title: Bosniak Classification for Complex Renal Cysts Reevaluated: A Systematic Review.
abstract: We systematically evaluated the Bosniak classification system with malignancy rates of each Bosniak category, and assessed the effectiveness related to surgical treatment and oncologic outcome based on recurrence and/or metastasis.
  
  
  
  In a systematic review according to PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) statement and the QUADAS-2 (Quality Assessment of Diagnostic Accuracy Studies) criteria, we selected 39 publications for inclusion in this analysis and categorized them into 1) surgical cohorts-all cysts treated surgically and 2) radiological cohorts-cysts with surgical treatment or radiological followup.
  
  
  
  A total of 3,036 complex renal cysts were categorized into Bosniak II, IIF, III and IV. In surgical and radiological cohorts pooled estimates showed a malignancy prevalence of 0.51 (0.44, 0.58) in Bosniak III and 0.89 (0.83, 0.92) in Bosniak IV cysts, respectively. Stable Bosniak IIF cysts showed a malignancy rate of less than 1% during radiological followup (surveillance). Bosniak IIF cysts, which showed reclassification to the Bosniak III/IV category during radiological followup (12%), showed malignancy in 85%, comparable to Bosniak IV cysts. The estimated surgical number needed to treat to avoid metastatic disease of Bosniak III and IV cysts was 140 and 40, respectively.
  
  
  
  The effectiveness of the Bosniak classification system for complex renal cysts was high in categories II, IIF and IV, but low in category III, and 49% of Bosniak III cysts was overtreated because of a benign outcome. This surgical overtreatment combined with the excellent outcome for Bosniak III cysts may suggest that surveillance is a rational alternative to surgery. This will require further study to assess whether surveillance of Bosniak III cysts will prove safe.
authors.affiliation: Department of Radiology and Nuclear Medicine, Erasmus MC - University Medical Center Rotterdam, Rotterdam, the Netherlands. Electronic address: i.schoots@erasmusmc.nl.
authors.forename: Ivo G
authors.initials: IG
authors.lastname: Schoots
authors.affiliation: Department of Urology, Erasmus MC - University Medical Center Rotterdam, Rotterdam, the Netherlands.
authors.forename: Keren
authors.initials: K
authors.lastname: Zaccai
authors.affiliation: Department of Radiology and Nuclear Medicine, Erasmus MC - University Medical Center Rotterdam, Rotterdam, the Netherlands; Department of Epidemiology, Erasmus MC - University Medical Center Rotterdam, Rotterdam, the Netherlands; Harvard School of Public Health, Harvard University, Department of Health Policy and Management, Boston, Massachusetts.
authors.forename: Myriam G
authors.initials: MG
authors.lastname: Hunink
authors.affiliation: Department of Urology, Erasmus MC - University Medical Center Rotterdam, Rotterdam, the Netherlands.
authors.forename: Paul C M S
authors.initials: PCMS
authors.lastname: Verhagen
mesh_terms: D003287:Contrast Media / Q000008:administration & dosage; D018450:Disease Progression; D006801:Humans; D007668:Kidney / Q000000981:diagnostic imaging / Q000473:pathology / Q000601:surgery; D052177:Kidney Diseases, Cystic / Q000000981:diagnostic imaging / Q000453:epidemiology* / Q000473:pathology / Q000517:prevention & control; D007680:Kidney Neoplasms / Q000145:classification* / Q000000981:diagnostic imaging / Q000453:epidemiology / Q000473:pathology; D009364:Neoplasm Recurrence, Local / Q000453:epidemiology* / Q000473:pathology / Q000517:prevention & control; D009392:Nephrectomy / Q000706:statistics & numerical data*; D015995:Prevalence; D014057:Tomography, X-Ray Computed / Q000379:methods; D016896:Treatment Outcome
chemical_list: D003287:Contrast Media
keywords: classification; cysts; kidney; numbers needed to treat; treatment outcome