GDCs are a congenital malformation that can occur in the entire gastrointestinal tract, with a reported incidence of 1 in 4500 to 10,000 births [4]. In general, GDCs are almost twice as common in women, and 20% have coexistence of other intestinal duplications. GDCs have been reported to be caused by developmental abnormalities of the foregut, and the two most widely supported hypotheses are Bremer’s recanalization inhibition and McLetchie’s chordal separation [5]. Communication or fistulation between the GDC and true gastric lumen is very rare, and poorly differentiated epithelium in the GDC wall may lead to carcinogenesis [2]. Therefore, surgical resection is recommended for patients with GDC. In this patient, the remnant GDC observed by CT examination was initially thought to be a metastatic lymph node due to PDAC. However, MRCP revealed the remnant to be GDC. From our experience, when a capsulated low-density tumor is observed around the stomach during work-up for other diseases, GDC should be taken as the differential diagnosis.
On the other hand, PD is also a rare anatomical abnormality, and its frequency has been reported to be 6–10% in patients with a history of endoscopic retrograde cholangiopancreatography and in autopsy cases [6]. Pancreatic malformations can be classified into migration and fusion anomalies. Fusion anomalies include those in which the dorsal pancreatic bud (including the Santorini duct) and the ventral pancreatic bud (including the Wirsung duct) do not fuse properly, causing the pancreas to divide. When the primary channels of multiple pancreatic ducts are formed, PD can result [6]. In this case, preoperative CT and MRCP showed a bifurcation of the main pancreatic duct, a pancreatic tail dividing into two parts, and a connection from the ventral side of the main pancreatic duct to the GDC. The histopathological results of the resected specimen showed that the GDC was connected to the pancreatic duct of the PD. In this case, duplicated pancreas tails and peripheral pancreatic ducts were observed, however, the embryological mechanism of duplicated pancreatic tails with peripheral pancreatic ducts has not been clarified yet. The usual concept of PD is determined by the incomplete fusion of the Santorini duct and the Wirsung duct at the duodenal side; therefore, duplication of pancreatic ducts and patency of the minor duodenal papilla are typical features. The ventral pancreatic bud usually rotates and fuses at the caudal side of the dorsal pancreatic bud. However, it seemed that the ventral pancreatic bud fused to the cranial side of the dorsal pancreatic bud in this case. We hypothesized that the ventral pancreatic bud might overhang toward the cranial side during the rotation because the ventral pancreatic bud was drawn by the GDC. As a result, the Wirsung duct properly fused with the Santorini duct at the duodenal side. However, the peripheral side of the ventral pancreatic bud did not fuse; therefore, bifurcated pancreatic ducts and duplicated pancreatic tails were formed. From these embryological backgrounds, this situation is defined as inverted PD [7, 8].
In addition, PDAC appeared at the junction of the PD and the fistula of the GDC.
Duplicated stomach has been found to be continuous with the main pancreatic duct in 78% of cases [9]. Traverso et al. reported that recurrent pancreatitis may occur due to secretion inflow when the duplicated stomach is continuous with the main pancreatic duct [10]. There are some reports of cystic carcinogenesis in pancreatic-associated GDCs, however, there has been only one reported case of PDAC with pancreatic-associated GDC, reported by Chiu et al. [11]. Furthermore, there have been no reports of cases involving PD. PD itself may have the potential to induce hepatobiliary malignancy or intraductal papillary mucinous neoplasms due to continuous stimulation by the pancreatitis [12, 13]. It is suggested that recurrent pancreatitis in pancreatic-associated GDCs may be related to mucus inflow or hemorrhage from the cyst to the communicating pancreatic duct [14]. Due to the risk of malignant degeneration of the cyst and pancreas, it is necessary to consider total resection of the pancreas and cysts rather than cyst drainage. As for this case, there were no risk factors for PDAC, such as diabetes mellitus or a history of abdominal pain due to pancreatitis or alcohol abuse. However, the patient may have had subclinical recurrent chronic pancreatitis due to increased risk of pancreatitis caused by PD and secretion inflow from the GDC. It is possible that the recurrent chronic pancreatitis may have triggered the development of PDAC at the junction of the pancreatic duct.