Review Question - QID 214836

A 52-year-old man presents to the emergency department for visual impairment affecting both eyes. Over the last 2 weeks, he has been bumping into objects in his home. He denies any ocular pain and trauma or using eye drops. He does not endorse a headache or any focal motor or sensory deficits. The patient reports having generalized fatigue that has progressively worsened over the last 1-2 months, and his family members have found it strange that he wears a sweater in the summer. He otherwise has no significant past medical history and takes no medications. His temperature is 98.6°F (37.0°C), blood pressure is 130/90 mmHg, pulse is 65/min, and respirations are 12/min. Neurological examination is notable for bilateral superior temporal quadrantanopsia noted on visual field testing. Laboratory studies are shown below:

Na+: 140 mEq/L
Cl-: 98 mEq/L
K+: 3.7 mEq/L
HCO3-: 22 mEq/L
BUN: 10 mg/dL
Glucose: 105 mg/dL
Creatinine: 0.8 mg/dL
Thyroid-stimulating hormone: 0.2 µU/mL
Free T4: 0.3 ng/dL
Prolactin: 15 ng/mL
Alpha-subunit: Markedly increased

An MRI of the brain with and without contrast is shown in Figure A. Which of the following is the most appropriate next step in management?