We present the case of a 58-year-old female patient with past medical history significant for severe obesity and gallbladder stones who was planned for bariatric surgery and cholecystectomy. Intraoperatively, an 3cm ovoid mass arising from the wall of the duodenal bulb was detected. Thus, only cholecystectomy was performed and bariatric surgery was postponed.
A post-operative endoscopic ultrasound (EUS) confirmed a well-defined, oval-shaped, hypoechoic heterogeneous lesion, with 25x10mm, involving the deep submucosa, the muscularis propria and the serosa (3rd, 4th and 5th layers) of the duodenal bulb and showing exophytic growth (Fig. 1A). This mass had a heterogeneous echo pattern with some vascularization (Doppler positive – Fig. 1B). An EUS-guided fine-needle biopsy (FNB; 22G, 2 passes) was performed (Fig. 1C).
Fig 1. EUS (transbulbar): hypoechoic heterogeneous lesion, involving the deep submucosa, the muscularis propria and the serosa (3rd, 4th and 5th layers) of the duodenal bulb wall (1A) and showing some vascularization (1B); EUS-FNB (1C).
Fig 2. Pathology: pancreatic acinar cells showing a positive reaction to the presence of trypsin (2A: H&E, 10x; 2B: Trypsin, x10).
Pathology revealed fragments of pancreatic exocrine parenchyma, with acinar cells showing the characteristic positive reaction to the presence of trypsin (Fig. 2). Thus, the diagnosis of duodenal ectopic pancreas was established.
Ectopic pancreas (EP), also designated as heterotopic pancreas, is a rare congenital condition defined by the presence of pancreatic tissue outside its typical location without anatomic or vascular connections to the orthotopic pancreas. [1,2]
EP mainly develops in the stomach, followed by the duodenum, jejunum, ileum and peritoneum. In the duodenum, it is usually found in the second portion, especially in the periampullary area, and less commonly in the duodenal bulb. 
EP is typically diagnosed incidentally during routine upper endoscopy and surgical explorations. Endoscopically, it appears as smooth bulge covered with normal mucosa, sometimes displaying the typical landmark of central umbilication. On EUS, it presents as a hypoechoic subepithelial lesion with indistinct borders, usually arising from the submucosa (3rd layer). Occasionally it may involve the muscularis propria and serosa. In half of cases, an anechoic ductal structure can be seen within the lesion. [1,2]
Although EP is foremost asymptomatic, it may present with a variety of nonspecific symptoms, such as epigastric pain, nausea, and vomiting.
Complications and carcinoma developing in an ectopic pancreatic tissue are exceedingly rare. Therefore, it does not require treatment unless symptomatic, and can almost always be dismissed in the absence of symptoms. [1,2]
Yet innocent, EP may mimic other subepithelial lesions, in particular gastrointestinal stromal tumors (GISTs) or neuroendocrine tumor (NETs), which harbor malignant potential and benefit from resection. Therefore, pathological diagnosis confirmation should be sought using standard forceps biopsy (“bite on bite” technique) and, preferably, EUS-fine needle tissue acquisition [4,5]
Susana Marques1, Miguel Bispo1, Mireia Castillo-Martin2, Ricardo Rio-Tinto1, Paulo Fidalgo1, Jacques Devière1,3