Incidental adrenal nodules are common on abdominal CT, and most are benign adenomas. A single unenhanced attenuation measurement settles the majority without further imaging.
Measure attenuation through the nodule on unenhanced CT: a homogeneous nodule of 10 Hounsfield units or less is a lipid-rich adenoma and needs no further workup. Above 10 Hounsfield units, the nodule is indeterminate on unenhanced imaging and warrants a dedicated adrenal protocol with washout, or follow-up, depending on size and history.
Two cautions keep this safe: use it for a well-defined, homogeneous nodule, not a heterogeneous or large mass, and raise the threshold for concern in a patient with a known primary malignancy or biochemical hyperfunction, where tissue characterisation or endocrine evaluation takes priority over the attenuation rule alone.
- Measure unenhanced attenuation through an incidental adrenal nodule.
- A homogeneous nodule of 10 Hounsfield units or less is a benign lipid-rich adenoma needing no further imaging.
- Above 10 Hounsfield units, use a dedicated adrenal washout protocol or follow-up.
- Apply the rule to well-defined homogeneous nodules, and be more cautious with a known malignancy or hormone excess.
Why it matters
A single attenuation value resolves most adrenal incidentalomas, sparing patients unnecessary follow-up scans.
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