Gallbladder anomalies vary, ranging from variations in size, site, anomalies of the duct system, and shape. Among these anomalies, an ectopic gallbladder, caused by a variation in location, is the most common [2]. The most common ectopic locations are (1) under the left hepatic lobe, (2) intrahepatic, (3) transverse, and (4) retroplaced (retrohepatic or retroperitoneal) [3]. In our case, the ectopic gallbladder was located on the ventral side of the common hepatic duct, and to the best of our knowledge, this location has not been reported previously.
There are several ways in which an ectopic gallbladder can lead to clinical uncertainty. For example, an ectopic gallbladder located away from the peritoneum may not instigate the typical peritoneal symptoms associated with acute cholecystitis, thereby delaying the diagnosis [4, 5]. However, the condition may be complicated, given that a floating gallbladder may also be predisposed to torsion, particularly if provoked by peristaltic action of nearby bowel segments. Moreover, ectopic gallbladders located beneath the left hepatic lobe are susceptible to herniation through the foramen of Winslow. For these reasons, it has been suggested that an ectopic gallbladder should be resected when found [6].
Ultrasonography, computed tomography, and radionuclide imaging are common modalities used for imaging-based diagnosis of an ectopic gallbladder [7]. However, an ectopic gallbladder can be left undetected on imaging studies, particularly in patients with a contracted gallbladder or in those with an incompletely distended gallbladder secondary to inadequate preoperative fasting. In our case, the ectopic gallbladder was small and located beside the common hepatic duct at the hilum of the liver; therefore, it could not be detected by preoperative examination. Ectopic gallbladders are usually diagnosed intraoperatively. Intraoperative complications are avoidable if the ectopic gallbladder is recognized early in the operation. However, delay in recognition of an ectopic gallbladder during surgery may lead to biliary complications, such as gallbladder rupture or biliary peritonitis [3].
Conversely, gallbladder agenesis, which we suspected preoperatively in our case, is another rare congenital anomaly with an incidence rate of 0.1–0.65%, and approximately 50% of these patients present with symptoms of biliary diseases [8]. The developmental abnormality of the biliary system results in an ectopic gallbladder and gallbladder agenesis. The liver, gallbladder, and biliary system begin to develop early in the fourth week of intrauterine life in the form of a ventral outgrowth from the caudal part of the foregut. This hepatic diverticulum is divided into two parts as it grows: one representing the primordium of the liver and the other representing the primordium of the gallbladder and cystic duct. By the seventh week of intrauterine life, vacuolation occurs, and the gallbladder and the cystic duct develop a lumen [9]. Failure of this developmental process at any stage results in agenesis of the gallbladder, whereas inappropriate migration of the gallbladder primordium results in an ectopic gallbladder [10]. In our case, the patient would have been diagnosed with gallbladder agenesis and the ectopic gallbladder would not have been detected had she not undergone surgery for CBD. Similarly, some previous reports of gallbladder agenesis might include cases with an ectopic gallbladder.
An ectopic gallbladder has been reported to be associated with congenital diseases such as congenital agenesis of the right lobe of the liver or duplication of the common bile duct [11, 12]; however, to the best of our knowledge, the association between an ectopic gallbladder and CBD has not been reported previously. Congenital biliary dilation is occasionally associated with an anomalous biliary tree. Specifically, an anomalous biliary tree may not be easily identified on preoperative imaging. Therefore, surgeons should be mindful of the possibility of anatomical abnormalities of the biliary tree during hepatobiliary surgery. In our case, while we suspected the absence of the gallbladder until halfway through the operation, meticulous exploration at the hepatic hilum revealed an ectopic gallbladder.