Diverticulitis Sigmoid Wall Thickening

A 58-year-old male presents to the emergency department with left lower quadrant pain for three days, low-grade fever (38.1°C), and change in bowel habits. Graded-compression ultrasound of the left iliac fossa using a high-frequency linear probe is performed. The structure marked **A** in the diagram shows segmental thickening of the sigmoid colon wall with loss of normal gut-wall layering over 6 cm, in the setting of hypoechoic diverticula, hyperechoic inflamed pericolic fat, and a small adjacent fluid collection. Laboratory investigations reveal leukocytosis (14,000/mm³ with left shift), elevated C-reactive protein (96 mg/L), and mildly elevated procalcitonin. What is the most appropriate next step in management of this patient?