A 54-year-old man presents to the clinic with progressive ri…
A 54-year-old man presents to the clinic with progressive right-sided flank pain and difficulty urinating for the past two days. He reports intermittent nausea but no fever. Physical exam reveals tenderness in the right flank and a palpable abdominal mass. Laboratory studies show an elevated serum creatinine and mild electrolyte abnormalities. Urinalysis is unremarkable. What is the initial imaging study of choice to evaluate this condition?