Utility of F-18 FDG-PET in Detecting Primary Aldosteronism in Patients with Bilateral Adrenal Incidentalomas
A 53-yr-old man was referred to our clinic on September 5, 2011 after bilateral adrenal masses (right: 1 cm, left: 2.5 cm) were discovered on an abdominal CT (). Two years prior, the patient underwent low anterior resection for sigmoid colon cancer and had received adjuvant chemotherapy. The patient had been prescribed antihypertensive medications (almodipine 10 mg, olmesartan 20 mg) for 12 yr, but his blood pressure could not be controlled well and was found to be 160/90 mmHg on presentation. He was generally well-appearing, but complained of a persistent mild headache. He demonstrated an increased deep tendon reflex in both knees and had no weight gain or edema. Blood analysis revealed persistent hypokalemia (serum potassium of 2.6 mM), but his medications did not include a potassium-wasting diuretic (e.g., thiazide, loop). Laboratory tests showed plasma renin activity (PRA) of 0.12 ng/mL/h and plasma aldosterone concentration (PAC) of 10.4 ng/dL with a PAC/PRA ratio of 86.6. And we confirmed diagnosis of primary aldosteronism with captopril challenge test (post-captopril aldosterone level was 18.5 ng/dL).\nGiven his history of colon cancer, we had to rule out metastatic disease before continuing to adrenal venous sampling. FDG-PET/CT of his torso incidentally revealed a focal hypermetabolic lesion in the right adrenal gland (). Generally, the larger tumor has more focal hypermetabolic uptake lesion. But in this case, although right adrenal incidentaloma was smaller than left that, only right adrenal gland had focal hypermetabolic uptake. There was no hypermetabolic uptake except adrenal gland in FDG-PET/CT, the patient was suspected primary aldosteronism clinically. So we thought that right adrenal incidentaloma was not metastatic lesion but benign functioning tumor. Adrenal venous sampling was performed at both adrenal glands, and the aldosterone/cortisol ratio was found to be 15 times higher on the right side than on the left (). This finding was consistent with the results of FDG-PET/CT.\nSurgical resection of the right adrenal gland was performed. Pathological examination showed a well-demarcated, golden yellow nodule grossly () with tumor cells that resembled cortical cells and showed lipid-laden clear cells microscopically (). Three months after the operation, the patient's blood pressure, serum potassium level, and plasma renin-aldosterone activity were normalized.