Natural 10-year history of simple renal cysts

PURPOSE To carry out long-term follow-up of patients diagnosed with asymptomatic simple renal cysts (SRCs). MATERIALS AND METHODS One hundred fifty-eight adult patients in whom SRCs were incidentally diagnosed by abdominal ultrasonography or abdominopelvic computed tomography between August 1994 and June 2004 were followed up for over 10 years. The retrospective analysis investigated sequential changes in the size, shape, and Bosniak classification of the renal cyst and analyzed risk factors for increased size and growth rate of the cysts. RESULTS The median follow-up period was 13.9 years (range, 10.0-19.8 years). Median patient age was 54.1 years (range, 22-86 years). Mean maximal cyst size was 33 mm (range, 2-90 mm). Among all patients, 120 (76%) showed a mean increase in maximum renal cyst diameter of 1.4 mm (6.4%) per year. Age at initial diagnosis was a risk factor for increased renal cyst maximum diameter. The probability of an increase in maximum diameter of an SRC was 7.1 times greater in patients aged 50 years or older at diagnosis than in those aged less than 50 years. However, among patients with an increased maximum diameter, the mean growth rate was lower in patients aged ≥50 years than in those aged <50 years. CONCLUSIONS About three-quarters of adult patients with accidentally diagnosed SRCs presented with an increased maximum diameter. The only risk factor for an increase in maximum diameter was age. In patients with an increase in the maximum diameter, the growth rate of the maximum diameter was 6.4% per year during 10 years and decreased with age.