Sonography is the diagnostic modality of choice for the initial evaluation of most patients with a pelvic mass. This is particularly true for pelvic masses thought, on a clinical basis, to be benign. Although the sonographic features of a pelvic mass frequently do not permit a specific histopathologic diagnosis, sonography usually provides clinically important parameters for the pelvic mass.¹ These include the following:

1. 
   

   Confirmation of the presence or absence of a pelvic mass

   
   
2. 
   

   Delineation of its size, internal consistency, and contour

   
   
3. 
   

   Establishment of the origin and anatomic relationship of the mass to other pelvic structures

   
   
4. 
   

   A survey to establish the presence or absence of abnormalities associated with malignant disease, such as ascites or metastatic lesions

   
   
5. 
   

   Guidance for aspiration or biopsy of selected pelvic masses, such as tubo-ovarian abscesses

Each of these parameters will be discussed, as well as specific types of pelvic masses. This chapter is structured to emphasize the way sonographic evaluation of pelvic masses proceeds from evaluation of clinically pertinent parameters to consideration of specific lesions. It includes recently published guidelines for distinguishing benign versus malignant pelvic masses by the International Ovarian Tumor Analysis (IOTA) and guidelines for the follow-up of adnexal lesions by the Society of Radiologists in Ultrasound (SRU).^2,3

Information gained by sonography is useful in guiding the gynecologic surgeon through decisions regarding surgical intervention. In general, masses that are over 5 cm in average dimension, contain irregular solid components, or are associated with significant amounts (over 20 mL) of intraperitoneal fluid require surgical treatment.⁴ Similarly, pelvic masses that are associated with acute pelvic pain may require immediate surgical intervention because they may be associated with adnexal torsion.^5,6 In contrast, masses that are completely cystic and smaller than 4 to 5 cm may be observed over a few months with repeat sonograms to document any change in size. If the cystic mass is unilocular (<10 cm) it also can often be observed.⁷ Although small (<5 cm) unilocular cystic adnexal masses can be detected in postmenopuasal women, only a minority will represent a malignant neoplasm.⁴ However, since the postmenopausal ovary should not be larger than approximately 2 cm these small cystic masses that are greater than 1 cm do require follow-up ultrasound evaluation if surgical exploration is not performed. In patients with recurrent ovarian carcinoma, sonography has been found to be highly accurate in the detection of ascites, but it is a poor predictor of the presence of diffuse small peritoneal implants.⁸

The role of magnetic resonance imaging (MRI) and computed tomography (CT) relative to sonographic evaluation of pelvic masses must be considered. In general, CT and MRI are more accurate than sonography in staging histologically proven neoplastic tumors, such as cervical carcinoma.⁹ However, because of their high operational costs and limited availability, these modalities are not as frequently used in the initial evaluation of a pelvic mass as is sonography. CT and MRI are usually used as a secondary adjunctive examination when the characteristics of the mass raise concern about malignancy.

The use of transvaginal sonography (TVS) can add specificity in certain areas to the conventional transabdominal sonographic examination. The limited field of view of most transvaginal transducer/probes confines their use to the pelvis where global delineation of structures is of diagnostic importance; however, the added information regarding tumor composition and location can add specificity to the sonographic examination.

The role of color Doppler sonography (CDS) has evolved over the last decade or so. First thought to be diagnostic of neoplasms by special waveform analysis (neoplasms were thought to have low impedance flow). The CDS provides important information regarding the presence of flow within solid internal areas in masses.

CDS is also helpful in depicting the overall vascularity of a pelvic mass and its relationship to pelvic vascular landmarks such as the iliac vein. It is also helpful in the evaluation of adnexal torsion.¹⁰ TV-CDS is particularly useful as an adjunct to morphologic assessment of ovarian lesions.^10,11 TV- and TA-CDS can also depict vascularity within solid areas and demonstrate the relative arrangement and caliber of vessels. This topic is also discussed in detail in Chapter 36.

Three-dimensional US is also useful in the evaluation of the morphologic features (ie, wall irregularities) of a pelvic mass and in particular to confirm the diagnosis of a fluid filled distended tube (hydro- or pyosalpinx) or in distinguishing a paratubal or paraovarian mass from a tubal lesion. 3D-TV and TA CDS can also depict the relative vascularity within solid area and the relative arrangement of vessels and their caliber.

Accordingly, the aim of this chapter is to familiarize the reader with certain differential points that are clinically important when evaluating a patient with a pelvic mass via transabdominal, transvaginal grey scale and CDS, or both. The topic of early detection of ovarian cancer is covered in Chapter 36, and there is an entire chapter (Chapter 49) devoted to 3D US for the interested reader.

