Emergency department with abdominal pain and distention

A 64-year-old man presents to the emergency department with abdominal pain and distention, as well as constipation of 8 days’ duration. He denies vomiting, fever, diarrhea, or dysuria. Except for hypertension, he is otherwise healthy with no prior surgeries. His vital signs are normal except for a borderline pulse of 99 bpm. His physical examination is unremarkable except for his abdomen, which is large, rotund, and tympanitic. There is diffuse tenderness everywhere in the abdomen. 1. What history would you want to obtain? 2. What differential diagnoses would you consider? 3. List and describe the specific diagnostic tests you might order to determine cause of his concern?