A 44-year-old woman is evaluated for weight gain, muscle weakness, and metabolic syndrome. She has hirsutism but also notes hair loss on her head. She has been amenorrheic for 2 years.
Medical history is significant for hyperlipidemia, type 2 diabetes mellitus, hypertension, and obesity. Medications are atorvastatin, metformin, and lisinopril.
On physical examination, blood pressure is 156/92 mm Hg and pulse rate is 78/min. BMI is 42. She has a cushingoid appearance, acne, and moderate hirsutism affecting the chin, upper lip, breasts, back, and chest. There are several wide violaceous striae across the abdomen and the back of her arms.
Adrenocorticotropic hormone (ACTH) | 52 pg/mL (11.4 pmol/L) |
Cortisol 8 AM after 1 mg of dexamethasone the night before | 5.2 µg/dL (143.5 nmol/L) |
24-Hour urine cortisol excretion | |
Initial measurement | 124 µg/24 h (341.7 nmol/24 h) |
Repeat measurement | 98 µg/24 h (270.0 nmol/24 h) |
Intrapetrosal sinus sampling identifies a pituitary microadenoma as the source of the high ACTH level.
Which of the following is the most appropriate test to perform next?