The Presence or Absence of a Pelvic Mass

Pelvic sonography has an important role in establishing the presence of a pelvic mass in patients where one is palpated or suspected on pelvic examination and in those who experience adnexal pain and/or tenderness. It is particularly useful in patients in whom an adequate pelvic examination cannot be performed or in whom a poorly defined pelvic mass is found on examination.

Because some masses may be outside the range of the examiner’s finger, sonography may occasionally detect masses that cannot be palpated adequately. In this situation, a real-time sonographic examination during pelvic examination may be used to demonstrate the presence or absence of a mass.¹² TVS can be used to particular advantage in the delineation of the uterus and ovaries in obese patients. In fact, sonography has been found to be more reliable than palpation in the identification of normal-sized ovaries, particularly in postmenopausal women.¹³

The change in configuration of bowel loops associated with peristalsis is helpful in distinguishing true pelvic masses from those created by bowel. A fecal-filled cecum may occasionally simulate the appearance of a solid adnexal mass, as may matted omentum or fat that is in the adnexal region. TVS may be helpful in these cases to distinguish true pelvic masses from those created by bowel.

Size and Location

The uterus serves as a central landmark for identifying the location of a mass within the pelvis (Figure 33-1). The echogenic endometrial interface within the uterus serves as an additional landmark for delineation of its borders.¹⁴ Masses within the ovary can usually be identified by the rim of compressed parenchyma (“beak”) that is present between the mass and the remaining portion of the ovary. This feature is particularly well depicted with transvaginal scanning. Abnormally distended tubes can be identified by their origin from the lateral aspect of the uterine cornu and their fusiform enlargement as they extend from the uterus into the pelvis. In addition, the origin of the tube can be identified on semiaxial or coronal transvaginal examinations by delineating the portion of the endometrium that extends into the cornu. Hydrosalpinges also typically demonstrate an “incomplete” septum interface in a septated adnexal mass and the presence of tiny intraluminal projections arising from endosalpingeal folds.

The size of the pelvic mass occasionally can be helpful in distinguishing its differential diagnosis. Physiologic cysts, for example, are rarely larger than between 3- and 5-cm average dimension; ovarian tumors have generally enlarged to about 10 cm before they are symptomatic. Exceptions to this may be encountered in acute hemorrhage or torsion of the ovary, when it can quickly enlarge over a 24- to 48-hour time period.

In some obese patients, it may be difficult to palpate some masses, even those that are larger than 10 cm.¹⁵ Size alone, however, is not a specific criterion to distinguish benign versus malignant pelvic masses because it depends on when the patient presents for an examination relative to the growth pattern of the mass.

The origin of a mass may be further elucidated by applying gentle pressure with the transvaginal probe and palpating hand between the mass and the uterus. For example, pedunculated subserosal fibroids can be identified by the presence of a pedicle attaching to the uterus, whereas an adnexal mass would be separable from the uterus. Similarly, the ability to appreciate a mass from a surrounding organ by this maneuver (“sliding organ sign”) may help distinguish an adnexal tubal ring of an ectopic from the adjacent ovary. Conversely, if the structure represents a corpus luteum, it can be appreciated to be contained within the ovary. The “sliding organ sign” can be used to detect masses that have significant adhesions since in these patients, an adnexal structure is not readily seen to be moving separate from the ovary.¹⁶ Infiltrative endometriosis can also be detected by the lack of ability to visualize separate motion of the bowel from the ovary or bladder wall for example. Those features which suggest fixation of structures involving infiltrative processes are discussed in more detail in the chapter devoted to TVS of acute and chronic pelvic pain (Chapter 37). These features are shown on the cineloops in the website associated with this textbook.

Internal Consistency

Sonography allows detailed delineation of the internal consistency of a pelvic mass (Figures 33-2, 33-3, 33-4, 33-5, 33-6). A cystic mass can be inferred when the mass has no internal echoes, smooth borders, and has enhanced through transmission.¹⁷ Three-dimensional volumetric imaging of the inner wall of a simple cyst can be distinguished from those with papillary excrescences. Occasionally, low-level echoes may be present within a cyst arising from proteinaceous fluid, blood, or cellular debris. A truly solid mass typically contains internal echoes, whereas a complex mass contains both solid and cystic components. Color Doppler assessment of solid internal components helps distinguish a formed clot, without typical flow from a neoplastic solid mass that typically demonstrates internal flow.