title: The natural history of simple renal cysts.
abstract: OBJECTIVE
  Although simple renal cysts are common in older patients, little is known concerning their natural history. We examined the natural history of renal cysts by investigating the prevalence and sequential changes in their size and number in individuals.
  
  
  METHODS
  We collected data on 14,314 individuals who participated in a multiphasic health screening program at our institute in 1999. An ultrasound renal cyst prevalence survey was performed. As a longitudinal study, 45 patients with renal cysts were followed a mean of 6 years from January 1993 to December 1999.
  
  
  RESULTS
  In the prevalence survey 1,700 individuals (11.9%) had at least 1 renal cyst on ultrasound. The ratio of men-to-women with cysts was 2:1. The prevalence of renal cysts increased more than 7-fold with age from 5.1% in the fourth to 36.1% in the eighth decade of life. Our longitudinal study revealed that the majority of cysts increased in size and number. The average increase in size and the rate of enlargement were 2.82 mm. and 6.3% yearly, respectively. Cysts in patients younger than 50 years grew more rapidly than those in patients 50 years old and older, at a rate of 3.94 and 1.84 mm. yearly, respectively (p = 0.010). Multiloculated cysts progressed more rapidly than simple cysts (6.93 versus 2.18 mm. yearly, p <0.0001).
  
  
  CONCLUSIONS
  The prevalence of renal cysts increases with age and shows a remarkable difference in incidence by sex. Renal cysts progress in size and number, and appear to grow more rapidly in younger patients. The natural history of multiloculated cysts may be distinct from that of simple cysts and warrants further investigation.
authors.affiliation: Department of Urology, Kurashiki Central Hospital, Kurashiki, Japan.
authors.forename: Naoki
authors.initials: N
authors.lastname: Terada
authors.forename: Kentaro
authors.initials: K
authors.lastname: Ichioka
authors.forename: Yosuke
authors.initials: Y
authors.lastname: Matsuta
authors.forename: Kazutoshi
authors.initials: K
authors.lastname: Okubo
authors.forename: Koji
authors.initials: K
authors.lastname: Yoshimura
authors.forename: Yoichi
authors.initials: Y
authors.lastname: Arai
mesh_terms: D000293:Adolescent; D000328:Adult; D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D005260:Female; D006801:Humans; D007564:Japan / Q000453:epidemiology; D052177:Kidney Diseases, Cystic / Q000000981:diagnostic imaging / Q000453:epidemiology / Q000503:physiopathology*; D008137:Longitudinal Studies; D008297:Male; D008875:Middle Aged; D009098:Multiphasic Screening; D015995:Prevalence; D012737:Sex Factors; D014463:Ultrasonography