Primary aldosteronism caused by unilateral adrenal hyperplasia: rethinking the accuracy of imaging studies

A rare type of aldosteronism, known as unilateral adrenal hyperplasia (UAH), is difficult to diagnose, not only because it fails to conform to the typical common subtypes, but also because imaging results are unreliable. We report 2 Taiwanese patients with UAH. Case 1 was a 44-year-old man with 2 episodes of hypokalemic paralysis. Hypertension and suppressed plasma renin activity (PRA) with elevated plasma aldosterone concentration (PAC) were observed. Abdominal computed tomography (CT) and magnetic resonance imaging (MRI) showed a right adrenal mass, but adrenal scintigraphy revealed no definite laterality. The patient underwent a laparoscopic right adrenalectomy. Adrenal cortical hyperplasia was discovered from results of the histologic analysis. Case 2 was a 33-year-old woman referred for hypokalemia, hypertension, and a left adrenal mass found on a CT scan. However, MRI revealed normal adrenal glands. The adrenal vein sampling for PAC showed overproduction of PAC from the left adrenal gland. A laparoscopic left adrenalectomy was done. Pathology results revealed micronodular cortical hyperplasia with central hemorrhage. Blood pressure, plasma potassium, aldosterone, and renin activity levels returned to normal after operation in both cases. Both patients have been well for 3 years and 16 months, respectively, after surgery. We review the literature and discuss the limitations of imaging studies.