The 10-year natural history of simple renal cysts

OBJECTIVE We previously reported the natural history of renal cysts, with a mean follow-up of 6 years. Here, we extended the follow-up period to 10 years. METHODS From January 1993 to August 2006, 61 patients diagnosed with renal cysts were followed for up to 14 years (mean 9.9 years). The sequential changes in renal cyst size were plotted against patient age, and the rate of increase in cyst size per year was calculated for each individual. Those cyst characteristics known to predict aggressiveness were analyzed. RESULTS The majority of the cysts increased in size and number. The average size increase and the average rate of enlargement in all cysts were 1.6 mm and 3.9% per year, respectively. Several cysts, especially multiloculated cysts, increased rapidly during the first 2 to 3 years, but then the rate of growth tended to decelerate with time. By using univariate analyses, age, laterality and cyst shape were revealed to be significant predictors of aggressiveness. The multivariate analysis revealed that age was the most significant predictor. Renal neoplasms originating from the renal cysts appeared in 2 patients during the follow-up period. The rate of size increase of the neoplasm-bearing cysts was similar to that of the other benign renal cysts in the same age category. CONCLUSIONS The simple renal cysts continued to increase in size over 10 years, and sometimes increased rapidly, especially in younger patients. However, their growth rates appeared to decrease with age. There seems to be no specific pattern observed in the neoplasm-bearing renal cysts.