A duodenal gastrointestinal stromal tumor mimicking a pancreatic neuroendocrine tumor: a case report

Duodenal gastrointestinal stromal tumors (dGISTs) are extremely rare, and account for < 5% of all gastrointestinal stromal tumor (GIST) cases [1, 2]. A biopsy is considered essential for the diagnosis of GIST, but endoscopic ultrasound fine-needle aspiration (EUS-FNA) may not be possible in some situations. dGISTs may develop extramurally, extensively, in a stem-like fashion, or may be embedded in the pancreatic parenchyma, complicating the distinction from duodenal or pancreatic primary hypervascularized enhancing tumors on computed tomography (CT) and the selection of the appropriate surgical technique. We present a case of pancreaticoduodenectomy for a dGIST that was difficult to differentiate from a pancreatic neuroendocrine tumor (pNET).

Case presentation

A 44-year-old Japanese woman had anemia identified by a medical examination in the workplace. Six months later, she was hospitalized with lightheadedness. Laboratory data revealed a hemoglobin level of 4.1 g/dL. She was admitted to our hospital after receiving a transfusion and ferrotherapy. Results of all other laboratory studies were within the normal range (Table 1). She had no pregnancies or children. Her father had died of pancreatic cancer. She had no significant past medical history and no smoking history, and she did not consume alcohol. On admission, her heart rate was 60 beats per minute, her blood pressure was 130/70 mmHg, and her temperature was 37.1 °C. There were no other findings on physical and neurological examination. Contrast-enhanced CT showed a 30-mm mass that was heterogeneously enhanced at the margins, and the origin of the tumor, either the duodenum or the head of the pancreas, was unclear (Fig. 1a, b). Positron emission tomography (PET) showed a maximum standardized uptake value (SUVmax) of 16.7 in the tumor (Fig. 2a, b). Upper gastrointestinal endoscopy revealed bulging accompanied by erosion and redness in part of the duodenal bulb (Fig. 3a). A mucosal biopsy was not diagnostic. EUS demonstrated a 40 × 35 mm² mass with cystic and solid components in the head of the pancreas (Fig. 3b). EUS-FNA was difficult to perform because a pulsating blood vessel was present in the region to be punctured (Fig. 3c). These findings led to the diagnosis of pNET invasion to the duodenum. The patient underwent pancreaticoduodenectomy. Macroscopic findings were a 4.0 × 2.3 × 3.9 cm³ mass that occupied the first part of the duodenum, that broke down on the mucosal surface to form an ulcer, and that developed extrusive growth toward the pancreatic head (Fig. 4). Microscopic findings were that the tumor was made up of spindle-shaped cells, including nine mitotic figures per 50 high-power fields, immunohistochemically positive for c-Kit and CD34 (Fig. 5). The tumor was diagnosed as a high-risk dGIST on the basis of the Fletcher classification or modified Fletcher classification. The patient was treated with adjuvant imatinib, and she has not developed a recurrence over a 2-year period.

In this case, a hypervascularized tumor in the pancreatic head region was discovered owing to anemia, but biopsy was difficult, and a pancreaticoduodenectomy with lymph node dissection was performed on the basis of suspicion of pNET on CT. Postoperative pathological examination revealed a primary dGIST, and radical surgery with partial resection could be considered.

GISTs are relatively common mesenchymal tumors that occur predominantly in the stomach (60–70%) and small intestine (25–35%) [3]. dGISTs are rare lesions, constituting 30% of primary duodenal tumors and less than 5% of all GISTs [4]. On CT, dGISTs appear as heterogeneously enhanced hypervascularized masses [5, 6]. When extraluminal dGIST growth extends to the head of the pancreas, the tumor is difficult to differentiate from other well-vascularized tumors. pNETs appear as circumscribed solid masses that displace surrounding structures and are often hyperattenuating on arterial and venous phase images [7]. Since dGISTs and pNETs may have similar features on imaging, these two lesions may be misdiagnosed. After searching the PubMed database with the search terms “duodenal GIST” and “pancreas tumor,” we found 13 cases of dGIST that were difficult to differentiate from pancreatic tumors preoperatively, including our case [8‐19]. In four cases, EUS-FNA was performed, three of which were diagnosed as GIST [10, 14, 15, 17]. EUS-FNA is the only way to obtain a preoperative pathological diagnosis. Generally, the specificity of EUS-FNA is reported to be 100%, and the sensitivity is 84% [20‐22]. However, the rate of adverse events related to the EUS-FNA procedure is reportedly 0.98–3.4%, with events including acute pancreatitis, bleeding, infection, and duodenal perforation [23‐26]. Among the previous reports, 6 of the 13 cases had symptoms associated with gastrointestinal bleeding [8, 11, 13, 18]. These included the cases for which EUS-FNA was not performed because of concerns about possible recurrent bleeding [8], and surgery was performed immediately after blood transfusion [19].

In our case, the tumor contained a pulsatile artery, and the risk of bleeding from EUS-FNA was high. Popivanov et al. [27] reported 549 cases of resected dGIST, and their analysis revealed that in contrast to the other localizations, dGIST has upper gastrointestinal bleeding as the most frequent manifestation. In such cases, pancreatoduodenectomy was performed in an emergency setting due to life-threatening bleeding. For GISTs, R0 resection with 1–2 cm clear margins is a sufficient treatment, and lymph node dissection is not recommended owing to the low incidence of lymphatic metastases [28]. On the other hand, surgical resection with regional lymph node dissection is the only curative treatment for pNETs [29]. Thus, it is important to make an accurate diagnosis before surgery. There was one case report in which the diagnosis of dGIST was made from intraoperative frozen tissue [11]. Although biopsy of the intraperitoneal cavity has a high risk of peritoneal dissemination and is contraindicated, intraoperative histology was assessed after complete tumor resection in this report. This method may be useful when a change in surgical technique is considered. Yanming et al. reported that the postoperative prognosis of dGIST is promising and is affected mainly by tumor factors, and the choice of surgical approach should depend on the anatomical location and tumor size [30]. If a case shows detachment around the tumor, partial resection of the duodenum and intraoperative histological diagnosis is considered possible. In our case, the tumor was misdiagnosed as a pNET preoperatively, and the patient therefore underwent a pancreaticoduodenectomy with lymph node dissection. Even if a dGIST had been diagnosed before surgery, because detachment of the boundary between the dGIST in the first portion of the duodenum and the pancreas head had a higher risk of pancreatic juice leakage and peritoneal dissemination, pancreaticoduodenectomy would have been considered appropriate. However, lymph node dissection would not have been necessary.

Extraluminal dGISTs are rare and mimic pNETs. EUS-FNA is useful for preoperative diagnosis, but it is not applicable in some cases. When resecting a mass in the pancreatic head region, intraoperative diagnosis based on a completely resected specimen of the tumor may be useful for modifying the surgical technique, considering the possibility of dGIST.