After reading this article the learner will be able to:

• Differentiate between normal and abnormal uterine anatomy
• Discuss uterine pathology
• Discuss 3D ultrasound
• Discuss endovaginal multiplanar reconstruction of the uterus

Transabdominal scanning
Endovaginal imaging
Three-dimensional imaging (3D)
Coronal scan plane
Mullerian Ducts
Hematometra
Leiomyoma
Saline Infused Sonohysterography (SIS); Sonohysterogram
Synechiae
Mulitiplanar display
Rendering
Beta-View
Compound Resolution Imaging
Speckle Reduction Imaging
Volume Contrast Imaging

For decades, diagnostic ultrasound has been the imaging technology of choice for evaluation of uterine and adnexal pathology. Traditionally transabdominal scanning has been performed with a full bladder allowing for visualization of the uterus and adnexa in transverse and longitudinal planes to the body. The introduction of endovaginal imaging allowed for imaging in planes longitudinal and coronal to the body. With three-dimensional imaging (3D), longitudinal and transverse planes of the uterus and adnexa can now be demonstrated. In addition, a third plane, the coronal view, can now be displayed allowing for an even more detailed evaluation of the uterus and adnexa. The coronal view of the uterus enables visualization of the shape of the uterus and endometrium along with the relationship of the cornua to the cervix. (Figure 1) Congenital uterine abnormalities can be more easily diagnosed, along with better localization of myomas and polyps. Prior to surgery, confirmation of a uterine anomaly may still be performed using MRI or laparoscopy. Although 3D imaging adds more information, it does not eliminate the need to acquire good two-dimensional images, as these are necessary to render into quality three-dimensional images.

Figure 1 - Reconstructed coronal view of the uterus demonstrating the cornua (arrows) and cervix, with a normal uterine contour.

There are many indications to perform a gynecologic ultrasound, including but not limited to abnormal menses, pelvic pain, abnormal pelvic exam, reproductive issues, and intrauterine device location. Conventional ultrasound is limited in the number of scan planes able to be viewed as discussed above. With the introduction of 3-dimensional ultrasound, multiple planes can be displayed allowing for better interrogation of the uterus (Figure 2) and adnexa. With the addition of the coronal view, congenital uterine anomalies are easier to detect and diagnose, as is the location of fibroids and polyps.

Figure 2 - Planar views of a normal uterus using Volume Contrast Imaging

Congenital Uterine Anomalies
The estimated incidence of uterine anomalies among all women is approximately 1 in 200¹. Congenital Uterine anomalies occur when the Mullerian ducts fail to form, fail to fuse, or from failure of the fused ducts (the septum) to dissolve. The American Infertility Society has divided congenital uterine anomalies into 7 categories:²

1. Vaginal agenesis occurs from a problem in the development of a section of both Mullerian ducts. It presents as an absence or hypoplasia of the uterus, proximal vagina, and, in some cases, the fallopian tubes. Vaginal agenesis can be partial or complete. The most common form is complete agenesis (Mayer-Rokitansky-Kuster-Hauser syndrome), which is combined agenesis of the uterus, cervix, and upper portion of the vagina. Urinary tract and skeletal anomalies are often associated with this malformation.
2. Unicornuate uterus (Fig 3) occurs with the failure of one of the Mullerian ducts to form properly. Most women with a unicornuate uterus also have a second smaller or rudimentary uterine horn. The rudimentary horn can be solid or it can have a small cavity with a functioning endometrium. Sometimes the smaller horn connects to the uterus and vagina, but more often it is isolated or non-communicating. Associated urological anomalies are common such as ipsilateral renal agenesis especially when the rudimentary horn is obstructed. Obstetric outcomes are generally poor with up to 51% leading to spontaneous abortion.
3. Didelphys: If the Mullerian ducts fail to fuse at all, a complete duplication of the uterus, cervix and vagina can occur. Frequently vaginal duplication occurs and is characterized by a longitudinal septum extending either completely or partially from the cervices to the vaginal opening. Occasionally transverse septa can form and cause obstruction to one of the uterine horns, although uncommon. When completely obstructed, a hematometra (Figure 4) can occur and generally presents as a pelvic mass with or without pelvic pain. When diagnosed, it is frequently associated with ipsilateral renal and ureter agenesis. Reproductive outcomes are slightly better than with Unicornuate uteri with no compromise in fertility but an approximate 40% second trimester spontaneous abortion rate.
   

