Gastric Adenocarcinoma and Adult Midgut Malrotation: A Rare Intraoperative Finding

Midgut malrotation (MM) is a congenital anomaly typically diagnosed in infancy, with incidental detection in adults being rare. Its association with gastric malignancy is exceedingly rare and may complicate surgical planning. We present a case of a 78-year-old woman with a history of hypertension, pacemaker implantation, and prior appendectomy who presented with a three-month history of early satiety, vomiting, diarrhea, and unintentional weight loss. Upper endoscopy revealed a deeply excavated ulcer in the lesser curvature, confirmed as a gastric adenocarcinoma. A staging CT scan did not show any metastases. The patient underwent elective open subtotal gastrectomy with Billroth II gastrojejunostomy. During jejunal limb preparation, the ligament of Treitz was found lateral to the second portion of the duodenum, consistent with MM. Correction of MM was not performed because the patient was asymptomatic, and the gastrectomy was completed without complications. Her postoperative course was uneventful. Histopathology confirmed an advanced diffuse-type gastric adenocarcinoma, and adjuvant chemoradiotherapy was proposed. This case highlights the importance of recognizing unexpected anatomical variants, such as MM, during oncologic gastric surgery. Individualized management allows safe intraoperative decision-making.