Caught in a Cocoon: Operative Release of Primary Sclerosing Encapsulating Peritonitis With Endoscopic Management of Early Postoperative Duodenojejunal Intussusception.

Sclerosing encapsulating peritonitis (SEP) is a rare cause of small bowel obstruction in which a fibrocollagenous membrane encases the small bowel. Preoperative diagnosis is often difficult because computed tomography (CT) findings may be subtle or atypical. This report highlights a focal proximal jejunal phenotype misinterpreted as an internal hernia on CT and demonstrates a multidisciplinary approach that achieved complete resolution. A 36-year-old man presented with 7-8 weeks of progressive upper abdominal pain, daily bilious vomiting, constipation, and weight loss, with a history of similar self-limiting episodes. CT demonstrated marked gastric and proximal duodenal distension with a distal duodenal transition point and an apparent proximal jejunal abnormality, initially interpreted as a possible internal hernia. Laparotomy identified a dense encapsulating membrane involving the small bowel from the duodenojejunal (DJ) flexure to the mid-jejunum; membrane division and adhesiolysis were performed without bowel resection. Histopathology of the excised membrane demonstrated hyalinized fibrous tissue with mild inflammatory change, without granulomas or malignancy, supporting a diagnosis of idiopathic non-granulomatous encapsulating peritonitis. Postoperatively, persistent proximal obstruction was associated with a short segment of residual DJ intussusception, which was managed successfully with endoscopic pneumatic decompression. At the 28-week email follow-up, the patient reported occasional mild postprandial abdominal discomfort but no frank vomiting, recurrent obstruction, or significant functional impairment. This case illustrates an important diagnostic pitfall: a proximal DJ transition point labeled as an internal hernia (or proximal jejunal cyst) may instead represent focal SEP, particularly in patients with recurrent episodes and no history of prior abdominal surgery. It also reinforces operative principles of complete membrane release and adhesiolysis with bowel preservation whenever possible. Persistent postoperative obstruction despite surgical release may reflect discrete mechanical complications. In clinically stable patients, CT findings can guide decision-making and may permit non-operative or endoscopic management. SEP may present with a proximal jejunal phenotype that mimics an internal hernia on CT and is often confirmed only intraoperatively. Early postoperative obstruction may require individualized multidisciplinary escalation based on clinical status and imaging findings.