The normal ovary is ellipsoid in shape and is variable in both location and orientation, depending upon the age and parity of the patient as well as the degree of bladder distention. In the nulliparous adult female, the ovaries are situated in the ovarian fossa (also known as the fossa of Waldeyer), which is adjacent to the lateral pelvic side wall and is bounded by the obliterated umbilical artery anteriorly, the ureter and internal iliac artery posteriorly and the external iliac vein superiorly. Ovarian volume is calculated by measuring the ovary in three dimensions (length, width, and depth) on two orthogonal planes and using the formula for the prolate ellipse (L × W × D/2).
In premenopausal women, the mean ovarian volume is 9.8 mL (with 5% and 95% confidence intervals of 2.5 and 21.9 mL), with the highest volumes found in the preovulatory phase and the lowest volumes in the luteal phase. The normal ovary in women of reproductive age has a variable appearance over the course of the menstrual cycle. Developing and immature follicles can be seen throughout the entire menstrual cycle and appear as anechoic, unilocular, sharply marginated cysts, measuring from 2 to 9 mm. By days 8 to 12 of the menstrual cycle, one or more dominant follicles will grow to a diameter of approximately 20 to 25 mm and then rupture at ovulation, releasing the oocyte.Up to 80% of patients have a second nondominant follicle that becomes almost as large as the dominant follicle. The preovulatory dominant follicle may have a slightly complex appearance, with the oocyte and its supporting structures appearing as a ring-like structure within the follicle (the cumulus oophorus). Following ovulation, the corpus luteum evolves from the remnant of the mature follicle through a process of cellular hypertrophy and increased vascularization of the cyst wall. Therefore, a corpus luteum is typically visible in the secretory phase of the menstrual cycle and in the first few weeks of early pregnancy.
On sonography, corpus luteum typically has a relatively thick, homogeneously echogenic wall, the inner margin of which may be slightly irregular with a crenulated appearance. Internal echoes are common, reflecting variable amounts of internal hemorrhage that occurred at the time of ovulation and occasionally a corpus luteum may be filled with homogeneous low level echoes mimicking a solid mass. There is usually evidence of enhanced through transmission because of the fluid content and there will be no central vascularity.
Typically the corpus luteum is under 3.0 cm in maximal dimension but rarely it may become larger.If pregnancy does not occur, the corpus luteum gradually involute and atrophies to become the corpus albicans, which is typically not Sonographically identifiable.
The uterus consists of two major parts: the body (or corpus) and the cervix. The corpus is predominantly muscular, whereas the cervix is composed predominantly of collagenous and elastic tissue and has only 10% smooth muscle. The isthmus is a narrow portion or “waisting” of the uterus that corresponds to the approximate position of the internal osand demarcates the boundary between the lower uterine segment of the corpus and the cervix. The anterior surface of the corpus is almost flat, whereas the posterior surface is convex. The fallopian tubes emerge from the cone-shaped cornua of the uterus, situated at the junction between the superior and lateral uterine margins.
The fundus of the uterus is the superior portion of the uterus above the level of the insertion of the fallopian tubes. The overall uterine length is measured on a midline sagittal image from the tip of the serosal surface of the fundus to the distal aspect of the cervix (i.e., the external os). The AP dimension of the uterus is measured on the same sagittal image from its outer anterior to outer posterior wall, in a plane perpendicular to the longitudinal axis. The maximum width is measured outer wall to outer wall on the transverse or coronal view.Uterine size varies with age as well as with parity in the reproductive age patient. The uterus measures approximately 6 to 8.5 cm in length in nulliparous women and 8 to 10.5 cm in multiparous women.25-27 The AP diameter ranges from 2 to 4 cm in nulliparas and 3 to 5 cm in multiparas, whereas the width of the corpus measures approximately 3 to 5 cm in nulliparous women and 4 to 6 cm in multiparas.
The endometrium is composed of a superficial layer (zona functionalis) and a deeper basalis layer. The thickness and sonographic appearance of the endometrium change cyclically during the menstrual cycle. In the menstrual and very early proliferative phase, the endometrium is thin, usually under 4 mm, and appears brightly echogenic and homogeneous. Throughout the mid to late proliferative phase of the cycle (days 5 to 14) the functionalis layer of the endometrium increases in thickness under the influence of estrogen and becomes more hypoechoic compared to the basalis layer, such that the endometrium develops a trilaminar or striated appearance, typically measuring 12 to 13 mm (normal range 10-16 mm) at ovulation.
During the secretory phase (days 15 to 28), the functional layer becomes thickened, soft, and edematous under theinfluence of progesterone. A glycogen-rich fluid is secreted by the glandular epithelium, and the spiral arteries become tortuous. The resultant effect is that the functional layer increases in echogenicity to become once again isoechoic to the basalis layer. At the end of the secretory stage, the endometrium may measure up to 16 to 18 mm in thickness and is homogeneous in echotexture.
