic floor, is formed by the levator ani and coccygeus muscles and is known as the pelvic diaphragm. • The muscles found within the true pelvis include the piriformis muscles, obturator internus muscles, and muscles of the pelvic diaphragm. • The pelvic diaphragm is formed by the levator ani and coccygeus muscles and makes up the floor of the true pelvis. • The vagina is a collapsed muscular tube that extends from the external genitalia to the cervix of the uterus. • The uterine cervix protrudes into the upper portion of the vaginal canal, forming four archlike recesses called fornices. • The uterus consists of a fundus, body, and cervix. • The uterine wall consists of three histologic layers: the ​ serosa or perimetrium, the myometrium, and the ​ endometrium. • The endometrium consists primarily of two layers: the superficial functional layer (zona functionalis) and the deep basal layer (zona basalis). • The uterus is supported in its midline position by paired broad ligaments, round ligaments, uterosacral ligaments, and cardinal ligaments. • The position of the uterus is variable. The average uterine position is considered to be anteverted and anteflexed. • In multiparous females, the entire uterus may tip backward rather than forward and is described as a retroverted position. • The uterine fundus or body may also curve backward on the cervix, and this position is described as retroflexed.