Ultrasound of the Ovary and Endometrium

THE MENSTRUAL CYCLE

The last menstrual period relates to the onset of menses; therefore, the first day of the menstrual cycle is said to occur on the first day of bleeding. The average menstrual cycle lasts 28 days, with ovulation typically occurring around day 14. However, some menstrual cycles may last only 25 days while others may last up to 45 days.

1 Days 1 through 5 of the menstrual cycle correlate with menses, at which time the endometrium is shed.

The first menstrual cycle is termed menarche. Menarche occurs at different ages and may be influenced by environment and diet.

However, if an individual does not experience menarche before age 16, she is said to have primary amenorrhea.

Ultrasound of the Ovary and Endometrium

Primary amenorrhea may be caused by congenital abnormalities or congenital obstructions, such as an imperforate hymen. Secondary amenorrhea may be associated with endocrinologic abnormalities or pregnancy.

Secondary amenorrhea that is not associated with pregnancy is characteristically diagnosed in the postmenarchal woman who has had at least 12 months without a menstrual cycle

THE PHYSIOLOGY OF THE OVARIAN CYCLE

The ovarian cycle consists of two phases: the follicular phase and the luteal phase.

The follicular phase of the ovarian cycle is considered to begin on day 1 and lasts until day 14, thus, in effect, ending with ovulation. During the follicular phase, the anterior pituitary gland secretes FSH, which initiates the follicular development of the ovary.

Ultrasound of the Ovary and Endometrium

Many follicles are produced by the ovary. While numerous follicles manifest, only one follicle will be maintained and become the graafian follicle or dominant follicle prior to ovulation.

This graafian follicle, which can grow as large as 2.7 cm, contains the developing oocyte (egg) within a region called the cumulus oophorus.

Ultrasound of the Ovary and Endometrium

Around day 14, LH, produced by the anterior pitu itary gland, stimulates ovulation, at which time the graafian follicle, which has grown to a size of 15 to 27 mm, ruptures and expels a small amount of fluid and the ovum into the peritoneum.

The ovum is picked up by the fimbria of the fallopian tube and is propelled through the tube, either to be fertilized, resorbed by the body, or passed with menstruation.

Ultrasound of the Ovary and Endometrium

The second phase of the ovarian cycle, days 15 to 28, is termed the luteal phase. After the graafian follicle ruptures, it is temporarily turned into an endocrine gland in the form of the corpus luteum.

The corpus luteum, while producing estrogen in small amounts, primarily produces progesterone to maintain the thickness of the endometrium and prepare the endometrium for the (conceivably) fertilized ovum. All the other follicles undergo atresia.

Ultrasound of the Ovary and Endometrium

While the corpus luteum depends on LH to be maintained, progesterone negatively inhibits the production of LH by the anterior pituitary gland, resulting in the regression of the corpus luteum.

The remaining structure of the corpus luteum is now termed the corpus albicans, which can often be seen sonographically as a small echogenic scar on the ovary.1

THE PHYSIOLOGY OF THE ENDOMETRIAL CYCLE

The endometrium has two basic layers. The innermost portion, the functional layer, is the layer that changes throughout the menstrual cycle. The functional layer provides an appropriate location for implantation to occur. The outermost portion, the basal layer, is only slightly altered during the menstrual cycle. It consists of dense, cellular stroma

Ultrasound of the Ovary and Endometrium

The endometrial cycle consists of two phases: the proliferative phase and the secretory phase. The proliferative phase occurs after menstruation and lasts until ovulation.

The endometrium is influenced by estrogen and progesterone, which are produced by the ovary.

During the first half of the menstrual cycle, the endometrium undergoes thickening as a result of estrogen stimulation.

Thus, proliferation of the endometrium, which is described as the multiplication of similar forms, occurs during the proliferative phase of the endometrial cycle, as the functional layer increases in thickness.

Ultrasound of the Ovary and Endometrium

The secretory phase of the endometrial cycle occurs after ovulation and is stimulated by progesterone. Progesterone maintains the thickness of the endometrium in preparation for implantation. Should fertilization not take place, menses begin on day 1 of the cycle, resulting from a lack of estrogen and proges terone.

Ultrasound of the Ovary and Endometrium

Conversely, if fertilization does occur, the en dometrial thickness is maintained by the continual production of progesterone by the corpus luteum of pregnancy

SONOGRAPHIC APPEARANCES OF THE ENDOMETRIUM

As the hormones produced by the ovary act upon the endometrium, the thickness of the endometrium varies. Consequently, the sonographic appearance of the endometrium changes Following menses, the endometrium appears as a thin, echogenic line

Ultrasound of the Ovary and Endometrium

Thus, the early proliferative endometrium appears echogenic and thin and typically measures 4 mm on day 4 and 8 mm on day 8 of the cycle.

During the late proliferative phase, or periovulatory phase, the endometrial layers display a stark contrast and can measure between 6 and 10 mm.

