Bosniak classification system of renal cystic masses

Dr Ian Bickle and A.Prof Frank Gaillard et al.

The Bosniak classification system of renal cystic masses divides renal cystic masses into five categories based on imaging characteristics on contrast-enhanced CT. It is helpful in predicting a risk of malignancy and suggesting either follow up or treatment.

Classification

Bosniak 1
  • simple cyst
    • imperceptible wall, rounded
    • work-up: nil
    • percentage malignant: ~0%
Bosniak 2
  • minimally complex
    • a few thin <1 mm septa or thin calcifications (thickness not measurable); non-enhancing high-attenuation (due to proteinaceous or haemorrhagic contents) renal lesions of less than 3 cm are also included in this category; these lesions are generally well marginated
    • work-up: nil
    • percentage malignant: ~0%
Bosniak 2F
  • minimally complex
    • increased number of septa, minimally thickened with nodular or thick calcifications
    • there may be perceived (but not measurable) enhancement of a hairline-thin smooth septa
    • hyperdense cyst >3 cm diameter, mostly intrarenal (less than 25% of wall visible); no enhancement
    • requiring follow-up: needs ultrasound/CT follow up - no strict rules on the time frame but reasonable at 6 months
    • percentage malignant: ~ 5% 6
Bosniak 3
  • indeterminate
    • thick, nodular multiple septa or wall with measurable enhancement, hyperdense on CT (see 2F)
    • treatment/work-up: partial nephrectomy or radiofrequency ablation in elderly or poor surgical candidates
    • percentage malignant: ~55% 6
Bosniak 4
  • clearly malignant
    • solid mass with a large cystic or a necrotic component
    • treatment: partial or total nephrectomy
    • percentage malignant: ~100%

History and etymology

It is named after Morton A. Bosniak 9

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Article information

rID: 1006
System: Urogenital
Tag: kidney
Synonyms or Alternate Spellings:
  • Bosniak classification system of renal cysts
  • Bosniak renal cyst classification system
  • Bosniak renal cyst classification
  • Bosniak classification system of renal cystic lesions

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Cases and figures

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    Figure 1
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    Case 1: Bosniak grade 1
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    Case 2: Bosniak grade 1
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    Case 3: Bosniak grade 2 - haemorrhagic cyst
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    Case 4: Bosniak grade 2
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    Case 5: Bosniak grade 2
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    Case 6: Bosniak grade 2
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    Case 7: Bosniak grade 3 - with enhancing mural nodule
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    Case 8: Bosniak grade 4
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    Case 9: Bosniak grade 4
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    Case 10: Bosniak grade 4
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    Case 11: Bosniak type 4 cyst on a background of APKD
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