A 52 years old man presents with some difficulty driving at night and reports not seeing cars coming from the sides. He also describes progressive loss of libido and inability to obtain and maintain an erection, which started about 2 years ago. He has gained about 5 kg (11 lbs) in weight over the 2 to 3 years and reports increased fatigue that makes him unable to do the same jobs that he used to do a year ago. On physical examination, the patient has a BMI 35 and abnormal visual fields with bitemporal hemianopia. What is the most likely diagnosis?