Case: A 59-year-old man, without prior medical history, presented with high-grade obstructive symptoms, including coffee-ground vomiting. CT revealed a pancreatic mass causing gastric outlet obstruction due to duodenal invasion. With partial encasement of the superior mesenteric vein and side branch of the superior mesenteric artery, the disease was deemed locally advanced, requiring neoadjuvant treatment. To facilitate oncological therapy, a bypass was indicated for which creation of an EUS-GE was elected.

The procedure was performed using a 20 × 10 mm electrocautery-enhanced Lumen Apposed Metal Stent (LAMS; Hot AXIOS™) and the Wireless Endoscopic Simplified Technique (WEST). Utilizing an oro-enteric catheter for enteric distention, the LAMS was correctly deployed without immediate adverse events. The patient resumed intake and was discharged after achieving clinical success.

Four days after, he was re-admitted with obstructive symptoms and a distended non-peritonitic abdomen. Laboratory findings were unremarkable. A CT scan confirmed LAMS patency but revealed a mesenteric "whirl sign" and caliber transition, diagnostic of acute mesenteric volvulus with closed-loop small bowel obstruction.

Emergency laparoscopy confirmed an intact EUS-GE with LAMS positioned 10-15 cm beyond the ligament of Treitz. However, a complete Petersen-type internal herniation of the small bowel through the mesenteric defect created by the gastrojejunostomy was found. After reduction, torsion of the efferent jejunal segment became apparent, but tissue appeared non-ischemic. To prevent recurrence, the Petersen space was closed and a distal side-to-side gastrojejunostomy in omega configuration was created. The postoperative course was favorable.

EUS-GE theoretically confers the same anatomical risk as surgical bypass procedures (e.g., Roux-en-Y gastric bypass): formation of a Petersen space, a mesenteric defect with a gateway for internal herniation and volvulus. The rarity of this complication suggests an unusual contributing mechanism in this patient. We hypothesize that herniation in this patient resulted from the combined effects of tumor-related distortion and the slightly more distal placement of the EUS-GE (~10-15 cm distal to Treitz), allowing for a larger Petersen space and more torsion.

Immediate detorsion, reduction and defect stabilization (closure of the Petersen space and creation of gastrojejunostomy performed here) yields favorable results. Whereas delayed diagnosis leads to bowel necrosis, perforation, and sepsis, carrying a mortality rate up to 30%.

Conclusion: Our case is a reminder that despite minimal invasiveness of EUS-GE, the resulting anatomical reconstruction might result in internal herniation with secondary mesenteric volvulus. Recurrent obstructive symptoms following EUS-GE should prompt early imaging to identify mesenteric abnormalities (the "whirl sign"). Early recognition and intervention are essential to prevent ischemic injury, morbidity and mortality risk associated with delayed management.