A 54-year-old woman undergoes contrast-enhanced CT abdomen for evaluation of right flank pain. Imaging reveals an incidental left adrenal mass. She is asymptomatic with no clinical features of Cushing syndrome, pheochromocytoma, or primary aldosteronism. Biochemical screening (plasma metanephrines, aldosterone-to-renin ratio, and 1 mg overnight dexamethasone suppression test) is normal, confirming a nonfunctioning incidentaloma. Non-contrast CT is performed for imaging characterization. The structure marked **A** in the diagram demonstrates homogeneous attenuation of 6 Hounsfield units with smooth, well-defined margins and measures 2.5 cm. Based on this imaging finding, what is the most likely diagnosis and appropriate management?
A. Pheochromocytoma; urgent alpha-blockade followed by beta-blockade and surgical resection
B. Benign lipid-rich cortical adenoma; no surgical resection required, reassurance and discharge without routine follow-up imaging
C. Metastatic malignancy to adrenal; staging imaging and chemotherapy based on primary tumor type
D. Adrenocortical carcinoma; urgent surgical resection and adjuvant mitotane therapy indicated
Explanation
Why "Benign lipid-rich cortical adenoma; no surgical resection required, reassurance and discharge without routine follow-up imaging" is right
The structure marked A — a homogeneous left adrenal mass with attenuation of 6 Hounsfield units (HU) — is the hallmark imaging finding of a benign, lipid-rich cortical adenoma. According to the Fassnacht et al. (ESE 2016) guideline, an attenuation <10 HU on non-contrast CT is approximately 70% sensitive and 98% specific for a benign adenoma. Combined with normal biochemical screening (excluding hormone hypersecretion), smooth margins, small size (<4 cm), and absence of invasion, this lesion meets all criteria for a clearly benign nonfunctioning adenoma. Recent ESE guidelines no longer recommend routine follow-up imaging for such lesions; the patient can be reassured and discharged.
Why each distractor is wrong
Adrenocortical carcinoma; urgent surgical resection and adjuvant mitotane therapy indicated: Adrenocortical carcinoma typically presents with high attenuation (>20 HU), irregular margins, heterogeneity, invasion of adjacent structures, and/or biochemical evidence of hormone excess. The marked A lesion has attenuation well below 10 HU, which is 98% specific for benignity and excludes malignancy.
Pheochromocytoma; urgent alpha-blockade followed by beta-blockade and surgical resection: Pheochromocytoma is excluded by normal plasma and 24-hour urinary metanephrines. Although pheochromocytomas can have variable attenuation, the biochemical screening is the decisive exclusionary test here.
Metastatic malignancy to adrenal; staging imaging and chemotherapy based on primary tumor type: Metastatic lesions typically show heterogeneous enhancement, higher attenuation, and irregular margins. The low attenuation (<10 HU) and homogeneous appearance of structure A are incompatible with metastatic disease.
High-YieldNEET PG
Attenuation <10 HU on unenhanced CT is the single best imaging criterion for benign adrenal adenoma (98% specific); combined with normal biochemistry and size <4 cm, it permits safe discharge without follow-up imaging per ESE 2016 guidelines.
Fassnacht M et al. Management of adrenal incidentalomas: European Society of Endocrinology Clinical Practice Guideline. Eur J Endocrinol 2016;175(2):G1-G34.
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