A 42-year-old woman from Mumbai is referred after incidental discovery of a 2.5 cm right adrenal mass on CT abdomen done for abdominal pain. She has a history of medullary thyroid carcinoma (MTC) diagnosed 3 years ago, treated with total thyroidectomy. Serum calcitonin is 180 pg/mL (normal <10). Plasma metanephrines are elevated: normetanephrine 1.8 nmol/L (normal <0.9). Genetic testing shows a RET M918T mutation. What is the next step in management?