27 ULTRASOUND EVALUATION OF THE UTERUS
IMAGING
The American Institute of Ultrasound in Medicine (AIUM) guidelines for imaging of the uterus have been developed to assist sonologists in performing sonographic studies of the female pelvis.1 Knowing the potential but also the limitations of ultrasound helps us to maximize the probability of detecting most significant abnormalities. As with any clinical test, ultrasound of the pelvis should be performed only if there is a valid clinical reason. Following the AIUM guidelines, the indications for pelvic sonography include, but are not limited to
Techniques
For transvaginal evaluation, the urinary bladder should be emptied and the patient in comfortable position but with her pelvis tilted either with the use of stirrups or with an elevation under the hips. The patient or the sonographer, depending on the patient’s preference, may introduce the vaginal transducer with real-time monitoring. For transvaginal evaluation, the AIUM recommends using probes of 5 MHz or higher (Fig. 27-2) If a male sonologist is performing the examination, a female member of the staff should be present as a chaperone.

FIGURE 27-2 A. Sagittal-transvaginal view of the normal uterus. B. Transverse-transvaginal view of the normal uterus.
The vagina, uterus, and the urinary bladder are used as reference points for identification of the remaining normal and abnormal pelvic structures. The uterine size, shape, and orientation should be identified and documented in sagittal and transverse axial planes. The endometrium, myometrium, and cervix should be carefully evaluated, and their appearance documented. The uterine length is measured in long axis from the fundus to the cervix, and the anteroposterior dimension is measured on the same image perpendicular to the length. The width is to be measured on a separate image on either a transaxial or coronal plane of section. If the volume of the uterine corpus is assessed the cervical component should be excluded.1
Assessment of the endometrium is performed in a sagittal plane. Variations of the appearance of the endometrium with different phases of the menstrual cycle and with hormonal supplementation should be considered (Fig. 27-3). Myometrial masses and contour abnormalities should be recorded in two different planes and their locations recorded.1 Doppler evaluation of the uterus and endometrium can be of added value.
SIS is contraindicated in women who could be pregnant or have an active infection. Because the normal secretory endometrium may be thick and simulate endometrial disease, the examination should be scheduled in the follicular phase of the cycle, after menstrual flow has ceased but prior to ovulation, no later than the 10th day of the menstrual cycle. Active vaginal bleeding is not generally a contraindication but can make imaging challenging or even nondiagnostic.2
At our institution, we perform a preliminary transabdominal and transvaginal sonogram before SIS. After the procedure is explained to the patient, the external os is cleansed before catheterization of the cervical canal using aseptic technique. A sonohysterography catheter (flushed with saline to remove any air bubbles) is then advanced into the endometrial canal. Once in the endometrial canal, the balloon is inflated so that the catheter does not become dislodged. The speculum is removed, and the transvaginal probe is reinserted adjacent to the catheter. Under ultrasound guidance, the balloon is gently retracted to occlude the internal os. Sterile saline should be administered under real-time sonography. The amount of saline one introduces is variable, often between 5 and 30 mL. Normal anatomy and abnormal findings should be documented in two separate planes using the high-frequency transvaginal (TV) probe extending from one cornua to the other (Fig. 27-4)
ANATOMY
The uterus is physiologically most often anteroverted and anteroflexed (Fig. 27-5) but may also be retroflexed (Fig. 27-6) or retroverted (Fig. 27-7). The cervix of the uterus is fixed in the midline but the body of the uterus can be mobile, and may change with varying degrees of bladder and rectal distention. Descriptions of flexion refer to the relationship of the body of the uterus to the cervix (usually the angle is about 270 degrees), whereas version refers to the cervical relationship to the vagina.
Retroversion and retroflexion are not infrequent in the nongravid state. In these cases the fundus of the uterus is positioned in the sacral hollow. During pregnancy, by the 14th to 16th week of gestation, the uterus enlarges and physiologically undergoes reduction. The fundus and uterus then rise into the false pelvis. If this fails to happen, the uterus becomes “trapped” in the sacral hollow, often referred to as “incarcerated.” As the gestation evolves, the cervix is drawn upward either against or above the symphysis pubis, resulting in distortion of bladder and urethra. The posteriorly positioned fundus can cause pressure on the rectum. Usually, patients present between 13th to 17th week of pregnancy with symptoms of bladder outlet obstruction. A history of multiple trips to the emergency room for bladder outlet obstruction should raise suspicion. A constellation of three findings on sonography is diagnostic of an incarcerated uterus. First, the pregnancy is deep within the cul-de-sac. Second, the maternal urinary bladder lies anteriorly rather than inferiorly to the uterus and marked bladder distention is noted. Third, a soft tissue structure (the cervix) is seen between the bladder and pregnancy. This appearance can be misconstrued as an empty uterus associated with an ectopic or abdominal pregnancy. Failure to recognize an incarcerated uterus can result in compromise of the uterine circulation, leading to spontaneous abortion or even uterine rupture. If recognized early, manual uterine repositioning usually is accomplished (Fig. 27-8)
The shape and size of the uterus varies throughout life, affected mostly by hormonal status. The mean measurement of a prepubertal uterus is 2.8 cm in length and 0.8 cm in maximum anteroposterior dimensions, with the cervix accounting for two thirds of the total length and contributing to the pear-shaped appearance (Fig. 27-9).3 It is important to remember that in the immediate postdelivery state, the neonatal uterus can be slightly larger owing to the effects of residual maternal hormones. For the same reason, the echogenic endometrium is well seen and a small amount of fluid can be present in the endometrial cavity.
From birth until 4 years of age, the uterus decreases in size. At approximately 8 years of age the uterus starts to grow preferentially in the fundus. The uterus continues to grow for several years after menarche until it reaches the mean dimensions of a reproductive age uterus, which are approximately 7 cm long and 4 cm wide.
Parity increases the size of the uterus, with a multiparous uterus measuring approximately 8.5 cm by 5.5 cm.4
The postmenopausal uterus is often small. The decrease in size is related to years passed after menopause,4 although the reduction in size is believed to be most rapid during the first decade after menopause. The range can be from 3.5 to 6.5 cm in length and 1.2 to 1.8 cm in anteroposterior dimensions.5

FIGURE 27-11 Sagittal-transvaginal view of the uterus demonstrates arcuate artery calcifications (arrows).
Congenital Malformations
The incidence of congenital müllerian duct anomalies is estimated to be approximately 0.5%. They are often diagnosed during workup for infertility, frequent miscarriages, or menstrual disorders. As one might remember from the embryology, the two paired müllerian ducts ultimately develop into fallopian tubes, uterus, cervix, and the upper two thirds of the vagina. The lower two thirds of the vagina and the ovaries have a separate origin. Uterine malformations arise from three different causes: arrested developement of müllerian ducts, failure of fusion of the müllerian ducts, or failure of resorption of the median septum.