Acute Diverticulitis Hinchey Grading

A 62-year-old man with chronic constipation and low-fiber diet presents with 4 days of worsening left lower quadrant pain, low-grade fever (38.4°C), and altered bowel habit. He is hemodynamically stable with focal left iliac fossa tenderness but no generalized peritonitis. Labs show WBC 15.2 with neutrophilia, CRP 148 mg/L, normal lactate, and negative urinalysis. Contrast-enhanced CT abdomen and pelvis is performed. The structure marked **C** in the diagram represents a confined pericolic abscess (Hinchey Ib collection). Which of the following is the most appropriate next step in management of this patient?