The ability of sonography, in particular transvaginal sonography (TVS), to depict subtle changes in the myometrium and endometrium makes it the diagnostic modality of choice for the evaluation of many uterine disorders. With sonography, the uterus can be imaged in several scan planes. Because the images are obtained in real time, and uterine orientation can be variable, the sonographer can empirically alter the scanning plane and gain settings for optimal depiction of the endometrium and myometrium. Because of its proximity to the uterus, a transvaginal transducer/probe can enhance the sonographic depiction of the uterus and endometrium.

Once a uterine lesion is suspected clinically, TVS can be used to establish the presence, size, extent, and internal consistency of the lesion and to detect associated pathology, such as liver metastases. Sonography has a major role in differentiating palpable uterine masses from those that arise from adnexal structures. The specific diagnosis can be confirmed by endometrial biopsy or through dilation and curettage (D&C). Alternatively, other imaging techniques, such as hysterosalpingography and, in some cases, even direct hysteroscopic visualization may be useful. Magnetic resonance imaging (MRI) and computed tomography (CT) can also demonstrate uterine and parauterine anatomy, and are particularly useful in staging known uterine neoplasms.

TVS has an important role in establishing the presence of diffuse and/or localized adenomyosis, a common cause of abnormal uterine bleeding characterized by endometrial glandular extension into the myometrium. On TVS, adenomyosis appears as an irregular myometrial texture including a “venetian blind” pattern secondary to fibrosis that occurs surrounding a myometrial implant.¹ Another TVS finding in adenomyosis is apparent disruption in the outer endometrial—inner myometrial interface as seen on a coronal three-dimensional ultrasound (3DUS). Although the TVS findings may be subtle at times, the solicitation of pain when the transducer is pressed up against the uterus is another useful hint to the probability of adenomyosis.

Transrectal sonography (TRS) and transabdominal sonography (TAS) may be useful in certain operative uterine procedures such as negotiating a stenotic cervical canal, completing difficult D&Cs, and placing a tandem within the uterine lumen for localized radiation therapy of cervical carcinoma.

3D sonography has been shown to be useful in the evaluation of uterine anomalies. 3DUS affords depiction of the uterine fundus in the coronal plane, which is vital in distinguishing a bicornuate uterus from a septate uterus. Please refer to Chapter 49 for a more extensive discussion.

This chapter discusses and illustrates the sonographic features of the most common uterine malformations and disorders. Sonographic evaluation of the endometrium is discussed in detail in Chapter 35. For the sonographer and sonologist to distinguish normal from pathologic findings, a short discussion of the sonographic features of the normal uterus follows comments concerning scanning technique.

Both TVS and TAS have an important role in the imaging evaluation of the uterus. Whereas TVS affords detailed images of the uterus, patients with larger uteri or masses larger than 5 cm may be better depicted by TAS. 3DUS is frequently a helpful diagnostic modality in several uterine/endometrial disorders including uterine malformations, definitive diagnosis of adenomyosis, and in the assessment of size, extent, and location of fibroids.

For TAS, sonographic evaluation of the uterus should be performed when the patient has a fully distended bladder, which displaces gas-filled bowel loops from the pelvis and places the uterus in a more horizontal plane. This orientation of the uterus relative to the transducer is advantageous because the uterus can be imaged by using the superior characteristics of axial as opposed to lateral resolution. However, the urinary bladder can be overly distended on occasion, placing the uterus out of the focal range of a focused transducer. In such cases, partial voiding will place the uterus in a more optimal focal range. In some patients with very large uterine masses, full distention of the bladder may be impossible, and adequate sonographic visualization of the uterus must be attempted without this benefit.

When examining a pelvic mass thought to be of uterine origin, it is important to establish the continuity of that mass with the uterus.² This entails establishing that the vagina leads into the mass and that a linear echogenic interface in the uterus—the endometrium—is present. TVS with 3DUS can be used to optimize depiction of these features. (Please see Chapter 49 for a detailed discussion of 3DUS of uterine and endometrial disorders.)

For TVS, the urinary bladder should not be overly distended. The uterus should be imaged in its long axis first, sweeping from right to left by angulating the probe. Short-axis images are then obtained. The relative position of the uterus can be inferred by the orientation of the probe that best images the uterus. For example, if the uterus is best imaged with a posterior inclination, the uterus is probably retroflexed.

When evaluating the uterus with TVS, the examiner should also evaluate the relative thickness and texture of the bladder wall. Occasionally, excresences that arise from the bladder wall, which represent polypoid lesions, may be detected.

