A 42-year-old man with a 2-year history of resistant hypertension presents with episodic headaches, palpitations, and profuse diaphoresis. Plasma fractionated metanephrines are elevated. CT abdomen shows the structure marked **A** — a heterogeneous adrenal mass measuring 4.5 cm with non-contrast Hounsfield units of 18, avid heterogeneous enhancement, and delayed washout <50%. Which of the following best describes the cellular origin and pathophysiology of this lesion?
A. Steroid-secreting tumor arising from the zona fasciculata of the adrenal cortex
B. Lipid-rich adenoma arising from the zona reticularis with minimal hormone production
C. Catecholamine-secreting tumor arising from chromaffin cells of the adrenal medulla
D. Metastatic neuroendocrine carcinoma arising from the organ of Zuckerkandl
Explanation
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The structure marked A — a heterogeneous adrenal mass with avid enhancement, elevated metanephrines, and the classic triad of headaches, palpitations, and diaphoresis — is pathognomonic for pheochromocytoma. Pheochromocytoma is a catecholamine-secreting tumor arising from chromaffin cells of the adrenal medulla in 90% of cases. The CT findings (non-contrast HU >10, heterogeneous enhancement, delayed washout <50%) are characteristic and distinguish it from lipid-rich adenomas. The biochemical confirmation via elevated plasma fractionated metanephrines is the gold standard diagnostic test (sensitivity ~99%), and the clinical presentation (resistant hypertension with episodic symptoms) is the classic triad with 90% sensitivity and 95% specificity when all three features are present. (Endocrine Society Pheochromocytoma Guidelines 2014)
Why each distractor is wrong
Option 2 (zona fasciculata steroid-secreting tumor): While adrenocortical adenomas do arise from the adrenal cortex, they do not produce catecholamines or cause the classic triad of headaches, palpitations, and diaphoresis. Elevated metanephrines would not occur with cortical tumors. This represents confusion between adrenal cortical and medullary pathology.
Option 3 (lipid-rich adenoma): Lipid-rich adenomas are benign cortical lesions with non-contrast Hounsfield units <10 (this patient's HU is 18, >10). They do not secrete catecholamines and would not produce elevated metanephrines or the clinical triad. This is a common distractor testing understanding of CT density criteria.
Option 4 (metastatic paraganglioma from organ of Zuckerkandl): While extra-adrenal paragangliomas do arise from the organ of Zuckerkandl (and account for 10% of pheochromocytomas per the 10% rule), the imaging clearly shows an adrenal mass, not an extra-adrenal location. This distractor tests knowledge of the 10% rule but misapplies it to the anatomic location shown.
High-YieldNEET PG
Pheochromocytoma = chromaffin cell tumor of adrenal medulla (90%); diagnosis is biochemical first (plasma fractionated metanephrines, sensitivity ~99%), then localize with imaging (CT: HU >10, heterogeneous enhancement, delayed washout <50%).
Endocrine Society Pheochromocytoma Guidelines 2014
