EPT is a rare entity; however, its actual incidence in the gallbladder is unidentified, as a lack of clinical symptoms can complicate the diagnosis (5). It can occur anywhere, but the most common locations are the stomach (27.5%), duodenum (25.5%), colon (15.9%), jejunum, and spleen (6). By contrast, the presence of EPT in the gallbladder, lung mediastinum, liver, mesentery, and ileum is considered extraordinary (2, 7). EPT can be diagnosed in any age group, but most cases are between 40-60 years old. Albeit the male-to-female ratio of any other type of EPT is 3:1, there is a female predominance, specifically for EPT in the gallbladder, which may be due to the fact that cholecystitis-related cholecystectomies are more prevalent in women (2, 8). The etiologies of EPT are still unclear, but three hypotheses about its origin have been proposed. The first theory, which is widely accepted, suggests that EPT separates from the primitive pancreas gland during the rotation of the gastrointestinal tract in the embryogenic period. The second theory suggests that the longitudinal growth of the intestine from the lateral budding of the rudimentary pancreas tissue while penetrating the intestinal wall causes the irregular transportation of the pancreatic tissue (9, 10). The third theory supports that abnormalities in the notch signaling system can result in changes in different foregut endoderm tissue during embryogenesis (11). Jean Schultz first described the heterotropic pancreas in the 18th century; however, the first classification was made by Von Heinrich et al. in 1909, which was later modified by Fuentes in 1973 that consisted of four types (12):

According to what is mentioned above, this case is compatible with type three (figure1-3).

These ectopic pieces of tissue macroscopically can appear as an exophytic mass, similar to polypoid lesions, or as a nodule with a yellow-colored appearance with sizes varying from a few millimeters to even 4cm (13). Still, they are generally asymptomatic and only discovered histopathologically. However, in some cases, it can cause various nonspecific symptoms, depending on the location. Symptoms can include jaundice if obstructing bile ducts or biliary colic-like symptoms (e.g., right upper quadrant pain, anorexia, nausea, and vomiting after meals); nevertheless, such symptoms presumably result from simultaneous lithiasic cholecystitis. Other conditions can be derived from EPT, such as cholelithiasis, acute or chronic cholecystitis, or carcinoma (2, 10).

As Sato et al. reported that pancreatic enzymes (amylase and lipase) secreted from EPT in the gallbladder could impact its mucosa leading to gallbladder dysplasia and carcinoma. Therefore, cases with EPT in the gallbladder must undergo cholecystectomy as a definite treatment preventing any potential malignant transformation. Moreover, EPT can potentially cause the same pathologies as typical pancreatic tissue, which includes cysts, pseudocysts formation, abscess, and acute or chronic pancreatitis (14, 15).

Diagnosing EPT in the gallbladder before and during an operation is impossible. Preoperative radiologic evaluation (ultrasound or computed tomography scan) usually cannot detect EPT in the gallbladder; neither this case did (16). Therefore, only a precise histopathologic examination can provide a definite diagnosis; consequently, it’s essential for anatomical pathologists to be aware of this uncommon presentation of EPT in gallbladder to discriminate it from a masquerading malignancy.