A 4-month-old child was admitted to a surgical department 8 hours after the first attack of anxiety. The attacks happen every 10 minutes and last for 2-3 minutes, vomiting occurred once. Objectively: the child's condition is grave. Abdomen is soft, palpation reveals a tumor-like formation in the right iliac area. After rectal examination the doctor's finger was stained with blood. What is the most probable diagnosis?