Endoscopic ultrasound-guided fine-needle aspiration for diagnosing a rare extraluminal duodenal gastrointestinal tumor

Duodenal gastrointestinal stromal tumors (GISTs) are extremely rare disease entities, and the extraluminal type is difficult to diagnose. These tumors have been misdiagnosed as pancreatic tumors; hence, pancreaticoduodenectomy has been performed, although partial duodenectomy can be performed if accurately diagnosed. Developing a diagnostic methodology including endoscopic ultrasonography (EUS) and fine-needle aspiration (FNA) has allowed us to diagnose the tumor directly through the duodenum. Here, we present a case of a 50-year-old woman with a 27-mm diameter tumor in the pancreatic uncus on computed tomography scan. EUS showed a well-defined hypoechoic mass in the pancreatic uncus that connected to the duodenal proper muscular layer and was followed by endoscopic ultrasound-guided fine-needle aspiration (EUS-FNA). Histological examination showed spindle-shaped tumor cells positively stained for c-kit. Based on these findings, the tumor was finally diagnosed as a duodenal GIST of the extraluminal type, and the patient underwent successful mass resection with partial resection of the duodenum. This case suggests that EUS and EUS-FNA are effective for diagnosing the extraluminal type of duodenal GISTs, which is difficult to differentiate from pancreatic head tumor, and for performing the correct surgical procedure.