US examination of the pelvis is routinely performed both transabdominally with a full bladder and transvaginally with the bladder empty. Additional examination techniques include the translabial imaging and sonohysterography.

Examination is often begun using the transabdominal (TA) approach. The patient is asked to fill her bladder by drinking several glasses of fluid and by not urinating for at least 1 hour prior to examination. The patient lies supine on the examination table. A 3.5-5.0-MHz sector transducer is placed on the lower abdomen just above the symphysis pubis and the pelvic organs are examined through the window of the distended bladder. Bladder filling is ideal when the bladder dome is just above the uterine fundus. Overdistention compresses the normal anatomy and displaces masses and fluid out of the pelvis. Underdistention limits visualization. Images are obtained in sagittal and transverse planes. To optimally image the uterus, the transducer is aligned with the long axis of the uterus, which is often angled right or left from the midline cervix. The ovaries and adnexa are often best seen by sliding the transducer to the contralateral side and angling back toward the ovary of interest. Measurements are obtained of the uterus, ovaries, and any masses detected in three orthogonal planes. Volumes may be calculated using the formula: volume = length × width × height × 0.52. The TA technique provides the best overview of the pelvis, and is best for examining large masses, but is less comfortable for the patient because of the distended bladder.

For transvaginal (TV) examination, the patient is asked to empty her bladder and lie supine with her legs flexed. Folded sheets or pads are placed under her buttocks to elevate her pelvis above the examination table to allow room for transducer manipulation. Alternatively, the patient may be examined on a pelvic examination table with her feet in stirrups.
A 4.0-7.0-MHz TV US probe is coated with gel and is covered with a sterile condom that is also coated with gel. The probe may be placed in the vagina by the patient, the sonographer, or the sonologist. Prudence dictates that a woman should be in the room at all times during a vaginal sonogram, either as the examiner or as a chaperone [1]. The uterus is examined for size, shape, contour, orientation, and appearance of the myometrium, endometrium, and cervix. The ovaries are documented for size, shape, contour, echogenicity, and position. Any masses or abnormalities are evaluated for origin, echotexture, size, shape, and relationship to other organs. The cul-de-sac is examined for fluid and masses. Loops of bowel in the pelvis are inspected for peristalsis and wall thickening.

The TV technique offers better tissue characterization because of the ability to use high-frequency transducers. However, the field of view is limited and large masses may be overlooked. If TV examination is performed first, the pelvis should always be examined transabdominally, even if the bladder is empty, to check for abnormalities outside the TV field of view.

The translabial approach is particularly useful for examination of the vagina and cervix, and is an effective alternative for any patient unwilling or unable to undergo TV examination [2]. A 3.5-5.0-MHz sector transducer, covered with a transducer sheath and generously coated with gel, is placed on the labia. Examination is performed in sagittal and coronal planes along the long axis of the vagina.

A transrectal approach to pelvic US may also be used especially in patients unwilling or unable to undergo TV US. The transrectal approach offers similar advantages of placing the transducer closer to the organs of interest allowing higher frequency transducers with better resolution.

Sonohysterography (SHG) is a useful technique to examine the endometrium and uterine cavity [3, 4, 5]. The examination is easiest to perform with the patient on a pelvic examination table with her feet in stirrups. A speculum is used to visualize and cleanse the cervix with antiseptic solution. A 5-F pediatric feeding tube or a balloon SHG catheter, pre-filled with sterile saline solution, is placed into the cervix. If a balloon catheter is used, the balloon is distended in the cervical canal with 3-5 mL of water, not air. The speculum is removed and a TV US transducer is placed into the vagina. Using direct US visualization, saline is injected to distend the uterine cavity, detect polypoid masses, and to assess the appearance and thickness of the endometrium.

The size and shape of the uterus vary with age and parity. The uterus of the neonate, stimulated by maternal hormones as a fetus, is up to 1 cm longer and 1 cm larger in diameter than the uterus of a young child. The cervix is commonly twice as long and twice as thick as the body. By the end of the first year of life the uterus has become smaller and is sausage shaped. With puberty, the uterus assumes a pear shape with the body twice as large as the cervix. The uterus enlarges with multiparity and atrophies following menopause. Normal uterine dimensions are listed in Table 5.1.

The surface of the uterus is smooth and well defined (Fig. 5.1). A slightly indented isthmus separates the body from the cervix. The cervix is fixed in the midline of the pelvis,
but the body is often “flexed” and angled (“verted”) with respect to the cervix. The uterus is most commonly anteflexed and anteverted, lying on the bladder dome. A retroflexed uterus is bent at the isthmus with the body folded backwards on the cervix (Fig. 5.2). A retroverted uterus is straight but directed posteriorly. The body may also be angled toward the right or left pelvic sidewalls.

The myometrium is medium in echogenicity and granular in echotexture. Three layers of myometrium can often be recognized. The inner junctional myometrium is thin, compressed, hypovascular, and mildly hypoechoic compared to the thick homogeneous middle layer. The arcuate vessels, which are often prominent, divide the middle layer from the slightly hypoechoic outer layer (Fig. 5.3). Calcification of the arcuate arteries occurs in older women and diabetics (Fig. 5.4).

