What are the most common benign lesions of the ovaries and their imaging characteristics?
The most common benign ovarian lesions include functional cysts and hemorrhagic cysts, which are typically diagnosed on transvaginal US. Functional cysts include follicular and corpus luteum cysts. A follicular cyst occurs when ovulation does not occur and the egg is not released due to lack of a luteinizing hormone (LH) surge. If ovulation occurs, a dominant follicle extrudes an egg and becomes a corpus luteum. If pregnancy occurs, the corpus luteum may fill with fluid or blood and becomes a corpus luteum cyst.
On US, a follicular cyst is identified as a unilocular anechoic ovoid or round lesion with posterior acoustic enhancement. A corpus luteum cyst is thick-walled and has increased vascularity with a classic “ring of fire” appearance on Doppler US. On MRI, functional ovarian cysts demonstrate homogenous hyperintense T2-weighted signal intensity similar to that of fluid and hypointense T1-weighted signal intensity with a thin wall.
Hemorrhagic cysts develop when there is hemorrhage within a functional cyst. US of a hemorrhagic cyst demonstrates mixed echogenicity and lacy interfaces due to the presence of blood products. On MRI, hemorrhagic cysts demonstrate varying imaging characteristics, with roughly two thirds appearing isointense or hypointense on T1-weighted images and one third appearing hyperintense. T2-weighted signal intensity is also variable.