IPMNs account for 7-35% of all the cystic neoplasms of the pancreas in published surgical series [14
]. In contrast to patients with serous cystic neoplasms (SCN) or mucinous cystic neoplasms (MCN), patients with IPMN tend to be older, with a mean age at presentation of approximately 65 years. In the differential diagnosis of IPMN MCN and pancreatic intraepithelial neoplasia (PanIN) must be included [16
]. MCNs usually can be distinguished by the lack of pancreatic ductal structures and their characteristic ovarian-like stroma. Distinction of IPMNs from PanINs may be more difficult and has been the subject of an international consensus conference in August 2003 [17
]. While IPMNs are of macroscopically visible size, PanINs are microscopic findings involving ducts less than 5 mm [17
]. Moreover, IPMNs often express the mucin MUC-2, while PanINs usually express MUC-1.
Heterotopic pancreas, on the other hand, is defined as pancreatic tissue that lacks direct or vascular connection to normal pancreas [18
]. In autopsy series, the prevalence of this congenital condition ranges from 0,55% to 13,7% [19
]. Clinically, pancreatic heterotopia is observed in one out of 500 upper abdominal operations [20
]. Pearson et al [12
] reviewed 589 cases of heterotopic pancreas, and reported the frequencies of this disorder as follows: 30% in the duodenum, 25% in the stomach, 15% in the jejunum, 3% in the ileum and 6% in Meckel's diverticulum. Particularly in the stomach, heterotopic pancreatic tissue predominantly develops in males between 30 and 50 years of age. The majority of cases identified in the stomach are submucosal tumors, located in the antrum [21
The presence of heterotopic pancreas is usually asymptomatic, but it is capable of producing symptoms, depending on its location and size [22
]. Several cases have been reported in the literature presenting as gastric outlet obstruction, small bowel obstruction, upper gastrointestinal bleeding or obstructive jaundice [23
]. Adenocarcinoma, islet cell tumors and cystic tumors have also been reported in heterotopic pancreas [19
In the literature, there are few reported cases of malignant change of ectopic gastric pancreas [30
]. The majority of these cases represent adenocarcinoma, while papillary mucinous neoplasia, of whatever histologic subtype, has been reported in only one case so far [13
]. The present case is the first reported with the unique characteristic of simultaneous existence of IPMN (of the mixed pancreatic duct type) and IPMN or PanIN of the heterotopic gastric pancreatic tissue. Our case satisfies the minimal diagnostic criteria for tumors that arise in heterotopic pancreatic tissue initially proposed by Guillou and colleagues [29
] which state that: i. the tumor must be found within or close to the ectopic pancreas, ii. direct transition between pancreatic structures and carcinoma must be observed (ie duct cell dysplasia or carcinoma in situ), iii. the non-neoplastic pancreas must comprise at least fully developed acini and ductal structures, and iv. direct extension or metastasis from an other site must be excluded.
The differential diagnosis in this case (as regards the ectopic gastric pancreatic tissue) includes low-grade intraepithelial neoplasia and small IPMN. As previously emphasized such distinction is impossible at times and currently is based on size and macroscopic appearance [32
]. Since the lesion described was noted on gross inspection of the surgical specimen, we believe that the designation of intraductal papillary mucinous neoplasm would be more appropriate. Moreover, the papillary excrescences are larger than those typically seen in PanIN.
The preoperative diagnosis of heterotopic pancreas is challenging despite the advances in imaging technology. Heterotopic pancreas usually presents in upper gastrointestinal series as a well-delineated submucosal filling defect with a central indentation [20
]. Endoscopically, the lesion is seen as a submucosal tumor with a central umbilication. The CT imaging of an ectopic pancreas enhances brightly as an orthotopic pancreas [29
Given its clinically insidious course, heterotopic pancreas is usually an incidental finding, either intraoperativelly, or during radiographic or endoscopic examination of the upper gut. When found at the time of laparotomy (as in our case), local excision, with or without frozen section, rather than radical resection is the preferred way of treatment [25
]. Potentially, however, the documentation of underlying malignancy based on the implemented frozen section analysis, sets the dilemma of performing a more radical surgical treatment in order to prevent re-operation or diagnostic difficulties.