The sonographic appearance of the normal endometrium depends on the menstrual phase or status of the patient and should be homogeneous in appearance and of appropriate thickness for the woman’s menstrual status (Table 13-1). An AP measurement of the double layer endometrial thickness should be obtained while in the longitudinal scanning plane, with placement of the calipers at the outer edges of each echogenic basal layer (Fig. 13-4, A). When intercavitary fluid is present, the endometrial layers should be measured separately, with the sum of the two measurements representing endometrial thickness (Fig. 13-4, B). For menstrual age women, normal double layer endometrial thickness is 4 to 14 mm, with maximum thickness occurring during the secretory phase. Endometrial pathology is very unlikely in a postmenopausal woman if endometrial thickness is less than 5 mm.² Postmenopausal women taking hormone replacement therapy can experience a slightly thickened endometrium during the estrogen cycle (up to 8 mm) and should undergo repeat scanning during the progesterone cycle.

TABLE 13-1

Normal Endometrial Thickness (mm)

Early Proliferative Phase	Periovulatory (Late Proliferative) Phase	Secretory Phase	Postmenopausal (No HRT)
4-8	6-10	7-14	1-4

HRT, Hormone replacement therapy.

From Salem S: Gynecologic ultrasound. In: Rumack C, Wilson S, Charboneau J, et al, editors: Diagnostic ultrasound, vol 1, ed 4, Philadelphia, 2011, Mosby:547-612.

The functional layer of the endometrium demonstrates changes in sonographic appearance throughout the menstrual cycle. During menses, the endometrium is thin and appears as a hyperechoic line (Fig. 13-5, A). As the proliferative phase progresses and ovulation approaches, a triple line appearance is created by the opposite hyperechoic basal layers, hypoechoic functional layer, and hyperechoic endometrial cavity (Fig. 13-5, B). The secretory phase results in a thickened endometrium hyperechoic to the myometrium (Fig. 13-5, C). The inner layer of myometrium adjacent to the basal layer of the endometrium appears as a hypoechoic rim and is sometimes referred to as the junctional zone or subendometrial halo (Fig. 13-6); this should not be included in endometrial measurements.

FIGURE 13-5 **(A),** Early proliferative phase demonstrates thin endometrium. **(B),** Late proliferative phase demonstrates triple line appearance of endometrium. **(C),** Secretory phase demonstrates thicker, hyperechoic appearance.

The normal myometrium has a homogeneous echotexture, and the sonographer should assess for focal masses, diffuse heterogeneity, distortions in uterine contour, and size. The uterine veins are larger than the arteries and can be identified sonographically as focal anechoic areas around the periphery of the uterus (Fig. 13-7). In older women, atherosclerotic changes within the arcuate arteries of the uterus may be seen as hyperechoic, shadowing foci around the periphery of the uterus (Fig. 13-8).

FIGURE 13-7 Anechoic spaces *(arrows)* around the periphery of the uterus are normal uterine veins and should not be mistaken for an abnormality.

Although there are many causes of AUB in a nonpregnant patient, sonographic assessment for endometrial and myometrial abnormalities is important because they are a common cause of AUB. Endometrial abnormalities may appear sonographically as a thickened endometrium, a focal mass, or a heterogeneous endometrium. Some common endometrial abnormalities that are discussed in this chapter include endometrial hyperplasia, endometrial carcinoma, polyps, changes caused by tamoxifen therapy, and retained products of conception. The most common cause of postmenopausal bleeding is endometrial atrophy, which appears sonographically as an endometrium less than 4 mm in thickness. Common myometrial abnormalities resulting in AUB include leiomyomas and adenomyosis. Myometrial abnormalities may affect the sonographic appearance of the uterus in the following ways: diffuse heterogeneity, focal hypoechoic or hyperechoic masses, distortion of the uterine contour, or overall uterine enlargement.

Myometrial Abnormalities

Leiomyoma

Leiomyomas, also called myomas or fibroids, are benign smooth muscle tumors that develop within the myometrium, but they may intrude into any of the uterine layers (Fig. 13-9). Uterine fibroids represent the most common pelvic tumor and are a leading cause of hysterectomy. Less commonly, fibroids can develop within the vagina, cervix, broad ligament, or fallopian tubes or on the omentum (so-called parasitic fibroids). They are more common in African American women than in women of other ethnicities.³ Fibroids range in size from 1 mm to more than 20 cm. Many women have multiple fibroids of varying sizes. Fibroids are known to grow in response to estrogen stimulation and tend to stabilize or regress during menopause.

FIGURE 13-9 Illustration of cut uterus showing classification and location of fibroids.

Fibroids are myometrial in origin, and they can be surrounded by myometrium, intrude into the endometrium, or come in contact with the serosal layer (Fig. 13-10). Fibroids surrounded predominantly by myometrium are the most common and are referred to as intramural fibroids. Fibroids that project into the endometrium are referred to as submucosal fibroids. Subserosal fibroids are in contact with the serosal layer and distort the uterine contour. In some cases, subserosal fibroids grow off of a stalk into the adnexal regions seemingly separate from the uterus; these are referred to as pedunculated fibroids. Generally, only submucosal or large intramural fibroids cause AUB. Pedunculated fibroids are remote from the endometrium and myometrium and typically do not cause menorrhagia. The exact cause of menorrhagia with fibroids is unknown, but fibroid-associated changes in uterine vasculature, contractility, and endometrial surface area may contribute to the problem.⁴ Fibroids can undergo degeneration, which may cause pain.