Ovarian Mass

• Describe normal ovarian anatomy and function.

• Describe the sonographic features of benign ovarian masses.

• Describe the sonographic features of malignant ovarian masses.

• Identify factors useful in differentiation of ovarian masses.

CLINICAL SCENARIO

A 21-year-old woman who is 10 weeks pregnant presents to the emergency department with acute pelvic pain. The physician palpates a pelvic mass adjacent to the uterus and orders a pelvic sonogram. Transabdominal sonography of the uterus reveals a viable 10-week gestation with no evidence of subchorionic hemorrhage. Gray-scale, pulsed, and color Doppler imaging of the adnexa reveal the findings in Figure 17-1 (see Color Plate 12). What is the most likely diagnosis for these findings?

FIGURE 17-1 **(A),** Longitudinal sonogram of right ovary measuring 11.7 cm × 6.0 cm. **(B),** Doppler imaging of right ovary. **(C),** Longitudinal view of left ovary *(arrow)* measuring 4.4 cm × 2.2 cm.

Pelvic sonography plays an important role in the detection and evaluation of ovarian masses. Although many ovarian masses are found incidentally, indications that may prompt a sonographic evaluation to assess for an ovarian mass include pelvic pain, pelvic fullness, palpable mass, or a family history of ovarian or breast cancer.

Ovarian cancer usually produces nonspecific symptoms. In more than 70% of patients, malignant ovarian disease is diagnosed during the later stages, which significantly reduces the survival rate.¹ Although early detection may improve survival, reliable ovarian cancer screening for the general population has not yet been developed. The most widely used serum tumor marker for epithelial ovarian cancer is cancer antigen 125 (CA 125). If a woman’s serum concentration of CA 125 is elevated, transvaginal sonography may be performed to assess for an ovarian mass. Only 50% to 60% of women with stage 1 epithelial ovarian cancer have elevated serum levels, and other benign conditions can elevate serum concentrations of CA 125 as well.² The resultant low sensitivity and specificity limit the value of this test in detecting ovarian cancer. A combination of CA 125 testing with transvaginal sonography is sometimes performed as a screening method in women at high risk of having ovarian cancer.²

Despite the poor prognosis in most patients diagnosed with ovarian cancer, the lack of complete understanding of the pathogenesis of ovarian cancer, the increasingly recognized occurrence of interval cancers (cancers detected within a year after a negative screening test), and the high proportion of ovarian masses that are benign all make screening difficult. Multicenter trials are ongoing, and the results of these trials should provide useful information to determine whether screening is beneficial. Screening is not recommended for the general population at the present time.³ Women with a higher risk because of family history or known BRCA1 or BRCA2 (breast cancer gene) mutations may request sonographic screening, but even in these women, no benefit from screening has yet been shown.³

A variety of ovarian masses are examined in this chapter, including benign and malignant masses. Specific sonographic features of the mass can usually help determine the most likely diagnosis or significantly narrow the list of likely diagnoses, and this helps in determining treatment options. Although only pathology after surgical removal can determine the diagnosis with certainty, a sonographic diagnosis of an ovarian mass can often be strongly suggested based on morphologic features, Doppler findings, clinical signs and symptoms, and the age of the patient. To understand better how all of these factors contribute to a differential diagnosis, it is helpful to review ovarian anatomy and physiology and key sonographic observations to be made when evaluating ovarian masses.

Normal Ovarian Anatomy and Physiology

Anatomy

The ovaries are almond-shaped intraperitoneal endocrine organs that are composed of cortical and medullary tissue covered by epithelium. The ovarian cortex is the site of follicular development, and the medulla is the vascular core of the ovary. The ovary is supplied with blood from two sources: the ovarian artery arising from the aorta and the ovarian branch of the uterine artery.

Although the ovaries are attached to the uterus by the ovarian ligament and to the infundibulum of the fallopian tube and pelvic side wall by the suspensory ligament, the ovaries are relatively mobile organs that typically reside in the adnexa anterior to the internal iliac vessels and medial to the external iliac vessels. Ovarian size varies with a woman’s menstrual status and age; mean ovarian volume is approximately 3.0 cm³ in premenarchal girls, 10 cm³ in menarchal women, and 6.0 cm³ in postmenopausal women.⁴

Ovarian follicles contain the oogonia, and the appearance of these follicles depends on the stage of their development. Multiple follicles begin maturation, but ultimately a single follicle called a dominant or graafian follicle matures until it reaches a size of 2.0 to 2.5 cm before ovulation causes it to rupture. After ovulation, the collapsed follicle transforms into a corpus luteum.

