The ovaries are paired ovoid pelvic organs located on each side of the uterus. They are mobile intraperitoneal structures that lie anterior to the retroperitoneal structures, such as the ureters and internal iliac vessels. Each ovary receives its blood supply from the ovarian artery, which arises from the aorta, as well as from branches of the uterine artery.

In women of reproductive age, two types of functional cysts may be found in the ovaries: follicular cysts and corpus luteal cysts. During the first half of the menstrual cycle, multiple follicles develop until one (or occasionally more) becomes dominant. The dominant follicle ruptures midcycle, at the time of ovulation, and involutes to become a corpus luteum. The corpus luteum regresses at the end of the menstrual cycle. Functional cysts are generally less than 2.5 cm in diameter but may become larger if they fail to involute or if they fill up with fluid or blood.

After menopause, the ovaries decrease in size, both because ovarian tissue atrophies and because ovarian cysts occur infrequently. When cysts occur in the postmenopausal ovary, they require follow-up or removal only if they are large or complex.

The ovaries are generally visualized better by transvaginal than transabdominal sonography. An exception is the ovary located high in the pelvis, which may only be seen transabdominally. The premenopausal ovary appears on ultrasound as a soft tissue structure with multiple small cysts, corresponding to functional cysts (Figure 28.1.1). If the scan is done at
a time when an ovary has a dominant follicle, one of the cysts will be considerably larger than the others (Figure 28.1.2). If the scan is done after the patient has ovulated, a corpus luteum will be present. The corpus luteum has a variable appearance, but the most typical is a complex cyst with an irregular, thick wall, and internal echoes. Abundant flow at the periphery of the corpus luteum, sometimes called a “ring of fire,” is characteristic of these physiologic cysts (Figure 28.1.3).