Background: Peritoneal encapsulation (PE) syndrome is a rare congenital condition with an accessory peritoneal sac covering the small bowel. PE is mostly reported to be asymptomatic and detected incidentally, however, it can present as a rare cause of gut obstruction if there is peritoneal inflammation as our case report.
Case Report: A Thai 47-year-old man presented with clinical of small bowel obstruction in virgin abdomen. Physical examination revealed abdominal distension with large palpable cystic lesion in abdomen. CT scan revealed small bowel loops within a thin membranous sac in the mid-abdomen containing fluid and a disproportion point at duodenojejunal junction. Exploratory laparotomy was performed, and found a peritoneal cyst in the mid-abdomen containing entire small bowel and clear yellow fluid. Stomach and the large bowel were located outside of the cyst. There was a band of the peritoneal membrane causing obstruction at the duodenojejunal junction. The cyst was opened, and its membrane and fluid were sent for pathological,
cytological and microbiological examination. Obstruction point was released. Post-operative course was uneventful. The pathological report revealed chronic granulomatous inflammation; tissue polymerase chain reaction for tuberculosis was found positive. The patient was treated with anti-tuberculosis drugs and had no further symptom of gut obstruction.
Conclusion: Peritoneal tuberculosis is likely to be an aggravating factor for gut obstruction in peritoneal encapsulation syndrome, which is a congenital condition, by causing the peritoneal thickening and obstruction at duodenojejunal junction.

Keywords: Peritoneal encapsulation, Sclerosing encapsulating peritonitis, Cocoon abdomen, Peritoneal tuberculosis, Intestinal
obstruction