The endometrium can be demonstrated in most patients as an echogenic interface or a group of interfaces in the center of the uterus (also known as endometrial “interfaces” or endometrial “stripe”). The sloughed pieces of the endometrium during menstruation usually produce a thin, broken echogenic interface. The endometrium thickens and becomes echogenic as it develops in the secretory phase. The thickness of the endometrium can usually be estimated by the distance from the proximal to distal interfaces between the hypoechoic halo that surrounds the endometrium (corresponding to the compact and relatively hypovascular inner layer of myometrium) and the more echogenic endometrium. The “natural contrast” provided by the endometrium can be used to definitively localize the uterus in relation to other masses that may surround or distort it.³

3DUS is useful in evaluation of the uterus for distinguishing bicornuate from septated uteri particularly as depicted in the coronal plane. 3DUS can be obtained using a freehand technique or a transducer capable of an automated sweep or one with multiple subelements in a matrix array. (Please refer to Chapter 49 for more details.)

Sonography can accurately depict the position, size, shape, and texture of the uterus. Indeed, each of these features should be carefully assessed and documented sonographically (Figures 34-1, 34-2, 34-3, 34-4).

The position of the normal uterus is immediately posterior to the floor and dome of the urinary bladder. The fundus is usually oriented anteriorly when compared with the cervix with the plane of the endometrial cavity extending anteriorly (up to perpendicular) with respect to the plane of the vagina (anteverted), although a retroverted uterus can be seen as a normal variant. When observed in the midline axial plane, the linear relationship between the endocervical canal and the endometrium should be evaluated; most are somewhat aligned. However, if the endometrial axis is deflected anteriorly with respect to the endocervical axis, the uterus is said to be anteflexed. A posterior deflection is retroflexed. Retroverted uteri appear more lobular in contour than anteverted uteri, in part because there tends to be altered venous drainage with consequent myometrial suffusion. Transvaginal scanning can improve depiction in most of these cases. Because of the posterior position and curved surface of the fundus, however, it may be difficult to obtain detailed images of the fundal portion of a retroverted uterus. Furthermore, the endometrial layer may not be seen with TAS. In some severely retroverted uteri, an interface perpendicular to the endometrial lumen can be seen; this probably results from an indentation and compression of the myometrium and uterine serosa.

On transverse sonograms, a significant range of variation in the right-to-left or anterior–posterior position of the uterus can be observed in normal individuals. These positional variants are in part dependent on the degree of bladder and rectal distention present when the patient is examined.

The flexion and position of the uterus are not as readily depicted by TVS as by TAS. In general, if the uterus is best depicted on TVS when there is a posterior orientation of the probe, the uterus is most likely retroverted. Conversely, if the uterus is best depicted when the probe is placed in the posterior vaginal fornix and aimed anteriorly, the uterus is most likely anteverted.

Before discussing the size and shape of the uterus, the various anatomic segments of the uterus are noted here. There are three main divisions of the uterus: the fundus, the corpus or body, and the cervix. The segment of the uterus that lies superior to the entrance of the uterine tubes is designated the fundus. Inferior to the fundus and superior to the internal cervix is the corpus. The lower portion of the corpus and its approximation with the cervix is sometimes termed the “lower uterine segment” or isthmus. Although the isthmus has been designated as a separate segment of the uterus, this designation is debatable because it is not distinct—on the basis of anatomy—from the corpus. There is a transition from the smooth muscle wall of the fundus and corpus to the cervix, which consists of mostly fibrous tissue.

The size and shape of the uterus differ according to the patient’s pubertal status, age, and parity.^4-6 Before puberty occurs, the uterus measures 1.0 to 3.3 cm in length and 0.5 to 1.0 cm in width. The cervix and isthmus comprise a greater proportion of the uterus (up to two-thirds of the total length) and are thicker than the fundus. In contrast, the nulligravidous, normal postpubertal uterus measures 7 cm in length, 4 cm in width, 4 cm in height and has a relatively thicker fundus and shortened cervix. The multiparous woman typically has a uterus that measures an average of 1.2 cm greater in all directions, compared with the nulligravida.⁵ A postmenopausal woman has a uterus that is smaller than the normal postpubertal woman. The average dimension of the postmenopausal uterus ranges from 3.5 to 6.5 cm in length and is 1.2 to 1.8 cm thick.⁶

The texture of the normal myometrium is consistent throughout all age groups and is of a homogeneous low to medium echogenicity. Small “arcuate” vessels (between 1 and 2 mm in diameter) can sometimes be seen between the middle (spiral) and outer layers of myometrium.⁷ It is also not unusual to have calcification of these arcuate arteries in the outer layers of myometrium in older women. The inner layer of myometrium is thin and hypoechoic, which corresponds with the “junctional zone” seen on MRI. The spiral, or middle, layer of myometrium is the thickest layer, and its muscle bundles are arranged concentrically. Variations in the arrangement of myometrial muscle bundle may produce focal areas of irregular echogenicity. This may also be seen in focal areas of myometrial contraction. These should be distinguished from fibroids.

