An Unexpected Cause of Abdominal Discomfort: Non-pancreatic Mesenteric Pseudocyst.

Mesenteric cysts (MCs), rare entities of embryologic origin, predominantly affect the small bowel's mesentery. The clinical manifestations of MCs often lack specificity, which complicates diagnosis. Given their rarity, detailed reporting of MC cases is essential to enhance understanding and improve treatment strategies. We present a case of a 45-year-old male who presented to the emergency department with a one-month history of abdominal pain in the umbilical region, postprandial fullness, progressive decrease in food intake, 12 kg weight loss, and increased abdominal girth. Computed tomography (CT) imaging revealed a well-defined mass in the jejunoileal area. During the exploratory laparotomy, we identified and excised a fibrotic mass on the mesentery of the ileal jejunum, which was not adherent to the intestines. We discharged the patient with no complications following an uneventful four-day observational period. Histopathological examination, including immunohistochemical staining, confirmed the lesion as a non-pancreatic mesenteric pseudocyst. On the follow-up visit, the patient reported no complications. This case report underscores the solitary, multilocular nature of the jejunoileal MC, distinct for its serosanguineous fluid content. In conclusion, this case highlights the diagnostic challenge of MCs and illustrates the potential for successful management with a timely and multidisciplinary approach.