Bad gut feeling: a case of recurrent abdominal pain in a young man

A Southeast Asian man in his early 20s with no medical history presented with persistent abdominal pain and nausea for 3 weeks. He reported no recent sick contacts and no travel in the past 5 years since arrival to the USA. Physical examination was notable for right lower quadrant tenderness. CT of the abdomen and pelvis showed hyperaemia and fat stranding near the terminal ileum and cecum, concerning for appendicitis. He underwent laparoscopic appendectomy with pathology showing acute granulomatous appendicitis. Bacterial, fungal and acidfast bacilli (AFB) stains were negative. Given the presence of granulomas, interferon gamma release assay and ACE levels were obtained which were unremarkable. HIV1/2 testing was negative. He unfortunately developed recurrent abdominal pain 4 weeks postoperatively. CT imaging at that time showed pelvic fluid collections, treated empirically with amoxicillin–clavulanic acid for presumed abscesses. The collections persisted despite additional antibiotic rounds, and he eventually presented to the hospital a few months later with worsening abdominal pain and weight loss. CT revealed enlarging fluid collections, and peritoneal wall thickening with intestinal wall oedema (figure 1). Abdominal fluid analysis showed predominance of lymphocytes, with negative bacterial and fungal cultures. Subsequently, upper endoscopy was pursued revealing mild gastritis. Colonoscopy revealed extensive pseudopolyps in the proximal ascending colon with moderate stenosis unable to be transversed (figure 2). QUESTION What is the most likely diagnosis?