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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? *

MRI

What is the scan's protocol? *

Noncontrast CT

Portal venous phase CT

Renal mass protocol CT

Which one best describes the lesion? *

Homogenous, with attenuation of ≥70 HU

Homogenous, with attenuation of -9 to 20 HU

Homogenous, low attenuating, and too small to characterize

Neither

Which one best describes the lesion? *

Homogenous, with attenuation of 21-30 HU

Homogenous, low attenuating, and too small to characterize

Neither

Does the lesion have imaging features of a solid mass? *

>3cm or ≥25% hyperattenuating tissue

Heterogenous non-enhancing lesion

Abundant calcification

Macroscopic fat

Neither

Does the lesion have any enhancing nodule(s)*? *

Yes

*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? *

1-3 septa that are ≤2 mm thick

≥4 septa that are ≤2 mm thick

≥1 septa that are smooth and 3 mm thick

≥1 septa that are ≥4 mm thick

≥1 septa that are irregular (displaying ≤3 mm obtusely margined convex protrusion)

Lesion does not have any septa

How are the lesion's walls? *

Irregular (displaying ≤3 mm obtusely margined convex protrusion)

≥4 mm thick

Smooth and 3 mm thick

Smooth and thin (≤2 mm) (± enhancement)

How is the lesion's attenuation? *

-9 to 20 HU

>20 HU

Does the lesion have any calcifications? *

Yes

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? *

Unenhanced MRI

Renal mass protocol MRI

Which one best describes the lesion? *

Homogenous, and T2w intensity similar to CSF

Homogenous, and T1w fat sat signal intensity is ≥2.5x the kidney

Neither

Does the lesion have any of the following features? *

≥25% enhancing tissue

Macroscopic fat

Neither

Does the lesion have any enhancing nodule(s)*? *

Yes

*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? *

1-3 septa that are ≤2 mm thick

≥4 septa that are ≤2 mm thick

≥1 septa that are smooth and 3 mm thick

≥1 septa that are ≥4 mm thick

≥1 septa that are irregular (displaying ≤3 mm obtusely margined convex protrusion)

Lesion does not have any septa

How are the lesion's walls? *

Irregular (displaying ≤3 mm obtusely margined convex protrusion)

≥4 mm thick

Smooth and 3 mm thick

Smooth and thin (≤2 mm) (± enhancement)

Is the lesion nonenhancing and heterogenously hyperintense at T1w fat sat imaging? *

Yes

Is the lesion's intensity homogenous and similar to CSF on T2w imaging? *

Yes

Does the lesion have any calcifications? *

Yes

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

Reference:

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
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

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Rad at Hand » Radiology Calculators » Abdominal Imaging’s Calculators » Bosniak 2019 Classification of Renal Cystic Masses (CT/MRI)

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