   Figure 3 - Unicornuate uterus

   Figure 4 -Didelphic uterus with Left sided hematometra (Image from Dr. Charles Miller's office)

   
   
4. Bicornuate: Development of a bicornuate uterus occurs when the Mullerian ducts incompletely fuse at the level of the uterine fundus. In this anomaly, the lower uterus and cervix are completely fused, resulting in 2 separate but communicating endometrial cavities with a single-chamber cervix and vagina. The bicornuate uterus has a midsagittal indentation of the external fundus of at least 1 centimeter in depth and a muscular uterine septum. Depending on the extent of this septum the bicornuate uterus is classified as either complete or partial. In the complete classification the septum extends to the internal os; this is known as a bicornuate unicollis uterus. Another variant of the complete form of bicornuate uterus is the bicornuate bicollis uterus, (Figure 5) in which the septum extends to the external os. When the septum is confined to the fundal region, it is considered a partial bicornuate uterus.
   
   

   Figure 5 - Bicornuate Bicollis Uterus

5. The septate uterus is the result of the failure of the degeneration of the median septum and is the most common Mullerian Duct anomaly. This type of anomaly usually has a normal external uterine contour, but may have a slight indentation of 1 centimeter or less. The uterine cavity is divided partially (Figure 6A) or completely (Figure 6B) by a septum of variable thickness. A sub-septate uterus occurs if resorption of the lower part of the median septum occurs, but the top of the septum fails to dissolve. The complete septate uterus may include a septate vagina and/or cervix. Fertility itself does not appear to be compromised with this type of anomaly, however a spontaneous abortion rate of up to 67% has been reported.³
   
   

   Figure 6A -Subseptate Uterus

   Figure 6B - Complete Septate

   
   
6. The arcuate uterus is normal in shape with a small midline indentation of the uterine cavity. The indentation results from the failure of the median septum to completely dissolve. (Figure 7) This uterine anomaly is essentially normal, but is still given a distinct class.
   
   

   Figure 7 - Arcuate uterus

7. Exposure to diethylstilbestrol (DES) during the embryonic period predisposes women to abnormalities of the uterine cavity. The external uterine contour is normal, with the uterine cavity hypoplastic and T-shaped, along with cervical defects. (Figure 8)
   

   Figure 8 - DES Uterus

Fibroids
Uterine fibroids also known as leiomyomas, are benign tumors made of smooth muscle cells and fibrous tissue that grow within the wall of the uterus. They may grow as a single tumor or in clusters, and are not associated with malignancy. Currently little is known about the cause of uterine fibroids. They are divided into three groups depending on their location. Submucosal fibroids grow just beneath the uterine lining, Intramural fibroids grow in between the muscle layers of the uterus, and Subserosal fibroids grow on the outside of the uterus. Others can grow on stalks that grow out from the surface of the uterus (pedunculated), or into the uterine cavity. Among all leiomyomas, the submucosal type is most likely to cause clinical problems.

Submucosal fibroids are further classified into 3 types: T0- completely within the cavity, T1- greater than 50% within the cavity, and T2-less than 50% within the cavity. If the fibroid projects into the lumen by more than 50% of its surface (T0 or T1), then it can be resected by hysteroscopy. This would replace a more involved abdominal surgical procedure. Fibroids generally have a heterogeneous echogenicity and often have posterior shadowing.

Adenomyosis
Adenomyosis is characterized histologically as benign invasion of the uterine musculature by the endometrium. The reported incidence of adenomyosis varies widely from one institution to another because adenomyosis is fundamentally a pathologic diagnosis. Adenomyosis is frequently accompanied by additional pelvic abnormalities such as uterine myomas, and it co-exists in 6–20% of patients with endometriosis. Adenomyosis is also associated with an increased incidence of endometrial hyperplasia and endometrial adenocarcinoma.⁵ It usually appears as diffuse disease, but may occur as a focal lesion (adenomyoma) similar in appearance to a myoma. (Figure 9) Ultrasonographically, adenomyosis may appear as an anechoic area of thickened myometrium, consisting of blood-filled, irregular cystic spaces, or as an area of hyperechoic myometrium with several cysts (hypoechoic lacunae).

Pelvic Inflammatory Disease
PID is an infection of the uterus, fallopian tubes, and/or ovaries. It occurs when disease-causing organisms migrate upward from the urethra and cervix into the upper genital tract. Untreated, PID causes scarring that may lead to infertility, tubal pregnancy, chronic pelvic pain, and other serious consequences. Infertility rates can increase after episodes of PID. The increased rate of infertility correlates most closely with the severity of tubal damage and the number of recurrent PID episodes.⁶ Aside from AIDS, pelvic inflammatory disease is the most common and serious complication of sexually transmitted diseases.

