A 32-year-old woman presents to the clinic with a 6-month history of progressive hypertension (BP 165/105 mmHg), episodic severe headaches, and profuse sweating. Her 24-hour urinary metanephrines are markedly elevated at 2.8 times the upper limit of normal. Imaging reveals a 3 cm right adrenal mass. On further evaluation, she is found to have a serum calcitonin of 285 pg/mL (normal <10) with a normal serum calcium. Thyroid ultrasound shows a hypoechoic nodule. Her 28-year-old brother was recently diagnosed with medullary thyroid cancer. Genetic testing reveals a RET proto-oncogene mutation (codon 634). Which of the following is the most appropriate next step in management?