The outer echogenic basal layer surrounds the more hypoechoic functional layer, while the functional layer is separated by the echogenic endometrial stripe

This finding is referred to as the three-line sign. Following ovulation, the secretory endometrium is maintained by the

production of progesterone, as the endometrium becomes thickened and echogenic in appearance and measures between 7 and 14 mm

Ultrasound of the Ovary and Endometrium

The thickness mea surement of the endometrium obtained with sonogra phy should not include the adjacent hypoechoic myometrium and is considered accurate when the double-layer thickness measurement is performed. The double-layer thickness includes only the distance from basal layer to basal layer.

DISRUPTION OF THE MENSTRUAL CYCLE BY PREGNANCY

Fertilization typically occurs on day 15, with the union of the egg and sperm in the fallopian tube. The cells that surround the blastocyst, the syncytiotrophoblastic cells (trophoblastic cells), then begin to produce human chorionic gonadotropin (hCG).

The production of hCG maintains the corpus luteum.

Ultrasound of the Ovary and Endometrium

Thus hCG allows the corpus luteum to continue to produce progesterone, which in turn maintains the thickness of the endometrium so that implantation can take place and the pregnancy can continue to progress normally.

ENDOMETRIAL PATHOLOGY

Endometrial Atrophy In the postmenopausal patient, the endometrium often bleeds spontaneously secondary to atrophy.

As a result, the most common cause of PMB is endometrial atrophy.

The endometrium will appear thin and will not measure more than 5 mm .It may also contain some intracavitary fluid.

A thin endometrial stripe in the postmenopausal female typically does not war rant endometrial biopsy.

Endometrial Hyperplasia

Endometrial hyperplasia is a common cause of abnor mal vaginal bleeding, not only in the postmenopausal female but also in the reproductive years.

Endometrial hyperplasia results from the unopposed stimulation of estrogen on the endometrium.

Ultrasound of the Ovary and Endometrium

Secondary to continual estrogen stimulation, the endometrium may contain a small cystic area and appear diffusely echogenic on sonography.

Ultrasound of the Ovary and Endometrium

Endometrial hyperplasia may also be caused by polycystic ovary syndrome, obesity, tamoxifen therapy for breast cancer, or estrogen-producing ovarian tumors.

There seems to be an increased risk for one form of endometrial hyperplasia (atypical adenomatous hyperplasia) progressing into endometrial carcinoma more often in the postmenopausal woman.

Ultrasound of the Ovary and Endometrium

Endometrial Polyps Endometrial polyps are small nodules of hyperplastic endometrial tissue that may cause abnormal vaginal bleeding in both postmenopausal or perimenopausal woman. They have been linked with infertility during the reproductive period.

Ultrasound of the Ovary and Endometrium

Clinically, patients may present with menometrorrhagia and/or intermenstrual bleeding, or may even be asymptomatic. Endometrial polyps can have many different shapes including a broad base or can be pedunculated and, if large, may prolapse through the cervix

Endometrial Carcinoma

Endometrial carcinoma is the most common female genital tract malignancy, with PMB being the most common clinical presentation. Endometrial carcinoma is most often in the form of adenocarcinoma,

ANATOMY AND PHYSIOLOGY OF THE OVARY

The ovaries form in the upper abdomen and descend into the pelvis in utero. They are paired, oval-shaped, intraperitoneal organs that have a dual blood supply from both the ovarian artery and ovarian branches of the uterine arteries.

As endocrine glands, the ovaries are responsible for releasing estrogen and progesterone in varying amounts throughout the menstrual cycle.

Ultrasound of the Ovary and Endometrium

The ovary consists of an outer cortex and an inner medulla. The medulla contains the ovarian vasculature and lymphatics, while the cortex involves the mass of the ovary and is the site of oogenesis.

The ovaries are stimulated by follicle-stimulating hormone, released by the anterior pituitary gland, to develop multiple follicles during the first half of the menstrual cycle (follicular phase)

The cells surrounding the tiny follicles produce estrogen, which stimulates the endometrium to thicken.

Only one of these follicles will become the dominant follicle, or graafian follicle, prior to ovulation, while all other follicles will atrophy.

Ultrasound of the Ovary and Endometrium

The ovumis contained within the cumulus oophorus of the dominant follicle. The cumulus oophorus may be seen within the ovary during a sonographic examina tion, with the sonographic appearance resembling that of a daughter cyst.

Ultrasound of the Ovary and Endometrium

At approximately day 14 of the menstrual cycle, ovulation occurs, as the dominant follicle ruptures, releasing the mature ovum and a small amount of follicular fluid into the peritoneal cavity.

Mittelschmerz, which means middle pain, describes pain at the time of ovulation, typically on the side of the dominant follicle.

Ultrasound of the Ovary and Endometrium

The fluid from the ruptured follicle most often will settle in the rectouterine pouch (pouch of Douglas), the most dependent portion of the peritoneal cavity. After the graafian follicle has ruptured, its structure is con verted into the corpus luteum.

