Please refer to the attached table to answer the following question: A 55-year-old female presents for evaluation in your clinic for new-onset type 2 diabetes. Her exam is notable for supraclavicular fat pad filling, central adiposity, muscle weakness, and thinning of the skin. Her 24 hour urine free cortisol levels were markedly elevated, as was ACTH. Results of peak ACTH levels from cavernous sinus sampling are shown in the attached table. The most likely cause of her signs and symptoms is which of the following?
Select one of the following: