A patient with newly diagnosed non-small cell lung cancer (NSCLC) undergoes FDG-PET/CT for staging. PET shows increased uptake in a right hilar node and an adrenal lesion. If the adrenal lesion has a CT attenuation of 5 HU on non-contrast CT and low FDG uptake (SUV 1.8), what is the most likely interpretation of the adrenal finding?
- A Adrenal metastasis — upstage to M1b
- B Benign adrenal adenoma — intracytoplasmic lipid causing low attenuation; FDG non-avid ✓
- C Adrenal phaeochromocytoma — incidental finding
- D Adrenal carcinoma — low-grade non-avid lesion
Correct answer: B. Benign adrenal adenoma — intracytoplasmic lipid causing low attenuation; FDG non-avid
Explanation
An adrenal lesion with CT attenuation ≤10 HU on unenhanced CT is characteristic of a lipid-rich adrenal adenoma (intracytoplasmic lipid causes negative or low Hounsfield units). Combined with low FDG uptake (SUV 1.8 — below the threshold for metabolic activity), this is a benign adenoma. Adrenal metastases are typically FDG-avid (SUV >3.0) and have higher CT attenuation (>20 HU) or show significant washout pattern on adrenal protocol CT. Misclassification of adrenal adenomas as metastases would incorrectly upstage the patient to Stage IV.
Reference: Grainger & Allison's Diagnostic Radiology, 7th ed.
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