This is a complete (absolute constipation) large bowel obstruction from a rectosigmoid tumour with a markedly distended caecum (11 cm), so it needs urgent operative relief. The lecture notes say acute mechanical obstruction is treated by rapid resuscitation followed by urgent relief, usually by operation. NGT suction and observation for 48 h is the approach for adhesive SBO, not a closed obstructing colonic tumour, and a barium enema adds delay and risk.