Endometrial thickness is best assessed on TVS, and by convention is reported as the sum of the measurement of both the anterior and posterior layers of the endometrium at the thickest segment on a midline longitudinal image. It is critical that the measurement be made on a midline sagittal image, as imaging obliquely or too close to the uterine cornua will result in an overestimation of endometrial thickness. If the endometrium can be shown to be continuous with the endocervical canal, the sonographer can be certain that the imaging plane is midline.
The central thin echogenic line represents the interface between the two layers of the endometrium and should be continuous. Disruption of the central echogenic white line or heterogeneity of the endometrium may indicate an underlying intracavitary lesion, such as a polyp, myoma, or adhesion. The subjacent hypoechoic subendometrial halo just peripheral to the endometrium represents the innermost layer of the myometrium and should not be included in endometrial measurement A small amount of hypoechoic fluid or mucus within the endometrial cavity may be a normal finding, but should not be included in the endometrial thickness measurement.
THE FALLOPIAN TUBE
The fallopian tubes are variable in length, measuring approximately 7 to 12 cm. Each tube is situated in the superior free margin of the broad ligament and is covered by peritoneum. The fallopian tube is narrowest in the interstitial or intramural portion as it travels through the muscular wall of the uterus to open into the cornual region of the endometrial cavity.
The interstitial portion of the fallopian tube measures approximately 1 cm in length and can be visualized with TVS in the superior right and left lateral corpus of the uterus as a fine, echogenic line arising from the angular, most lateral cephalad edge of the endometrial canal and running somewhat obliquely through the uterine wall toward the serosal surface.
UTERINE DIDELPHYS AND BICORNUATE UTERUS
Although often overlooked, adenomyosis is a common condition, reported in up to 70% of hysterectomy specimens. Adenomyosis is characterized by migration of endometrial glands and stroma from the stratum basale into the myometrium
MULTIPLE BRIGHT ECHOGENIC FOCI INDICATING ADENOMYOSIS
Leiomyomas (fibroids or myomas) are benign smooth muscle neoplasms with varying amounts of fibrous tissue and are the most common uterine neoplasm, reported in 20% to 30% of women over 30 years of age. Leiomyomas are more common in African-American women. Other risk factors include obesity, early age of onset of menstruation, and a diet rich in red meat.
There may be a genetic predisposition. These tumors are usually multiple, causing enlargement of the uterus with a lobular serosal contour unlike adenomyosis, which results in globular but smooth-contoured uterine enlargement. Leiomyomas most commonly present with a palpable pelvic mass, uterine enlargement, pelvic pain, anemia, and dysfunctional uterine bleeding. Symptoms are largely related to location and size. The vast majority of leiomyomas are intramural, submucosal (including intracavitary), or subserosal in location.
Chronic PID may result in obstruction of the ampullary segment of the fallopian tube, causing hydrosalpinx with fluid-filled dilatation of the fallopian tube. Although PID is the most common cause of hydrosalpinx, other causes include tubal ligation, hysterectomy without salpingo-oophorectomy, endometriosis, prior surgery, and malignancy. Hydrosalpinx may be a cause of pelvic pain and infertility. At sonography, a dilated fallopian tube in the absence of infection appears as a C-, U-, or S-shaped anechoic, avascular tubular structure, generally with a thin wall less than 5 mm thick.
Endometriosis is defined as the presence of endometrial glands and stroma in ectopic locations outside the uterus. This disorder is associated with a wide variety of symptoms including dysmenorrhea, dyspareunia, chronic pelvic pain, and dysfunctional uterine bleeding. Although pain is usually chronic, complications of endometriosis may result in a more acute presentation. Infertility is an important consequence of endometriosis, due to associated anatomic distortion of the pelvic structures and obstruction of the fallopian tubes. Endometriosis affects up to 10% of women of reproductive age, although in women with pelvic pain, infertility, or both, the prevalence is estimated to be as high as 35% to 50%. Because endometriosis is hormonally responsive, symptoms are often cyclic in nature, and there is repetitive hemorrhage into these lesions. The pathogenesis of endometriosis is complex and remains the subject of debate.Proposed theories include origin of implants from the uterine endometrium, possibly from lymphatic or hematogenous dissemination of endometrial cells or retrograde menstruation.The most common sites of endometriotic implantation include the surface of the ovary, uterine suspensory ligaments, uterus or fallopian tube, and the peritoneal surfaces of the pouch of Douglas.