Physiology

Follicular development is influenced by follicle-stimulating hormone (FSH) and luteinizing hormone (LH), which are gonadotropins produced by the pituitary gland. FSH stimulates follicular development within the ovaries. As the follicle matures, it secretes estrogen, which stimulates endometrial growth and proliferation. Around day 14 of the menstrual cycle, increased levels of estrogen provide a negative feedback mechanism to the pituitary gland causing it to stop secreting FSH and begin production of LH. The follicular phase of the ovarian cycle refers to the events leading to ovulation.

Around day 14 of the menstrual cycle, a surge of LH stimulates ovulation. Continued LH production promotes development and maintenance of the corpus luteum, which promotes and maintains a secretory endometrium. The corpus luteum secretes estrogen and progesterone, which stimulate glandular changes within the endometrium necessary for supporting an early pregnancy. If pregnancy does not occur within approximately 9 days, LH production ceases, and the corpus luteum regresses into a structure known as the corpus albicans. Persistence of the corpus luteum may delay menstruation or cause abnormal bleeding from continued progesterone production. The postovulatory period is known as the luteal phase.

Normal Sonographic Appearance

The ovaries are homogeneous in texture, with an echogenicity similar to that of the uterus and hypoechoic to surrounding bowel (Fig. 17-2). Anechoic follicles may be seen in the ovarian periphery, and the vascular medulla may appear echogenic compared with the cortex. The dominant follicle typically reaches 2.0 to 2.5 cm in size; however, it can reach 2.8 cm. Simple cysts seen within the ovary that measure less than 3.0 cm are assumed to be ovarian follicles.

FIGURE 17-2 Normal menarchal ovary containing several small follicles.

The corpus luteum forms from the ruptured dominant follicle, and luteinization is made possible by the development of numerous capillaries and a rich blood supply. Hemorrhage into the corpus luteum is very common, resulting in a hemorrhagic corpus luteum. The corpus luteum remains intact until about week 12 of a pregnancy or until day 23 of the menstrual cycle if pregnancy does not occur. The sonographic appearance of a corpus luteum is variable, but the corpus luteum is often irregular in shape with a thick wall that may be crenulated (Fig. 17-3, A and B). The corpus luteum is often highly vascular with abundant flow evident on color Doppler imaging (Fig. 17-3, C; see Color Plate 13). It is a normal structure and should not be misinterpreted as pathology.

FIGURE 17-3 **(A),** Corpus luteum *(asterisk)* with thick walls. **(B),** Corpus luteum *(asterisk)* with crenulated appearance. **(C),** Color Doppler image demonstrating flow around highly vascular corpus luteum.

After menopause, the ovaries atrophy and are frequently devoid of follicles, which make them difficult to identify. Postmenopausal women may occasionally have small cysts or residual follicles; generally, a simple cyst less than 1 cm can be ignored in postmenopausal women.⁵

Key Sonographic Observations

When an adnexal mass is discovered during sonographic evaluation, the location, echotexture, size of the mass, and any associated findings such as ascites should be documented. Determining whether a mass is cystic, solid, or complex (a nonspecific term generally used to denote a combination of cystic and solid components) requires observation of the following: acoustic enhancement or attenuation, the presence of internal echoes by optimized gain and frequency, loculation, thickness and regularity of any septations, and whether solid components represent tissue versus blood or debris, which can be determined by applying color or power Doppler imaging. One also needs to consider nonovarian causes for findings such as tuboovarian abscess, pyosalpinx or hydrosalpinx (see Chapter 15), ectopic pregnancy (see Chapter 21), or pedunculated fibroid (see Chapter 13).

Besides the sonographic findings, the patient’s age, menstrual status, symptoms, and family history need to be considered. Women in their reproductive years are much more likely to present with benign ovarian pathology, whereas postmenopausal women and women of reproductive age with a family history of ovarian or breast cancer are at higher risk for malignant ovarian pathology. Most ovarian masses found sonographically are benign. A complex-appearing ovarian mass in a woman during her reproductive years usually represents a hemorrhagic physiologic cyst, whereas a solid adnexal mass is more likely to be a pedunculated fibroid than a malignant ovarian tumor. However, a complex-appearing ovarian mass in a postmenopausal woman is more worrisome for ovarian malignancy. Many appearances can result in a complex adnexal mass, and it is important to identify specific sonographic features that the physician can use to make a likely diagnosis.

Many benign ovarian masses do not demonstrate sonographic evidence of vascularity in the internal components by Doppler imaging. Color Doppler imaging demonstrates peripheral flow around a simple cyst, a hemorrhagic cyst, an endometrioma, or cystic teratoma, but vascularity is not evident within the internal components. When the solid-appearing components of an ovarian mass demonstrate vascularity on color Doppler imaging, a benign or malignant neoplastic process must be considered. Table 17-1 presents sonographic characteristics associated with benign and malignant ovarian masses.