Sonography, in particular TVS, can depict a variety of appearances of the endometrium that correspond to the major developmental stages (menstrual, proliferative, or secretory). The innermost layers of the endometrium appear as a central linear echogenicity that is most prominent during menses. Surrounding this echogenic interface is a hypoechoic band that probably corresponds to the compact and relatively hypovascular inner layer of the myometrium. The endometrium thickens from 5 to 7 mm (in the proliferative phase) to 7 to 12 mm (in the secretory phase) in total anterior–posterior width.⁷ The hypoechoic texture of the endometrium most frequently seen in the proliferative phase is related to the particular arrangement of the enlarging glands and stroma. Stromal edema occurring in the secretory phase most likely also contributes to the echogenic texture of the endometrium during this portion of the cycle by increasing the number of interfaces between glandular and stromal elements. A small amount of intraluminal fluid can be observed during the periovulatory and secretory phase of the cycle.⁷ In addition, the innermost layer of endometrium may be edematous, giving rise to a multilayered pattern (as seen in long axis) or a “halo” configuration (as depicted on transverse scans).⁷ The endometrium appears thickened and echogenic during the secretory phase. The echogenic texture of the secretory endometrium is probably related to the hypertrophied and tortuous glands, which contain a mucinous secretion. The mucus contained within the endocervical canal is observed to become more hypoechoic near the time of ovulation, which is probably related to the high fluid content.

The endometrium in postmenopausal women, especially those not taking hormone replacement therapy, should be relatively thin (most frequently <6 mm) because it is typically atrophic. There may be focal areas of calcification in the outer myometrium, representing calcified arcuate arteries and/or veins. These may be particularly extensive in diabetic patients. Echogenic foci within the myometrium may also represent focal areas of fibrosis secondary to prior curettage or other uterine instrumentation, or to microcalcifications due to retained foci of decidua from prior pregnancies. A small amount of intraluminal fluid can be seen in normal patients.⁸

On pelvic examination, a malformed uterus may be confused with an adnexal mass (Figure 34-5). Similarly, the sonographic appearance of malformations is sometimes mistaken for uterine fibroids.⁹ The most common congenital uterine malformations arise from anomalies of fusion. A T-shaped uterus is associated with a history of diethylstilbestrol (DES) ingestion by the mother of the patient. Hematometra and/or hydro- or hematocolpos can be secondary to congenital malformation, especially if they occur together (hematometrocolpos), but it also can be acquired secondary to cervical stenosis.^12,13 Each of these entities is discussed as it relates to sonographic findings. Some patients with a uterine anomaly may have (usually unilateral) anatomic abnormalities of the urinary tract such as a duplicated, abnormally routed, or absent collecting system, renal anomalies, or even renal agenesis.¹¹

3D sonography has become the diagnostic modality of choice for the evaluation of uterine malformations. This is true because of its ability to depict the contour of the fundus in the coronal plane. Using this, one can readily distinguish a bicornuate uterus from a septated uterus because a bicornuate uterus has a fundal indentation whereas a septated uterus does not.

Fusion Anomalies—Bicornuate Versus Septated Uterus

Early in embryonic development of the female fetus, the Wolffian and Müllerian duct systems interact to form the internal genitalia. The Wolffian system regresses, and the uterus, oviduct, ovary, and vagina are formed from paired Müllerian structures that eventually fuse in the midline.

The most common anomalies of the internal genitalia result from defects in fusion of the paired Müllerian structures that form the uterus, cervix, and vagina. The degree of failure can range from partial to complete. If there is total failure of fusion, a uterus didelphys will result. In patients with uterus didelphys, two cervices and two uteri are present; a longitudinal septum (at least in the upper 2/3 of the vagina) is frequently present, with each vaginal canal leading to a unique cervix and uterine horn. Partial fusion of the Müllerian duct derivatives range from uterus bicornis unicollis (the suffix cornis refers to the uterine horns and collis refers to the cervix, thus two uterine horns, one cervix) to uterus arcuatus (mildest fusion anomaly, with saddle-shaped lumen and apparent “funneling” of the cornuae). In all of these fusion anomalies, a common central wall between the two uteri is present. Incomplete resorption of the sagittal septum within the uterus results in a uterus septus or subseptus, depending on the size of the septum.

