A 35-year-old man with a 5-year history of Crohn's disease presents with acute onset of severe abdominal pain, fever (38.5°C), and abdominal distension. He has not had a bowel movement in 3 days. On examination, he has marked tenderness in the right lower quadrant with guarding and rebound tenderness. Plain abdominal X-ray shows dilated small bowel loops with air-fluid levels. CT abdomen with contrast reveals a thick-walled segment of terminal ileum with surrounding fat stranding and a 4 cm × 3 cm collection in the right iliac fossa. What is the most appropriate immediate management?