TABLE 17-1

Benign and Malignant Characteristics of Ovarian Masses

Benign Characteristics	Malignant Characteristics
Purely cystic	Complex with thick septations
Findings consistent with hemorrhagic cyst, endometrioma, or cystic teratoma	Complex with mural nodules or other solid areas not typical of a dermoid
No internal flow by Doppler imaging	Ascites (more than normal small amount often seen in premenopausal women)
Complex mass is thin walled, has thin septations, no papillary projections or other solid areas	Solid components of mass demonstrate vascularity on color Doppler imaging
Benign solid masses tend to demonstrate mild to no vascularity

The sonographic appearance of adnexal masses can occasionally be confusing. Hemorrhage can make a cystic mass appear complex or solid, whereas a solid mass may produce attenuation that obscures the borders of the mass. There are well-established findings associated with ovarian masses that make it possible to offer a differential diagnosis based on the patient’s clinical history and the sonographic appearance of the mass. For indeterminant masses, other imaging modalities such as magnetic resonance imaging (MRI) may be used.

Functional or Physiologic Ovarian Cysts

If an ovarian follicle or corpus luteum fails to regress, it can continue to fill with fluid and result in a functional or physiologic cyst. The term “functional cyst” means that the cyst is ovarian in origin and responds to cyclic hormonal changes. The functional ovarian cysts discussed in this chapter are follicular cysts and hemorrhagic cysts. Theca lutein cysts are functional cysts related to human chorionic gonadotropin exposure and are discussed in Chapter 16.

Sonographic Findings

Hemorrhage within the cyst creates predictable patterns described as the “fishnet” or reticular pattern (Fig. 17-5, A) or retracting clot (Fig. 17-5, B). Hemorrhagic cysts may also demonstrate internal echoes with a fluid/fluid level (Fig. 17-5, C). Sometimes a hemorrhagic cyst has a predominantly solid appearance, but color Doppler sonography demonstrates no blood flow within the cyst and may show a highly vascular rim around the periphery of the cyst (Fig. 17-6; see Color Plate 14).

FIGURE 17-5 Patterns of hemorrhage typically seen within a hemorrhagic cyst. **(A),** Reticular pattern. **(B),** Retracting clot *(arrow)*. **(C),** Hemorrhagic cyst demonstrating low-level echoes and fluid/fluid level *(arrow)*.

Nonfunctional Cysts

Nonfunctional cysts generally refer to cysts that do not respond to cyclic hormonal stimulation. These include cysts of ovarian origin, such as endometriomas, and cysts not of ovarian origin, such as paraovarian cysts and peritoneal inclusion cysts.

Paraovarian Cyst

Paraovarian cysts originate from the wolffian structures located in the broad ligament. They occur in women of all ages but are most often found in menstruating women. They are benign and typically asymptomatic, but larger cysts may cause symptoms. Paraovarian cysts vary in size, with larger cysts at an increased risk for the same complications as other cysts, such as torsion, hemorrhage, or rupture.

Sonographic Findings

Most paraovarian cysts appear as a small, simple cyst separate from the ovary (Fig. 17-7). If the cyst is close to the ovary, it may be difficult to differentiate it from a follicular cyst. Application of gentle hand or transducer pressure may help separate the cystic structure from the ovary. Because there is no rim of ovarian tissue, large paraovarian cysts may resemble the urinary bladder. Differentiation from the bladder can be made by having the patient void. Because paraovarian cysts do not respond to the hormone cycle, follow-up examination is likely to demonstrate little or no change in size and appearance.

FIGURE 17-7 Paraovarian cyst (calipers) shown adjacent to ovary.

Peritoneal Inclusion Cyst

Patients who have experienced abdominal surgery, trauma, pelvic inflammatory disease, or endometriosis may develop peritoneal adhesions. Peritoneal inclusion cysts result when adhesions surround an ovary, and the follicular fluid that normally escapes into the peritoneum accumulates within the confines of the surrounding adhesions. Pain and a pelvic mass are the most common clinical presentations. Treatment is usually conservative, with fluid aspiration or administration of oral contraceptives to limit ovarian activity.

Sonographic Findings

Peritoneal inclusion cysts appear as a multiloculated cystic mass either adjacent to or surrounding an ovary (Fig. 17-8). The ovary may be in the center of the septations and fluid or peripherally located. The fluid is usually anechoic, but echoes may be evident if hemorrhage or protein is present.