Arrested development of the Müllerian ducts results in uterine aplasia; if this occurs unilaterally, a uterus unicornis unicollis is formed.

Other anatomic defects may be associated with uterine malformations. Specifically, renal anomalies, and in particular renal agenesis, may be encountered on the same side as the uterine malformation.⁹ Thus, if a uterine anomaly is suspected, one should scan the region of the kidneys.

Duplication of the uterus can be associated with a noncommunicating or otherwise obstructed horn, resulting in hematometra. A bicornuate uterus can mimic the sonographic appearance of a parauterine solid mass; however, the typical pear shape of the uterus can be recognized on real-time exam of the latter. Sonographic recognition of a uterine septum in a gravid patient is important because of increased risk of spontaneous abortion or predisposition to premature labor, fetal malpresentation, and third trimester bleeding.

One of the most common uterine anomalies detected on sonography is the gravid bicornuate uterus (Figure 34-6). Commonly, the patient with this condition presents with unexplained uterine bleeding during the first trimester secondary to sloughing of the decidua in the nongravid horn. Sometimes the anomaly is first discovered when a nodular mass is palpated. Indeed, the empty horn of the uterus can be mistaken for a parauterine mass on pelvic examination.

The nongravid bicornuate uterus usually appears sonographically as a binodular structure that is best delineated on transverse scans. It can appear quite similar to leiomyomata, except that the myometrium has a homogeneous texture as opposed to the whorled appearance of a leiomyoma. Additionally, during menstruation, two uterine lumina may be identifiable.

Hydrometrocolpos and Hematometrocolpos

These conditions can be associated with either congenital or acquired malformation of the uterus or vagina.^10-12 They result from accumulation of secretions or blood within the uterus or vagina, which occur because of congenital or acquired obstruction of a uterine horn, cervix, or vaginal tract.

Obstruction of menstrual flow can be congenital and symptomatic, as in delayed menarche with transverse vaginal septum, imperforate hymen, or vaginal atresia, or it can be asymptomatic, as in a blind horn. Previously healthy women may have obstruction of the uterine outflow tract from a neoplastic process or from postinfectious or postoperative scarring. In any of these cases, retrograde menstruation can occur.¹²

Premenarchal girls may accumulate clear secretions in the vagina, even relatively large amounts. Patients with this condition may be asymptomatic but can present with vague pelvic discomfort or pain during defecation or urination due to compression of the rectum or bladder by the pelvic mass. Similar to delayed menarche in the otherwise healthy girl, hematometrocolpos can be encountered in patients with a transverse vaginal septum, an imperforate hymen, or vaginal atresia.

Sonographically, the distended uterus or vagina appears as a pear-shaped structure with either anechoic or echogenic internal contents. If clotted blood is contained within the uterus, echoes emanating from the clotted blood can be seen. These are usually mobile when the patient is scanned in various positions.

A small amount of fluid or blood can be present within the endometrial cavity during menstruation or in pelvic inflammatory disease. Intraluminal fluid may be associated with endometritis with or without pelvic inflammatory disease involving the fallopian tubes and ovaries. In postmenopausal women, intraluminal fluid can be associated with endometrial or fallopian tube carcinoma.¹⁴

If there is an imperforate hymen, transperineal scanning can be used to assess the vagina and uterus.

T-Shaped Uterus

A specific uterine anomaly has been encountered in women whose mothers received DES as part of a therapeutic regimen. DES was widely prescribed to pregnant women between 1940 and 1960 as an antiabortifacient. A great many women who were exposed to DES in utero have multiple benign abnormalities of the genital tract.¹⁰ In addition, more than 300 cases of clear-cell adenocarcinoma of the vagina have been reported to date.

Sonography can be useful in detecting the so-called T-shaped uterus associated with DES exposure. The volume of the T-shaped uterus, calculated from length, width, and anterior–posterior dimension, has been reported to be significantly less than a control group of women at similar ages.¹⁰ The T-shaped uterus derived its name from the hysterographic appearance of the uterine lumen. The abnormal shape and decreased size of the uterus can be detected sonographically by a greater-than-usual transverse dimension and by decreased thickness of the fundus.¹⁰ 3DUS can definitively diagnose most uterine anomalies such as a septate versus bicornuate uterui.^15-17 Uterine anomalies are classified according to American Fertility Classification (see Figure 34-5).¹⁸

Sonohysterography may be helpful in defining the endometrial lumen in malformed uteri. Similarly, sonographic delineation of the endometrium, particularly in the luteal phase, can also be helpful in the assessment of a malformed uterus. Particular attention should be directed toward assessment of the uterine fundus because bicornuate uteri have a definite cleft as opposed to septated uteri, which do not.