A 40-year-old woman has experienced increasingly frequent episodes of weakness accompanied by numbness and tingling in her hands and feet for the past year. On examination, her blood pressure is 168/112 mm Hg. Laboratory studies show sodium, 142 mmol/L; potassium, 2.9 mmol/L; chloride, 104 mmol/L; HCO3-, 28 mmol/L; and glucose, 74 mg/dL. Her plasma renin activity is low. Which of the following radiologic findings is most likely to be present in this woman?

Hypokalemia with neuromuscular irritability, hypertension, and low plasma renin suggests hyperaldosteronism. The most common cause for primary hyperaldosteronism is idiopathic adrenal cortical nodular hyperplasia. An insulinoma arising in the pancreas could account for episodic weakness, but the glucose level would be low. About 10% of pheochromocytomas are extra-adrenal, including para-aortic, and could account for hypertension from catecholamine excess, but there would not be hypokalemia. Thyroid enlargement could be Graves' disease, though it is usually diffuse, and could account for weakness and hypertension, but with wider pulse pressure, and without hypokalemia. A malignancy in the chest is more likely to be the cause of a paraneoplastic syndrome, but that is unlikely to be hypokalemia.