Adrenal Adenoma

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?