Bosniak classification of renal cysts

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Bosniak classification of renal cysts is a radiologic classification system for kidney cysts. It originally consisted of four categories (I, II, III, IV).[1][2]

A subsequent modification turned it into a five category system:

Category Percent malignant Management Radiological Characteristics
Bosniak I 0% no follow-up necessary Simple cyst
Bosniak II 0% no follow-up necessary Minimally complex (septa <1mm or thin calcification; non-enhancing attenuation due to proteinaceous or haemorrhagic contents)
Bosniak IIF 5% follow-up (4 years[3]) Minimally complex (increased septa, but minimally thicknened/nodular; perceived, but not measurable enhancement)
Bosniak III 50% excise to r/o malignancy Indeterminate (thick or nodular septa with measurable CT enhancement)
Bosniak IV 100% almost certainly malignant Clearly malignant (solid mass +/- cystic/necrotic component)


  • The "F" in IIF have minimally suspicious features and should get follow-up imaging.[4]


See also


  1. Bosniak, MA. (Jan 1986). "The current radiological approach to renal cysts.". Radiology 158 (1): 1-10. doi:10.1148/radiology.158.1.3510019. PMID 3510019.
  2. Curry, NS.; Cochran, ST.; Bissada, NK. (Aug 2000). "Cystic renal masses: accurate Bosniak classification requires adequate renal CT.". AJR Am J Roentgenol 175 (2): 339-42. doi:10.2214/ajr.175.2.1750339. PMID 10915671.
  3. Hindman, NM.; Hecht, EM.; Bosniak, MA. (Sep 2014). "Follow-up for Bosniak category 2F cystic renal lesions.". Radiology 272 (3): 757-66. doi:10.1148/radiol.14122908. PMID 24766033.
  4. Ding, Y.; Chen, L.; Deng, FM.; Melamed, J.; Fan, R.; Bonsib, S.; Zhou, M. (Apr 2013). "Localized cystic disease of the kidney: distinction from cystic neoplasms and hereditary polycystic diseases.". Am J Surg Pathol 37 (4): 506-13. doi:10.1097/PAS.0b013e318271eff9. PMID 23211292.
  5. Muglia, VF.; Westphalen, AC.. "Bosniak classification for complex renal cysts: history and critical analysis.". Radiol Bras 47 (6): 368-73. doi:10.1590/0100-3984.2013.1797. PMID 25741120.