Internal hernias are an uncommon cause of intestinal obstruction, with left paraduodenal hernia being the most frequent of these. Computed tomography (CT) with contrast media is advantageous for the clinical workup of suspected paraduodenal hernias. Here, we report a case of an unusual paraduodenal sac formed by a peritoneal membrane between the transverse and the descending colon, which entrapped the proximal jejunum, causing intestinal obstruction. Preoperative CT demonstrated a cluster of jejunal loops between the stomach and pancreas, and showed that the inferior mesenteric vein was laterally displaced.