<prompt> Please answer with one of the option in the bracket. Write reasoning in between . Write answer in between .Q:A 65-year-old obese man presents to his primary care clinic feeling weak. He was in the military and stationed in Vietnam in his youth. His current weakness gradually worsened to the point that he had to call his son to help him stand to get on the ambulance. He smokes a pack of cigarettes every day and drinks a bottle of vodka a week. He has been admitted for alcohol withdrawal multiple times and has been occasionally taking thiamine, folic acid, and naltrexone. He denies taking steroids. His temperature is 98F 36.7C, blood pressure is 17090 mmHg, pulse is 75min, and respirations are 20min. He is obese with a significant pannus. Hepatomegaly is not appreciable. Abdominal striae are present. His workup is notable for the following:Serum:Na: 142 mEqLCl-: 102 mEqLK: 3.9 mEqLHCO3-: 25 mEqLBUN: 24 mgdLGlucose: 292 mgdLCreatinine: 1.5 mgdLCa2: 10.1 mgdLAST: 7 ULALT: 14 UL24-hour urinary cortisol: 400 μg reference range 300 μgSerum cortisol: 45 pgmL reference range 15 pgmLA 48-hour high dose dexamethasone suppression trial shows that his serum cortisol levels partially decrease to 25 pgmL and his adrenocorticotropin-releasing hormone ACTH level decreases from 10 to 6 pgmL reference range 5 pgmL. What is the best next step in management?? A: CT of the chest, B: MRI of the adrenal glands, C: MRI of the pituitary gland, D: Low-dose dexamethasone therapy for 3 months, E: High-dose dexamethasone therapy for 3 months,  <response>: This is a question about Cushings syndrome in a 65-year-old man with a history of alcohol abuse. The key findings are obesity, abdominal striae, elevated 24-hour urinary cortisol, elevated serum cortisol not fully suppressed by high dose dexamethasone, and partially suppressed ACTH. This indicates ACTH-dependent Cushings syndrome. The partial suppression of ACTH and cortisol with high dose dexamethasone suggests Cushings disease due to a pituitary adenoma. MRI of the pituitary gland would be the best next step to look for a pituitary adenoma causing Cushings disease. CT chest and MRI adrenals would not be helpful since this is ACTH-dependent Cushings. Dexamethasone therapy may help treat the hypercortisolism but does not address the underlying cause.C: MRI of the pituitary gland 