CHOCOLATE CYST ON SCAN
Current treatment options for endometriosis include both medical (primarily hormonal) and surgical management. Diagnostic laparoscopy remains the reference standard for diagnosis and staging of endometriosis, although the role of imaging in endometriosis has continued to evolve. The ovaries are the most common sites of endometriosis and are frequently involved with multiple and bilateral lesions. The classic sonographic appearance of an endometrioma, often referred to as a chocolate cyst because of the presence of thick, dark, degenerated blood products from repetitive cyclic episodes of bleeding, is that of a homogeneous, hypoechoic lesion with low to medium level echoes and no internal vascularity. This has often been referred to as a “ground glass” appearance and is highly predictive of an endometrioma.
As with cysts elsewhere in the body, ovarian cysts with thin walls, anechoic internal contents, posterior acoustic enhancement, and no septations or solid components meet sonographic criteria for simple cysts. Follicular or corpus luteal cysts and serous cystadenomas may appear as simple cysts by sonographic criteria.
Fibrin strands and retracting clot are highly specific features of hemorrhagic ovarian cysts. The fibrin strands are often described as lacy, reticular, fishnet, cobweb, spider web, or sponge-like in appearance.
Mature Cystic Teratomas
Mature cystic teratomas of the ovary, also termed dermoids, account for up to 20% of ovarian neoplasms. These benign germ cell tumors are composed of at least two of the three germ cell layers (ectoderm,mesoderm, and endoderm). Dermoids are estimated to account for up to 20% of all ovarian tumors found in adult women and are bilateral in 15% to 25% of cases. Most dermoids are asymptomatic and are incidentally detected. However, dermoids may present with symptoms related to large size resulting in compression of adjacent structures.
Torsion or rupture of a dermoid may cause significant pain. Severalcharacteristic sonographic appearances have been described, including focal or diffuse hyperechoic component; areas of acoustic shadowing, also known as the “tip of the iceberg” sign; and echogenic lines and dots, also referred to as dermoid “mesh” or “dot-dash” sign.Any combination of these classic sonographic features allows a confident diagnosis of a dermoid. The hyperechoic component, termed a Rokitansky nodule, typically corresponds to mixed hair and sebaceous material or occasionally to calcification, sometimes related to a bone or tooth.
Patients with PCOS often present with the clinical triad of amenorrhea, hirsutism, and obesity, although clinical presentation is variable. Patients with PCOS are at increased risk of anovulation and thus infertility.35 In 2003, the Rotterdam Consensus workshop published what was considered the standard sonographic diagnostic criteria for PCOS: 12 or more 2- to 9-mm follicles in each ovary and/or increased ovarian volume measuring more than 10 mL.
ROLE OF ULTRASOUND IN IVF
Ultrasound plays a critical role in the monitoring of folliculogenesis that occurs during ovulation induction and of controlled ovarian stimulation from parenterally administered gonadotropins or orally administered clomiphene citrate. The choice of treatment is made by a reproductive endocrinology specialist, based upon the most likely cause of the infertility. In general, patients with anovulatory cycles, such as those with PCOS, are treated with clomiphene citrate, whereas patients with hypothalamic pituitary failure, diminished ovarian reserve, or failing ovaries, as well as women with unexplained infertility, might be treated with gonadotropins. Ovarian stimulation is initiated during the first few days of a normal menstrual cycle. Under the influence of stimulating hormones, multiple enlarging follicles can be seen, rather than the typical single dominant follicle created during a natural menstrual cycle.
Patients with infertility who undergo assisted reproduction are at risk for several possible complications, including ovarian hyperstimulation syndrome (OHSS), hemorrhage, or infection.62,63 OHSS is an iatrogenic process that occurs in patients who have undergone ovulation induction with gonadotropins, typically after the administration of hCG. OHSS is estimated to occur in 2% to 10% of patients undergoing assisted reproduction,63-65 and this complication is more likely to occur in those with higher numbers of developing follicles or high levels of estradiol.
OHSS can occur during the luteal phase of the cycle, prior to a positive pregnancy test, or in the early stages of pregnancy The imaging findings of OHSS include marked enlargement of the ovaries (>10 cm in diameter) with numerous follicles and associated free intraperitoneal fluid because of third spacing. Pleural effusions can be seen in severely affected patients (Fig. 32-21A through D). The ovaries typically contain multiple complex cysts, representing recently instrumented follicles with hemorrhage. Patients may present with abdominal distention, weight gain, and hemoconcentration from third spacing of fluid.
Infertility continues to be an important health care issue, and the role of sonography in the care of an infertile woman is clearly established. From baseline evaluation to assess for structural abnormality (such as endometrial mass, uterine anomaly, or hydrosalpinx) or low antral follicular count, to monitoring of folliculogenesis, guidance for oocyte retrieval and detection of possible post treatment complications, sonography, in particular transvaginal sonography, plays an essential role in the diagnosis and clinical management of these patients.