Cystic renal mass classification — pick your modality, then the most aggressive feature present.
Dominant feature
Select a feature
Pick the most aggressive feature the cyst shows.
Applies only to cystic masses — v2019 defines a cystic mass as one in which less than approximately 25% is composed of enhancing tissue. A predominantly solid or necrotic enhancing mass is not Bosniak-classifiable; do not run it through this page (it is managed as a solid renal mass, not as a class IV cyst). Bosniak v2019 (Silverman et al., Radiology 2019). Requires a dedicated renal-mass-protocol CT or MRI. Enhancement = ≥20 HU increase on CT, or a ≥15% signal-intensity increase on MRI. Attenuation (HU) criteria are CT-specific and phase-specific — a ≥70 HU homogeneous mass is class II only at noncontrast CT; the same value on a contrast-enhanced phase may be enhancing solid tumour. Classes I, III and IV use the same definitions on both modalities; classes II and IIF differ — the signal-intensity subtypes replace the HU subtypes, and heterogeneous hyperintensity on unenhanced fat-saturated T1 is an MRI-only class IIF criterion (a papillary RCC mimic, and the one IIF finding that needs no enhancing feature). Decision support only — not a substitute for clinical judgment.
Silverman SG, et al. Bosniak Classification of Cystic Renal Masses, Version 2019. Radiology. 2019;292(2):475–488.