Most gastrinoma occurs in the so-called gastrinoma triangle, and ectopic gastrinoma is rare. We report a case of possible primary gastrinoma of the lesser omentum. A 74-year-old woman who previously suffered twice from the duodenal ulcer perforation and underwent distal gastrectomy was referred for high serum gastrin. Intravenous glucagon injection caused a paradoxical increase in serum gastrin. Computed tomography and magnetic resonance imaging showed a tumor in the lesser omentum close to the gastric remnant. An intraarterial glucagon injection test showed the tumor to be a gastrinoma fed by the left gastric artery. We resected the gastric remnant with the tumor, which was diagnosed histologically as an endocrine tumor secreting gastrin. No increase in serum gastrin was observed in intraoperative or postoperative intravenous glucagon injection tests. The woman shows no signs of recurrence and her serum gastrin is within the normal range in the 2 years since surgery. The glucagon provocative test was thus useful in diagnosis and treatment of possible primary gastrinoma in the lesser gastric curvature.
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