RENAL LESIONS
Last modified: October 6, 2025
Main references: ACR 2018, CAR 2019
1 - Incidental renal lesions on ultrasound
Title 4
2 - Incidental renal lesions on CT C-
3 - Incidental renal lesions on CT C+
4 - Cystic lesions (Bosniak)
5 - Solid kidney lesions
6 - Solid renal lesions with fatty components
Target population
≥18 years old
CT performed for context other than evaluation of the urinary system
Exclusions
History of primary neoplasia
Genetic syndrome predisposing to neo-renal disease
Important Notes
Significant growth
Average increase of ≥ 4 mm/year
Stability
Average growth of ≤ 3 mm/year in 5 years = benign
Lesion measurement in the above algorithms refers to the largest diameter among all planes
Additional Notes
40% of patients have cysts on CT scan
Probability of neoplasia according to Bosniak classification⁴
Bosniak I = 3.2%
Boaniak IIi = 6%
Bosniak IIF = 6.7%
Bosniak III = 55.1%
Bosniak IV = 91%
MRI preferred, especially for lesions too small to be characterized (<15 mm)
CT also acceptable depending on availability
Angiomyolipoma < 4 cm
Support is controversial
Some prefer to follow up to ensure there is no rapid growth
For patients at high surgical risk or limited life expectancy, surveillance or no further investigation may be adequate rather than invasive treatment.
Stage T1 neoplastic lesions (mass or Bosniak IV), no significant progression after 41 months
Management to be reassessed if patient becomes symptomatic
Definitions
•Rehaussement
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CT – densité entre C- et C+
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≤ 10 HU Absence de rehaussement
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>10 à < 20HU Rehaussement équivoque pour lésion corticale
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>15 à < 20HU. Rehaussement équivoque pour lésion large ou exophytique
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≥ 20HU Rehaussement franc
-
-
MRI
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Augmentation de 15% de l’intensité du signal à 2-4 minutes post injection
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Signal intense sur phases de soustraction
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Changement de morphologie
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Changement dans l’hétérogénéité : changement de contour, densité ou nombre de septa
Septum
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Image linéaire ou curvilnéaire connectant deux surfaces
Nombre de septa
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Quelques: 1-3
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Multiples: ≥ 4
Épaisseur de septum ou paroi
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Si protrusion de part et d'autre de la paroi ou septum, épaisseur totale perpendiculaire à la paroi à considérer en excluant l'épaisseur de la paroi ou du septum sous-jacent
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Mince : ≤ 2 mm
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Minimalement épaissi: 3 mm (Bosniak IIF)
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Épais: ≥ 4 mm
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Irrégulier : protrusion de ≤ 3 mm présentant des marges obtuses (Bosniak III)
Nodule
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Protrusion avec marges algues
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Protrusion de ≥ 4 mm avec marges obtuses
Figures
Figure 1. Original CAR 2019 recommendations for renal lesions on C-CT scans
Figure 2. Original CAR 2019 recommendations for renal lesions on C+ CT scans
Figure 3. Original CAR 2019 recommendations for renal lesions on ultrasound
Figure 4. Original CAR 2019 recommendations for cystic renal lesions
Figure 5. Original CAR 2019 recommendations for renal masses
Figure 6. Original CAR 2019 recommendations for renal masses with fatty components
Table 1. Original table of the Bosniak 2019 classification
References
Kirkpatrick IDC, Brahm GL, Mnatzakanian GN, Hurrell C, Herts BR, Bird JR. Recommendations for the Management of the Incidental Renal Mass in Adults: Endorsement and Adaptation of the 2017 ACR Incidental Findings Committee White Paper by the Canadian Association of Radiologists Incidental Findings Working Group. Canadian Association of Radiologists Journal. 2019;70(2):125-133. doi:10.1016/j.carj.2019.03.002
Herts BR, Silverman SG, Hindman NM, Uzzo RG, Hartman RP, Israel GM, Baumgarten DA, Berland LL, Pandharipande PV. Management of the Incidental Renal Mass on CT: A White Paper of the ACR Incidental Findings Committee. J Am Coll Radiol. 2018 Feb;15(2):264-273. doi: 10.1016/j.jacr.2017.04.028
Silverman, Stuart G., et al. “Bosniak Classification of Cystic Renal Masses, Version 2019: An Update Proposal and Needs Assessment.” Radiology, vol. 292, no. 2, Aug. 2019, p. 475–488, doi:10.1148/radiol.2019182646
Sevcenco, Sabina, et al. “Malignancy Rates and Diagnostic Performance of the Bosniak Classification for the Diagnosis of Cystic Renal Lesions in Computed Tomography – a Systematic Review and Meta-Analysis.” European Radiology, vol. 27, no. 6, 19 Oct. 2016, pp. 2239–2247, www.ncbi.nlm.nih.gov/pmc/articles/PMC5408031/pdf/330_2016_Article_4631.pdf, doi:10.1007/s00330-016-4631-9 .