A 38-year-old woman from rural Maharashtra presents with episodic severe headaches, profuse sweating, and palpitations for 3 months. Her blood pressure during an episode is 180/110 mmHg, dropping to 130/80 mmHg between episodes. She denies chest pain or dyspnea. Physical examination reveals no neurofibromatosis stigmata. Plasma free metanephrines are elevated at 4.2 nmol/L (normal <0.9). CT abdomen shows a 3.5 cm left adrenal mass with heterogeneous enhancement. 24-hour urine metanephrines are also elevated. What is the most appropriate next step in management?