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Index / Incidental findings

Adrenal incidentaloma & washout

ACR 2017CTMRI
Flowchart · click to enlarge
Incidental adrenal lesion

Unenhanced attenuation ≤10 HU is diagnostic of lipid-rich adenoma. For indeterminate lesions, adrenal-protocol CT with 15-minute delayed phase calculates washout.

Management

Diagnostic thresholds

FindingInterpretation
Unenhanced ≤10 HULipid-rich adenoma No follow-up
Absolute washout ≥60%Adenoma
Relative washout ≥40% (no unenhanced phase)Adenoma
Stable ≥1 yearBenign
Macroscopic fatMyelolipoma
≥4 cm without benign features, no cancer historyConsider resection

APW = (Enhanced − Delayed) ÷ (Enhanced − Unenhanced) × 100
RPW = (Enhanced − Delayed) ÷ Enhanced × 100

Figure · click to enlarge
Absolute and relative washout formulas
Washout
APW–RPW–
Some pheochromocytomas, hypervascular metastases (RCC, HCC) and carcinomas can wash out. Interpret in clinical context; check biochemistry for functioning lesions.

Sources

  1. Mayo-Smith WW, Song JH, Boland GL, et al. Management of incidental adrenal masses: a white paper of the ACR Incidental Findings Committee. J Am Coll Radiol. 2017;14:1038–1044.PubMed ↗
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Radessential summarizes published classification systems for practicing radiologists. Summaries are condensed; confirm details against the cited source before relying on them for patient care.