Incidental Renal Mass (CT)
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ACR IFC 2018·reviewed 2026-07-01
- •Applies to incidentally detected renal masses in patients ≥18 years. Suspicious features at any size (enhancing soft tissue, thick/enhancing septa or wall, or a mural nodule) warrant urologic referral rather than routine follow-up.
- •'Enhancement' means an unequivocal attenuation increase ≥20 HU on a properly timed multiphase CT (or MRI); increases of 10–20 HU are indeterminate ('pseudoenhancement') and often need MRI or dedicated renal-mass CT.
- •A homogeneous mass measuring −10 to +20 HU on a well-performed single-phase study behaves as a benign (Bosniak I/II) cyst even without a dedicated protocol; homogeneous masses ≥70 HU on unenhanced CT are benign hyperdense cysts.
- •Cystic masses with any complexity should be categorized with Bosniak v2019 (see linked criteria) rather than this size-only pathway.
- •In patients with a known primary malignancy or hematuria, lower the threshold for dedicated characterization and urologic input.
Can the mass be characterized on this study?
A mass is 'too small to characterize' (TSTC) when it is too small to reliably assess attenuation/enhancement — typically <1 cm on a routine single-phase CT.
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Sources
- Herts BR, et al. Management of the Incidental Renal Mass on CT: A White Paper of the ACR Incidental Findings Committee. J Am Coll Radiol. 2018;15(2):264-273.
- Silverman SG, et al. Bosniak Classification of Cystic Renal Masses, Version 2019: An Update Proposal and Needs Assessment. Radiology. 2019;292(2):475-488.source
Educational reference for clinicians — not medical advice. Verify against the primary source before acting on it; guidelines change. Final decisions rest with the interpreting physician and your institution's protocols.