Objective: To determine the natural history and to estimate the risk of malignancy of unilocular ovarian cystic tumors less than 10 cm in diameter followed conservatively by transvaginal ultrasound.
Methods: From 1987 to 2002, 15,106 asymptomatic women at least 50 years old entered the University of Kentucky's Ovarian Cancer Screening Program and underwent initial transvaginal ultrasonography. If the screen revealed nothing abnormal, women were asked to repeat transvaginal ultrasonography yearly. If the screen revealed abnormalities, transvaginal ultrasonography was repeated in 4 to 6 weeks, along with Doppler flow ultrasonography and CA 125 testing.
Results: Of the 15,106 women at least 50 years old, 2763 women (18%) were diagnosed with 3259 unilocular ovarian cysts. A total of 2261 (69.4%) of these cysts resolved spontaneously, 537 (16.5%) developed a septum, 189 (5.8%) developed a solid area, and 220 (6.8%) persisted as a unilocular lesion. During this time, 27 women received a diagnosis of ovarian cancer, and ten had been previously diagnosed with simple ovarian cysts. All ten of these women, however, developed another morphologic abnormality, experienced resolution of the cyst before developing cancer, or developed cancer in the contralateral ovary. No woman with an isolated unilocular cystic ovarian tumor has developed ovarian cancer in this population.
Conclusion: The risk of malignancy in unilocular ovarian cystic tumors less than 10 cm in diameter in women 50 years old or older is extremely low. The majority will resolve spontaneously and can be followed conservatively with serial transvaginal ultrasonography.