Bosniak Classification of Renal Cystic Masses

Based on findings on CT and MRI, per the revised 2019 guidelines

Bosniak MAIN
What imaging modality do you want to report for?
What is the scan's protocol?
Which one best describes the lesion?
Which one best describes the lesion?
Does the lesion have imaging features of a solid mass?
Does the lesion have any enhancing nodule(s)*?
*Enhancing Nodule: ≥4 mm convex protrusion with obtuse margins, or a convex protrusion of any size that has acute margins
What kind of septa does the lesion have?
How are the lesion's walls?
How is the lesion's attenuation?
Does the lesion have any calcifications?

Bosniak classification does not apply to this lesion.

Recommendation: Renal mass CT or MRI

Bosniak classification does not apply to renal masses.

Recommendation: Renal mass MRI

Bosniak II

Recommendation: No follow-up is needed

Bosniak IV

Recommendation: Urology consult

Bosniak III

Recommendation: Urology Consult

Bosniak II

Recommendation: No follow-up

Bosniak IIF

Recommendation: Re-image every six months twice, then every one year for four times (total follow-up of 5 years)

Bosniak I

Recommendation:
No follow-up
What is the scan's protocol?
Which one best describes the lesion?
Does the lesion have any of the following features?
Does the lesion have any enhancing nodule(s)*?
*Enhancing Nodule: ≥4 mm convex protrusion with obtuse margins, or a convex protrusion of any size that has acute margins
What kind of septa does the lesion have?
How are the lesion's walls?
Is the lesion nonenhancing and heterogenously hyperintense at T1w fat sat imaging?
Is the lesion's intensity homogenous and similar to CSF on T2w imaging?
Does the lesion have any calcifications?

Bosniak classification does not apply to this lesion.

Recommendation: Renal mass CT or MRI

Bosniak classification does not apply to renal masses.

Bosniak II

Recommendation: No follow-up is needed

Bosniak IV

Recommendation: Urology consult

Bosniak III

Recommendation: Urology Consult

Bosniak II

Recommendation: No follow-up

Bosniak IIF

Recommendation: Re-image every six months twice, then every one year for four times (total follow-up of 5 years)

Bosniak I

Recommendation:
No follow-up

References:
  1. Warren KS, McFarlane J. The Bosniak classification of renal cystic masses. BJU Int. 2005;95(7):939-942. doi:10.1111/j.1464-410X.2005.05442.x
  2. Silverman SG, Pedrosa I, Ellis JH, et al. Bosniak Classification of Cystic Renal Masses, Version 2019: An Update Proposal and Needs Assessment. Radiology. 2019;292(2):475-488. doi:10.1148/radiol.2019182646
More about this calculator:

This calculator utilizes the Bosniak classification of cystic renal masses (2019 version) to assist healthcare professionals in evaluating and categorizing renal cysts based on imaging findings. The Bosniak classification v2019 introduces updated criteria to improve the specificity and inter-reader agreement in assessing renal masses, making it an essential tool for radiologists and urologists alike.

Bosniak Classification of Renal Masses Calculator

Purpose: To facilitate the evaluation of cystic renal masses using the Bosniak classification system, providing a structured approach to determine the likelihood of malignancy.

Classification Criteria (2019 Revision):

  • Class I:
    • Well-defined thin (≤2 mm) smooth wall
    • Homogeneous simple fluid (CT: -9 to 20 HU; MRI: similar to CSF)
    • No septa or calcification
    • Wall may enhance after contrast administration
  • Class II:
    • Thin (≤2 mm) smooth walls with few (1-3) septa
    • Septa and wall may enhance
    • May have calcifications of any type
    • Homogeneous masses with varying attenuation/signal intensity (CT: ≥70 HU, 21-30 HU; MRI: markedly hyperintense on T1W/T2W)
  • Class IIF:
    • Smooth minimally thickened (3 mm) enhancing wall
    • Many (≥4) smooth thin (≤2 mm) enhancing septa
  • Class III:
    • One or more enhancing thick (≥4 mm) or irregular septa
    • Convex protrusion(s) with obtuse margins
  • Class IV:
    • One or more enhancing nodule(s)
    • Convex protrusion ≥4 mm with obtuse margins
    • Any size protrusion with acute margins
How to Use the Calculator
  1. Select the Imaging Modality: Choose between CT or MRI criteria based on the available imaging studies.
  2. Input Imaging Findings: Enter the details from the imaging studies, such as wall thickness, septa presence, and enhancement characteristics.
  3. Calculate the Class: The calculator will process the input data according to the Bosniak classification v2019 and provide a class assignment.
  4. Clinical Application: Use the calculated class to guide management strategies, including surveillance or surgical consultation, and facilitate communication within the care team.
Important Notes

This calculator is based on the Bosniak classification v2019, which is intended for general patient populations and should not be used for patients with known renal cell carcinoma syndromes. Always consider clinical context and additional factors when using this tool. Consult the latest literature and guidelines for comprehensive management strategies.

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