A 58-year-old man with uncontrolled hypertension presents to the emergency department with sudden-onset severe retro-orbital headache, bilateral ptosis, and inability to adduct the right eye. On examination, he has bitemporal hemianopia and altered mental status. MRI of the brain shows a sellar mass with intrinsic T1 hyperintensity and compression of the optic chiasm, as marked **A** in the diagram. Which of the following is the most appropriate IMMEDIATE management step?