The ultrasound appearance of PID is varied and can be divided into five categories. 1. A normal pelvic ultrasound may be seen with acute inflammation involving only the fallopian tubes with no dilation. 2. With endometritis the endometrium is generally isoechoic to the myometrium and there may be fluid present within the cavity. No adnexal masses are present. 3. Hydrosalpinx: occasionally PID will appear unilateral. Generally the adnexal structure is anechoic, tubular, up to 4 cm in diameter with hyperechoic walls. 4. Pyosalpinx involves the adnexa unilaterally and approximately 1/3 of the time will also involve the cul-de-sac. The mass is usually well defined and clearly separable from the surrounding tissues. The walls are generally sharp and smooth, but can also be irregular and ill defined. The mass can range in size from 3-8 cm, ovoid in shape with acoustic enhancement posteriorly. Internal echoes and septations are common; rarely will the mass appear hyperechoic. The uterus appears normal. 5. Tubo-ovarian abscess involves a large portion of the pelvis. A large mass with disorganized heterogeneous echo pattern with solid and/or cystic areas will be seen.

Endometrium and Endometrial Cavity
As a review, the endometrium consists of two layers: functionalis, which is shed at the time of menstruation and the basalis, which restores the endometrium to prepare it for implantation. The phases of the endometrium start with menstruation. In this phase the coiled arteries constrict, reducing the supply of oxygen to the functionalis layer, shutting down the glands and the area becomes necrotic. The coiled arteries then rupture and bleeding ensues. On day 4 and 5, the basalis cells began to proliferate, to restore the epithelium for the next cycle. The proliferative phase correlates with days 4-14. In this phase the glands and connective tissue are regenerated by proliferation from the base. The functionalis has been fully restored by day 14, ending the follicular phase in a 28-day cycle. However, in longer cycles the proliferative phase is the one that is prolonged, so a 35-day cycle has a 20-21 day phase. Finally the secretory phase kicks in, which is the most constant phase in terms of time. In a 28-day cycle, the secretory phase starts on day 15 and lasts till day 28. A longer cycle can vary in the proliferative phase, delaying ovulation, however there is a constant lifetime for the corpus luteum.

The endometrium changes in appearance sonographically throughout the cycle. After menstruation the endometrium is seen as a thin single line, in mid-cycle (~days 7-14) the endometrium appears trilaminar (three layers), and finally during the secretory phase, the endometrium appears thick with a homogeneous appearance. (Figures 10,11,and 12)

Figure 10 - Post menstruation

Figure 11 - Trilaminar appearance during proliferation

Abnormal bleeding is one of the most common reasons a woman of any age seeks gynecologic health care. The most worrisome cause of abnormal bleeding is endometrial carcinoma, however benign etiologies are far more prevalent. These benign causes of bleeding can include fibroids, polyps and endometrial atrophy.⁷ Ultrasound along with Saline Infused Sonohysterography (SIS) can help in the diagnosis of these causes. Assessing the placement of an IUD (Figure 13) and endometrial abnormalities associated with Tamoxifen therapy are other areas where ultrasound can be helpful.

Figure 13 - IUD's in the coronal plane

Endometrial Cavity
The endometrial cavity is best evaluated in conjunction with sonohysterography, also known as saline infused sonohysterography (SIS). This procedure involves the installation of normal saline into the uterine cavity, which in turn expands the cavity and acts as a negative contrast medium.⁸ With the advent of three-dimensional imaging, volumes of the uterine cavity can be acquired and manipulated, enabling the best visualization of any mass within the cavity. Uterine synechiae/adhesions, polyps, submucosal fibroids and uterine anomalies can all be better evaluated with the use of saline enhanced sonohysterography and three-dimensional ultrasound.

Synechiae/adhesions (Figure 14) can show as a single or multiple bands running through the cavity on SIS.

Figure 14 - Uterine Adhesions (arrow)

Polyps
After menstrual sloughing, the endometrial lining grows rapidly under the influence of hormones such as estrogen. Polyps are areas of endometrium that grow a little too much. As they grow, they usually fan out but remain attached to a small stalk. Polyps are usually about the size of a pencil eraser, although they can be smaller and rarely, polyps can grow to the size of an orange. Since most polyps are small, they quite often do not cause symptoms. However, when symptoms do occur, they usually include excessive bleeding during a period, bleeding in between periods, or even spotting after intercourse. Polyps cause these symptoms because they dangle from their stalks and irritate the surrounding tissue, which causes the tissue to rub off, exposing tiny blood vessels, which in turn bleed. Sonohysterograms are used to help in the diagnosis of uterine polyps (Figure 15). Polyps are almost always hyperechoic on ultrasound as compared to the myometrium, sometimes with cystic areas, and may have a feeder blood vessel. Because they are actually endometrial tissue, polyps can be hard to distinguish from the endometrium without performing SIS. (Figure 16)

