Reverse-orientation small-bowel anastomosis causing functional obstruction mimicking afferent loop syndrome after pancreaticoduodenectomy in a patient with prior right hemicolectomy: a case report

Afferent loop syndrome (ALS) after pancreaticoduodenectomy (PD) is typically caused by mechanical obstruction. Reverse-orientation small-bowel anastomosis is an exceptionally rare complication of complex bowel reconstruction that causes functional obstruction through retrograde peristalsis despite a structurally patent bowel lumen, thereby closely mimicking ALS and making the diagnosis particularly challenging. We report a rare case highlighting its characteristic radiological findings and diagnostic pitfalls that may facilitate earlier recognition. A 72-year-old man with a history of right hemicolectomy for transverse colon cancer underwent pancreaticoduodenectomy with superior mesenteric vein reconstruction for locally recurrent disease invading the pancreas and mesenteric vessels. Postoperatively, he developed persistent intolerance to oral intake, high-output bilious drainage, and afferent limb dilatation, initially suggesting delayed gastric emptying or ALS. Despite repeated imaging showing a structurally patent bowel without a definite transition point, the diagnosis remained elusive. Dynamic fluoroscopy demonstrated antiperistaltic contrast propulsion, and computed tomography revealed the “reversed jejunal artery sign,” establishing the diagnosis of reverse-orientation small-bowel anastomosis. Revisional surgery restored normal bowel orientation, resulting in complete symptom resolution and recovery of oral intake. Reverse-orientation small bowel anastomosis is a rare but important cause of functional obstruction after PD that may be overlooked because the bowel remains structurally patent. Recognition of the “reversed jejunal artery sign” on computed tomography, antiperistaltic contrast propulsion on fluoroscopy, and the operative circumstances predisposing to loss of bowel orientation may facilitate earlier diagnosis and timely surgical correction.