Ultrasound of the Ovary and Endometrium

. During the second half of the menstrual cycle (luteal phase), the corpus luteum produces progesterone and, in small amounts, estrogen. If fertilization occurs, the corpus luteum is maintained and becomes the corpus luteum of pregnancy.

Ultrasound of the Ovary and Endometrium

If fertil ization does not occur, the corpus luteum regresses and becomes the corpus albicans. The ovarian cycle is fur ther discussed in Chapter 19.

Ultrasound of the Ovary and Endometrium

Sonographically, the normal ovary is homogenous with a medium-level to low-level echogenicity. Multiple follicles may be noted with sonography during the neonatal and prepubertal ages.

Also, follicles on the ovaries, of varying sizes, may be seen throughout the normal menstrual cycle during reproductive years

Ultrasound of the Ovary and Endometrium

Ovarian volume can be determined sonographically by utilizing the following formula: volume length width height 0.5233. It is important to note that the postmenopausal ovaries atrophy and are often difficult to locate sonographically.

PATHOLOGY OF THE OVARY

Benign Ovarian Disease

Follicular Cysts

Should the graafian follicle fail to ovulate, it could continue to enlarge and result in a follicular cyst. Follicular cysts range in size from 3 to 8 cm; however, larger cysts have been documented. Their sonographic appearance is most often described as anechoic, thin walled, and unilocular

Ultrasound of the Ovary and Endometrium

Most follicular cysts regress and is responsible for producing progesterone, thereby maintaining the endometrium during an early pregnancy in preparation for implantation. The corpus luteum will normally regress if fertilization does not occur but may rarely be maintained and continue to enlarge.

Ultrasound of the Ovary and Endometrium

A follicular cyst that contains blood is referred to as a hemorrhagic cyst, and it most often appears complex or completely echogenic depending on the hemorrhagic component present and the stage of lysis

Corpus Luteum Cysts

(Corpus Luteal Cysts) The corpus luteum cyst is a physiologic cyst that develops after ovulation has occurred.

The corpus luteum is formed as a result of the rupture of the graafian follicle and is responsible for producing progesterone, thereby maintaining the endometrium during an early pregnancy in preparation for implantation.

Ultrasound of the Ovary and Endometrium

Corpus luteum cysts may reach sizes up to 8 cm, with resolution of the cyst taking place within 1 to 2 months in menstruating patients. Pain is associated with enlargement of the cyst, hemorrhage, and rupture. If the cyst is large, it can lead to ovarian torsion.

Ultrasound of the Ovary and Endometrium

In the presence of a pregnancy and human chorionic gonadotropin (hCG), the corpus luteum is also preserved. In this case, the cyst may be referred to as the corpus luteum of pregnancy.

These cysts are considered the most common pelvic masses seen during a first-trimester sonographic examination.

Ultrasound of the Ovary and Endometrium

They may even reach sizes of up to 10 cm, although most often they resolve by 16 weeks gestation and do not exceed 3 cm.

They tend to appear as simple cysts, although they may also have thick walls and may be difficult to differentiate from other solid and cystic adnexal masses

Ultrasound of the Ovary and Endometrium

Patients with large corpus luteum cysts may present with pelvic pain if the cyst has ruptured or if hemorrhage within the cyst has occurred. Often, complex or thick-walled corpus luteum cysts resemble an ectopic pregnancy,

Ultrasound of the Ovary and Endometrium

Corpus luteum. The range of sonographic appearances of the corpus luteum includes that of a thin-walled unilocular cyst (A), a thick-walled cyst (B), a complex cyst with septations (C), and structure that contains diffuse internal echoes (D)

Cystic Teratoma (Dermoid)

The most common benign ovarian tumor is the cystic teratoma, or dermoid cyst. Dermoids result from the retention of an unfertilized ovum that differentiates into the three germ cell layers.

Therefore, these germ cell tumors are composed of ectoderm, mesoderm, and endo derm.

Endometrioma (Chocolate Cyst)

An endometrioma is a benign, blood-containing tumor that forms from the implantation of ectopic endometrial tissue, a condition known as endometriosis. This ectopic endometrial tissue is functional.

Ultrasound of the Ovary and Endometrium

causing it to hemorrhage. Hemorrhage from endometriosis forms into focal areas of bloody tumors known as endometriomas. These lesions have been termed “chocolate cysts” be cause of their blood content. Therefore, the hormones of menstruation act on this tissue just as if it were located within the uterus,

Ultrasound of the Ovary and Endometrium

Endometriomas can be located anywhere outside of the endometrial cavity, including on any other pelvic organ, such as the bladder and bowel, but are more commonly found on the ovary. Most often these masses are multiple and seen more often in the repro ductive years.

Ultrasound of the Ovary and Endometrium

The cause of endometriosis is still unknown; how ever, several hypotheses exist. One theory suggests that implantation of this ectopic tissue is a result of en dometrial tissue being passed through the fallopian tubes during menstruation,

Ultrasound of the Ovary and Endometrium

while another proposes that scaring from surgery, such as a cesarean section, leads to endometriosis and the subsequent development of endometriomas.