The three-dimensional images of the uterus obtained for this tutorial, were generated on a GE Healthcare Voluson 730 using a high frequency rotational endovaginal probe starting with the transducer in a mid-sagittal plane of the uterus. When the volume probe is activated, the acoustic array automatically sweeps through an operator-selected region of interest with no movement of the transducer. The acquired stored volumes can be manipulated on the Voluson system itself, or with offline software (4D-View) immediately or at a later point in time. Orientations of the uterus and adnexa other than the original scan plane can then be reviewed. One of the unique features on the GE Healthcare Voluson 730 using the endovaginal transducer is Beta-View (b-view). Using this tool the user is able to rotate the acoustic array from an end-fire position 45 degree in either direction. This allows for less movement of the transducer and a greater imaging area. This can be especially helpful when scanning ovaries lying further out in the adnexa, and for those patients who are in pain or very sensitive.

The advent of three-dimensional (3D) ultrasound is one of the most important advances in gynecological ultrasound recently. The ability to view the uterus and endometrium in virtually any plane, has added greater diagnostic confidence to ultrasound imaging. 3D ultrasound does not replace 2D ultrasound but, rather, complements it.

There are different types of 3D acquisition, manual, sensor-based and automatic. For manual acquisitions the user moves the probe during the data acquisition. The smoothness and speed at which the probe is moved should be constant. Since the time for post-processing depends on the acquired number of frames, it is recommended to start with a high frame rate. Low frame rates result in fewer acquired frames for the 3D dataset, which results in more intensive post-processing (interpolation). Manual acquisitions are much more user dependant and are unable to be used for measurement. When performing sensor-based acquisitions a transmitter is used to generate a pulsed electro-magnetic field, which is detected by a sensor attached to the transducer. As the sweep is done the position information is detected and used to calculate a 3D data set. Automatic acquisitions are more uniform and consistent due to the ultrasound system driving the movement of the acoustic array. The anatomy is acquired as a dataset and each anatomical scan plane can be rotated on the X, Y or Z-axis to obtain the optimal image, allowing for more accurate 2D and volume measurements.

The multiplanar display enables the user to view the uterus or adnexa in sagittal, axial, and reconstructed coronal planes simultaneously. The coronal plane can be especially helpful when diagnosing congenital uterine anomalies as it demonstrates the best view of the shape of the uterus and endometrium along with the relationship of the cornua to the cervix. The ability to pan through the dataset enables the user to measure or image any area of the uterus and view that area in three perpendicular planes simultaneously. Additionally adding rendering to the multiplanar view allows for the display of the surface of organs, such as the endometrium. Obtaining accurate volumes of the endometrium or entire uterus is also possible using the 3D images.

Some of the image enhancement tools available include compound resolution imaging, speckle reduction imaging, coded harmonic imaging, VCI (volume contrast imaging) and auto tissue optimization, which all can add to diagnostic confidence. (Figure 17)

Compound resolution imaging not only sends the ultrasound beam perpendicular to the acoustic window, but also in oblique directions. Several pulses from multiple angles are correlated to form one image line, which in turn gives better contrast resolution and clearer borders. Speckle reduction imaging SRI is an adaptive algorithm to reduce the unwanted effects of speckle in the ultrasound image, creating a more tissue-like image. Volume contrast imaging is a volume acquisition combined with rendering options. In other words, VCI is a thick-slice imaging technique that utilizes 4D probes to acquire a slice of tissue continuously and rapidly. This leads to better contrast enhancement and speckle suppression in the two-dimensional image.

Coded harmonic imaging diminishes low frequency high amplitude noise and improves imaging technically difficult patients. Coded Harmonics may be especially beneficial when imaging isoechoic lesions in shallow-depth anatomy in the breast, liver, and hard-to-visualize fetal anatomy. Auto tissue optimization automatically adjusts the dynamic range setting in B-mode and spectral Doppler mode. This function allows the examiner to instantly change between the standard user programs and a more contrast-enhanced image.

A	B	C
Figure 17 - A shows standard 2D image of an Ovary, B Shows the same image with SRI applied, and C shows the same image with SRI and CRI applied. Note the change in border definition.

• Ptrozza JC, Gray MR, Davis AJ, Reindollar RH. Congenital absence of the uterus and vagina is not commonly transmitted as a dominant genetic trait: outcomes of surrogate pregnancies. Fertil Steril. 1997;67:387-389.
• Pui MH. Imaging diagnosis of congenital uterine malformation. Comput Med Imaging Graph. 2004;28:425-433
• Essentials of Obstetrics and Gynecology; Hacker, Moore, Gambone (2004 Saunders/Elsevier)
• Ultrasonography in Obstetrics and Gynecology by Peter W. Callen (2000 Saunders/Elsevier)