A 24-year-old male presented with a 4-year history of abdominal pain, periodic diarrhea, low-grade fever, and easy fatigability is found to have an entero-enteric fistula on contrast radiography. Colonoscopy shows "cobblestone" mucosa that has linear ulcerations with "skip areas" of normal bowel wall. Which of the following is most likely explanation of fistula formation in this patient?