Double Trouble: A Diagnostic Challenge of Coexisting Encapsulating Peritonitis and Transverse Mesocolic Internal Hernia Presenting As Acute Small Bowel Obstruction.

Encapsulating peritonitis (EP), also known as abdominal cocoon syndrome, and internal hernia are uncommon yet important causes of small bowel obstruction (SBO). Their true coexistence is exceedingly rare and presents a unique diagnostic challenge. Despite their distinct pathogenesis, both entities can rarely share considerable clinical and radiological overlap. We report the case of a 29-year-old man who presented with acute abdominal pain and multiple episodes of non-projectile, non-bilious, non-blood-stained vomiting. Contrast-enhanced computed tomography demonstrated clustered dilated small bowel loops enclosed within an enhancing fibro-collagenous membrane, consistent with EP. In addition, mesenteric vascular convergence and a focal transition point within the transverse mesocolon raised suspicion for a concomitant internal hernia. Emergency exploratory laparotomy confirmed a dense fibro-collagenous membrane encasing the small bowel, together with a transmesocolic internal hernia through a defect in the transverse mesocolon. Complete excision of the encapsulating membrane, meticulous adhesiolysis, reduction of the herniated bowel, and closure of the mesocolic defect resulted in complete resolution of the obstruction and an uneventful postoperative recovery. This case highlights the exceptionally rare coexistence of EP and a transmesocolic internal hernia, two entities that have traditionally been described as radiological mimics rather than concurrent pathologies. Previous case reports have primarily described EP and internal hernia as independent causes of SBO, rarely also highlighting one entity as a radiological mimic of the other; however, their concurrent occurrence in the same patient is extremely rare. This case highlights the importance of a systematic computed tomography evaluation, as recognition of one diagnosis should not preclude careful assessment for the other, with direct implications for surgical planning and optimal patient management.