A 37-year-old is hospitalized for 2 weeks with epigastric pain radiating to his back, nausea, and vomiting. Initial laboratory values revealed an elevated amylase level consistent with acute pancreatitis. He complains of early satiety, epigastric pain, and fevers. His white blood cell (WBC) count is 23,000/mm" and his amylase level is normal. CT scan demonstrating a 6 cm by 6 cm rim-enhancing fluid collection in the body of the pancreas. Which is most definitive management of the fluid collection?