LAUSR

Background We conducted a multi-center study to investigate the prevalence, the malignant transformation potential of the simple renal cysts and the factors that might predict malignancy. Methods We defined the simple renal cysts as Bosniak class I & II (including IIF) lesions. In the prevalence study, data from 115,132 ultrasonographies was collected from individuals who participated in a multiphasic health wellness screen. In the natural history and progression study, we retrospectively reviewed 333 participants with simple renal cysts and were followed for at the least 3 years with a mean of 6.3±2.9 years (ranged from 3 to 13 years). Results About 7.2% (8,303) of the individuals who participated in the study were found to have at the least one simple renal cyst. The incidence increased with age from 0.6% in the first decade to 28.0% in the eighth or later decade of life. The Bosniak class I lesion accounted for 7,559 or 91.0% of the cysts whereas 744 or 9.0% were class II. A slower growth rate was observed in the older age group. Twenty-four patients (7.2%) had their renal cysts upgraded according to the Bosniak classification. Gender, age, initial cyst size, number of cysts and bi-laterality failed to predict the malignancy tendency. Conclusions Most of the cysts discovered were the Bosniak class I and II lesions and they rarely progress further. Treatment for the asymptomatic simple renal cyst is not warranted. Treatment decision-making based on older age or larger initial cyst size should not be recommended.