Skilled US imaging of the adnexae: Ovarian Neoplasms

Although roughly three quarters of ovarian neoplasms occur in premenopausal women, 87% of masses in this population are benign. The vast majority of malignant neoplasms—about 75%—are diagnosed in postmenopausal women.

These figures suggest that you have some discerning to do. Specifically, how do you identify the small percentage of masses in premenopausal women that are malignant—and winnow out the benign neoplasms in the postmenopausal population?

Now that we’ve equipped you with an understanding of the morphologic building blocks of adnexal masses, and how those masses are assessed using ultrasonography (US) (described in Part 2 of this four-part series), you can apply your skills of discernment to ovarian neoplasms. Specifically:

• teratoma (dermoid cyst)—one of the two most prevalent benign neoplasms of the ovary
• serous cystadenoma—the other most prevalent benign neoplasm
• hormone-secreting tumors
• malignant neoplasms.

Recall that Part 1 of this series offered a starting point for US imaging of the adnexae by describing (and showing) how basic pelvic structures appear in grayscale US and color and power Doppler. Part 2 focused on non-neoplastic ovarian masses. Part 4 will take as its subject tubal entities such as torsion, ectopic pregnancy, and cancer.

Teratomas present a variety of “faces”

Teratomas may appear to be solid, cystic, or both (FIGURE 1). At times, they have a bizarre or variable appearance. The overwhelming majority of teratomas can be recognized by shadowing, which may be extreme if the tumor contains a solid, echogenic central mass (FIGURE 1A). Such an echogenic core is sometimes called the “fried egg” sign when it is detected by transabdominal US.

FIGURE 1 Cystic and solid benign teratomas

A. Shadowing (small arrows) is apparent in a teratoma containing low-level echoic fluid. B. Several spherical “balls” floating in a cystic teratoma, with shadowing. C. Solid teratoma. D. A “typical” teratoma, with septation and multilocularity. E. Macroscopic view of an ovarian teratoma (arrow). F. Multiple sebaceous ball-shaped structures within a benign cystic teratoma (inset: macroscopic view).When the teratoma is cystic or partially cystic, it may contain a linear hyperechoic area consistent with sebaceous fluid and hair. Although magnetic resonance imaging (MRI) can confirm the fat content of a teratoma, US is very efficient in making the diagnosis, rendering MRI unnecessary.

As for blood vessels, teratomas are known to have scant or no apparent vascularity. A rule of thumb: If a bizarre adnexal structure with no vascularity is visible on US, and if it is cystic or solid in appearance (or both), benign teratoma should be included in the differential diagnosis.

Because an ovarian teratoma can assume almost any shape and form, three-dimensional (3D) US is almost useless in its evaluation.

Cystadenomas are relatively easy to identify on US

Benign cystadenomas—serous or mucinous—are extremely common. In at least 20% to 30% of cases, they are bilateral.

The US characteristics of these masses include:

• multilocularity, in many cases (although two thirds of simple unilocular cysts in postmenopausal women are serous cystadenomas)
• multiseptation, with the septae often fanning out from a central, apparently solid structure (FIGURE 2)
• anechoic nature when they contain fluid (in the serous variety) or with low-level echogenicity (in mucous cystadenomas).

FIGURE 2 Benign cystadenoma

A–C. Typical sonographic appearance of a benign cystadenoma, with septae fanning out from a solid area, creating an anechoic, fluid-filled, multilocular pattern. D. MRI appearance of the cyst (arrow points to solid area from which the septae fan out).As for vascularity, cystadenomas have a paucity of core vessels and have, if measured quantitatively, what we consider to be normal resistive and pulsatility indices and low peak systolic velocity. Histologically, they are benign. These neoplasms can be identified using US with relative ease and high confidence, rendering computed tomography (CT) and MRI (FIGURE 2D) virtually redundant.

When US characteristics overlap

Based on our 20 years of experience with US assessment of adnexal masses, and the potential overlap (on grayscale as well as color and power Doppler) between the US appearance of endometriomas, cystadenomas, and cystic teratomas, we recommend that, when a mass is not pathognomonic on US, this triad of entities be considered in the differential diagnosis. The entity that has the greatest number of relevant characteristics should be listed as the most likely and first possibility on the US report.

(For a description of the US appearance of endometriomas, see Part 2 of this series, which appeared in the October 2010 issue of OBG Management.)