Bosniak Classification for Complex Renal Cysts Reevaluated: A Systematic Review

J Urol. 2017 Jul;198(1):12-21. doi: 10.1016/j.juro.2016.09.160. Epub 2017 Mar 9.


Purpose: 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.

Materials and methods: 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.

Results: 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.

Conclusions: 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.

Keywords: classification; cysts; kidney; numbers needed to treat; treatment outcome.

Publication types

  • Systematic Review

MeSH terms

  • Contrast Media / administration & dosage
  • Disease Progression
  • Humans
  • Kidney / diagnostic imaging
  • Kidney / pathology
  • Kidney / surgery
  • Kidney Diseases, Cystic / diagnostic imaging
  • Kidney Diseases, Cystic / epidemiology*
  • Kidney Diseases, Cystic / pathology
  • Kidney Diseases, Cystic / prevention & control
  • Kidney Neoplasms / classification*
  • Kidney Neoplasms / diagnostic imaging
  • Kidney Neoplasms / epidemiology
  • Kidney Neoplasms / pathology
  • Neoplasm Recurrence, Local / epidemiology*
  • Neoplasm Recurrence, Local / pathology
  • Neoplasm Recurrence, Local / prevention & control
  • Nephrectomy / statistics & numerical data*
  • Prevalence
  • Tomography, X-Ray Computed / methods
  • Treatment Outcome


  • Contrast Media