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How long should we follow simple ovarian cysts with pelvic ultrasonography?

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A 54-year-old postmenopausal woman presents with a 3-day history of left lower quadrant pain. Abdominal and pelvic computed tomography confirm the diagnosis of acute diverticulitis, and a left ovarian cyst is incidentally noted. Her abdominal discomfort resolves with antibiotics.

Transvaginal ultrasonography confirms the presence of a 4.5-cm simple left ovarian cyst. The radiologist recommends follow-up ultrasonography in 3 months “if clinically indicated.” The patient feels well and is anxious about having additional testing. What do you recommend?

HOW USEFUL IS ULTRASONOGRAPHY FOR OVARIAN CYSTS?

Ovarian cysts are common and may affect up to 20% of women at some time during their life.1 In a prospective study of almost 40,000 women enrolled in an ovarian cancer screening program, the prevalence of ovarian cysts was 15.3% in premenopausal women and 8.2% in postmenopausal women.2

Pelvic ultrasonography is the most effective way to evaluate incidentally noted cysts, and the transvaginal approach is preferred.3 The International Ovarian Tumor Analysis group has outlined morphologic features, referred to as “simple rules,” for predicting if a cyst is malignant or benign.4 In a prospective validation study, these simple rules were applied in 76% of cases, with a sensitivity of 95% and a specificity of 91%.4 However, it should be noted that these rules apply to examinations done by experienced gynecologic ultrasonographers, as accuracy of ultrasonography is both machine- and operator-dependent.

WHAT IS THE MALIGNANCY POTENTIAL OF A SIMPLE OVARIAN CYST?

A simple ovarian cyst is defined as an anechoic round or oval lesion, different from a unilocular cyst, which may contain septations, solid wall irregularities, or internal echoes.5 Overall, simple ovarian cysts have a very low likelihood of malignancy. In the large, multi-site Prostate, Lung, Colorectal, and Ovarian Cancer Screening Trial, simple cysts were observed in 14% of postmenopausal women,6 but no cyst was associated with the development of ovarian cancer over 4 years of follow-up.

HOW OFTEN SHOULD IMAGING BE REPEATED?

In premenopausal women, most simple (thin-walled) ovarian cysts less than 5 cm in maximum diameter resolve in 2 to 3 menstrual cycles and do not require further intervention.3 Larger cysts (5–7 cm in diameter) should be followed with ultrasonography yearly. Cysts larger than 7 cm require advanced imaging or surgical intervention, and the patient should be referred to a gynecologist.3

In postmenopausal women, serum markers are combined with ultrasonography results to determine the risk of malignancy. Markers studied include cancer antigen 125 (CA-125), human epididymis protein 4, lactate dehydrogenase, alpha fetoprotein, and beta human chorionic gonadotropin (beta hCG).7

CA-125, the most studied marker, is elevated in more than 90% of advanced-stage ovarian cancers, but in only 50% of patients wth early-stage cancer.1,8 However, CA-125 may be elevated in a variety of other settings, including benign gynecologic disorders (pelvic infection, fibroids, endometriosis, adenomyosis) and nongynecologic disorders (liver disease, pancreatitis, and diverticulitis). Thus, it is unreliable for distinguishing benign from malignant ovarian masses in premenopausal women.1,3

Current guidelines recommend routine measurement of CA-125 in the initial evaluation of all postmenopausal women with an ovarian mass.7,8

Using a cutoff of 30 IU/mL, CA-125 has a sensitivity of 81% and a specificity of 75% for ovarian malignancy. However, serial measurements may be more useful for assessing ovarian cancer risk, especially in the setting of rapidly rising values.1,3

The Risk for Malignancy Index (RMI), which categorizes a cyst’s risk for malignancy, can be calculated based on the patient’s menopausal status, ultrasonographic characteristics (1 point each for multilocular cyst, solid area, metastasis, ascites, and bilateral lesions), and serum CA-125 level. The RMI has a sensitivity of 78% and a specificity of 87% for predicting ovarian cancer.8

Postmenopausal women with an asymptomatic small cyst (< 5 cm), a normal CA-125 level, and an RMI < 200 can be followed conservatively, with repeat ultrasonography in 4 to 6 months. At that time, if the cyst has not grown and the CA-125 level is normal, expectant management can continue, with reassessment in 4 to 6 months. If imaging remains unchanged and the CA-125 is persistently normal, the patient may be discharged from follow-up.8

If at any time during the evaluation the calculated RMI is greater than 200, there is an increased risk for malignancy, and the patient should be referred to a gynecologic oncologist for advanced imaging.

An algorithm from the Royal College of Obstetricians and Gynaecologists for managing ovarian cysts in postmenopausal women is available at www.rcog.org.uk/globalassets/documents/guidelines/green-top-guidelines/gtg_34.pdf.8

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