Our study showed that 2.5% of liver transplant donor candidates (8 out of 317) had circumportal pancreas. This result suggests that the prevalence of circumportal pancreas is not extremely low. This anomaly has not received adequate attention in preoperative imaging studies. If an aberrant pancreatic tissue is small, it may be difficult to spot during the surgical procedure. In addition, the degree of pancreatic fistula from a small aberrant pancreatic tissue may be subclinical if drainage tubes are placed appropriately.
The embryogenesis of the pancreas is complex. The ventral pancreatic primordium rotates and fuses with the dorsal pancreatic primordium. Circumportal pancreas may result from the higher fusion of both primordia above the level of the spleno-portal junction. Interestingly, in one case, the common hepatic artery ran through the pancreatic head. It may also result from higher fusion of the ventral and dorsal pancreatic primordia.
In one of the eight circumportal pancreas cases (12.5%), the main pancreatic duct (MPD) was seen behind the main portal vein (retroportal MPD). Retroportal MPD was reported in three of the eight previously reported circumportal pancreas cases (37.5%) [3, 4]. Awareness of this coexisting anomaly is important for pancreatic resection because of the substantial risk of pancreatic fistula [3]. Although the mechanism of the development of retroportal MPD is unclear, it may be related to the large size of aberrant pancreatic tissue (i.e. the large size of the ventral pancreas behind the main portal vein may increase the chance of a retroportal course of the Wirsung's duct).
In our series, two of the eight donor candidates with circumportal pancreas (25%) had variant hepatic arteries, and the prevalence of variant hepatic arteries was similar to that without circumportal pancreas (23.4%). This result suggests that there is no association between circumportal pancreas and variant hepatic arteries.
The differential diagnoses of circumportal pancreas may include peripancreatic lymphadenopathy and the inferior edge of the caudate lobe of the liver. Although we did not have surgical confirmation from liver transplant donor candidates, we believe that multiplanar reformatted (MPR) images obtained from the thin-section MDCT were sufficient to prove the presence or absence of circumportal pancreas.
In conclusion, circumportal pancreas is not extremely rare. Care should be taken regarding the presence or absence of circumportal pancreas in patients for whom pancreatic head resection is planned.