The endometrium varies in thickness and appearance with the degree of stimulation by hormones, primarily estrogens and progesterones (Table 5.2). In the neonate, because of maternal hormones, the endometrium is brightly echogenic but thin. In the prepubertal child, the endometrium remains thin and is nearly isoechoic with the myometrium. Following puberty, the endometrial appearance varies with the menstrual cycle [6]. In the proliferative phase (Fig. 5.5A), prior to ovulation, the endometrium assumes a three-layer appearance as it thickens to 4-8 mm. The central line, which defines the endometrial cavity, is echogenic. The proliferating functional layer, which will slough with menstruation, is hypoechoic. The outer basal layer, which remains intact throughout the menstrual cycle, is echogenic and surrounded by the hypoechoic junctional zone of the myometrium. In the secretory phase, following ovulation, the functional layer continues to thicken and becomes echogenic (Fig. 5.5B). The entire double-layer thickness of the endometrium in the secretory phase is 7-14 mm. During menstruation, the functional layer is lost and the
remaining basal endometrium appears as a thin, broken, irregular echogenic line. Following menopause, the endometrium atrophies, thins (to <4 mm), and becomes less echogenic. Hormone replacement therapy in the postmenopausal woman will stimulate the endometrium. Unopposed estrogen has the greatest effect. Sequential hormone replacement, with estrogen followed by progesterone, causes the endometrium to change to an appearance very similar to the premenopausal woman.

The fallopian tubes extend laterally from the uterus in the free edge of the broad ligament. Each is 7-12 cm in length and consists of an intramural portion traversing the myometrium, a cord-like isthmus, a wider and tortuous ampullary portion, and the funnel-shaped, fimbriated infundibulum that opens into the peritoneal cavity. The fallopian tubes are not appreciated on US unless they are dilated or when peritoneal fluid defines the edge of the broad ligament.

The ovaries are elliptical in shape and lobulated in contour. Follicles project from the outer cortex, and the stroma and blood vessels occupy the inner medulla (Fig. 5.6). The ovaries are attached to the uterus by a fold of the broad ligament called the ovarian ligament, and to the pelvic sidewall by the suspensory ligament of the ovary. The fallopian tubes in the broad ligament and the mesosalpinx drape over the ovary. The ovaries are
imaged in a shallow fossa anterior to the internal iliac vessels and medial to the external iliac vessels. The ovaries are displaced cephalad by increasing bladder distention. When the uterus is positioned toward the pelvic sidewall, the ipsilateral ovary is frequently located cephalad to the fundus. When the uterus is retroverted, the ovaries are usually ventral to the uterus at the level of the uterine body.

The size and appearance of the ovaries change with age and with phase of the menstrual cycle (Table 5.3) [6]. In children younger than 8 years of age, the ovaries are homogeneous and solid [7]. Occasionally small follicles (<9 mm) are present. Normal follicles appear as anechoic, thin-walled cysts on the periphery of the ovary. In the follicular (proliferative) phase of the menstrual cycles, elevated levels of follicle-stimulating hormone and luteinizing hormone stimulate the development and enlargement of a variable number of follicles [6]. One follicle becomes dominant and matures as the Graafian follicle. This dominant follicle reaches a size of 20-25 mm, whereas most of the other follicles involute. Ovulation occurs when the dominant follicle ruptures, releasing the ovum and 15-25 ml of fluid into the peritoneal cavity. Mid-cycle pain, “mittelschmertz,” coincides with ovulation. The corpus luteum develops at the site of the ruptured dominant follicle. Blood clot and fibroblasts invade the collapsed follicle, which becomes intensely vascular and reforms a lymph and blood-filled cyst. The corpus luteum produces progesterone that supports the secretory endometrium to allow successful implantation if fertilization of the ovum occurs. The corpus luteum will degenerate in 14 days in the absence of an intervening pregnancy.

Size of the ovary is evaluated by measurement and calculation of volume using the standard formula (length × width × height × 0.52). Normal values are given in Table 5.3 [8, 9, 10]. The ovaries shrink with age after menopause [10].

The ovaries have a dual blood supply from the ovarian artery and from an adnexal branch of the uterine artery. Spectral Doppler shows high resistance flow in the first half of the menstrual cycle and low resistance flow in the second half after formation of the corpus luteum. The ovaries are hypovascular after menopause with flow detected only in the main ovarian artery.

The cul-de-sac frequently contains a small volume of fluid (~10 cc) that is best seen on TV US. A small volume of fluid is normal and physiologic (Fig. 5.7). The volume of fluid is increased with ovulation.

The normal vagina is a muscular tube in the midline of the pelvis extending from the vestibule of the external genitalia to the cervix. The cervix projects into the vaginal apex and is surrounded by vaginal recesses called the fornices. On sagittal images, the vagina appears as a tubular structure with hypoechoic muscular walls and a bright linear central echo caused by the apposing surfaces of the vaginal mucosa (Fig. 5.1). On transverse images (Fig. 5.8), the vagina appears as a flattened oval or flattened H-shaped structure with folds of vaginal mucosa laterally and the urethra coursing prominently in the anterior vaginal wall.