CBD cysts are classified into five categories as described by Todani et al. Type I is cyst of the extrahepatic bile duct only; type II is a supraduodenal CBD diverticulum; type III is a choledochocele; type IV refers to multiple dilatations in the intra- and extrahepatic bile ducts; type V is single or multiple cysts in the intrahepatic bile ducts without extrahepatic bile ducts, which is known as Caroli disease [2]. Type VI biliary cysts are rare and are not included in the Todani classification. A very limited number of reports in the literature mainly consist of single case reports, and to our knowledge, only one review has been done [4].
The most accepted theory for the development of CBD cysts is APBDJ, which occurs in approximately 40% of cases [5]. In the cases of APBDJ, the CBD and pancreatic ducts merge more proximally than normal, opening to the Oddi sphincter. This causes reflux of pancreatic enzymes to the CBD and leads to weakening and cystic dilatation in the CBD wall. However, not all CBD cysts are accompanied by APBDJ, and sometimes APBDJ can be seen when CBD cysts are absent. This situation suggests that, more than one mechanism is responsible for the development of CBD cysts [6, 7]. Amarjothi et al. argued that cystic duct cysts may result from a combination such as APBDJ, acute angulation, and cystic duct–CBD connection with a wide opening [8]. However, in most cases reported in the literature and in our case, APBDJ, angulation, and wide opening of the cystic duct to the CBD were not observed. More research is needed to evaluate other factors that may be responsible.
Clinical symptoms of cystic duct cysts are often similar to other CBD cysts. They can also be asymptomatic and detected incidentally. When symptomatic, they often occur with RUQ and epigastric pain. Apart from this, they can occur with complications such as jaundice, cholangitis, and gallstone disease, depending on the size of the cyst and the pressure effect it creates [9]. Although the most feared complication is cholangiocarcinoma arising from the cyst itself, it is rare [10]. In our case, there was intermittent recurrent RUQ pain, but no signs of complication were detected.
Due to their rarity, type VI biliary cysts are often not diagnosed preoperatively or are misdiagnosed. Most known cases were diagnosed intraoperatively [5, 6, 10]. Type VI biliary cysts can be seen in a variety of ways. Fusiform or saccular dilatation can be seen in the cystic duct, without any dilatation in other bile ducts, or fusiform cystic duct dilatation can be observed with a varying relationship between dilated CBD and the cyst [10]. Radiological imaging is very useful in preoperative diagnosis. US is often the first choice method. A non-vascular dilated cystic lesion is detected at the level of the porta hepatis. In such a case, an attempt should be made to show the relation of the cystic lesion to the bile ducts, gallbladder and CBD. However, US is operator-dependent, and it may not be possible to demonstrate these relationships in the presence of inflammatory conditions. Endoscopic retrograde cholangiopancreaticography (ERCP) is the gold standard in diagnosis, but it is invasive. Apart from this, it requires sedation, and there are risks of complications such as biliary sepsis, cholangitis, pancreatitis, perforation, and contrast allergy. MRCP, which is noninvasive and radiation-free, can be used as an equivalent to ERCP for diagnosis with excellent resolution in demonstrating the biliary tract. MRCP helps to detect the localization of the cyst, its relationships, the presence of possible APBDJ, and complications [8, 10]. ERCP is indicated when MRCP is insufficient or when a therapeutic procedure is required. In our case, the cystic lesion was detected by US, but the localization relationships could not be determined clearly. On MRCP, the diagnosis was made accurately, and there was no need for ERCP.
Management of type VI biliary cysts is guided by morphology [1, 8]. Early and accurate radiological diagnosis is very important to prevent complications and to choose an appropriate surgical method. In case of a narrow connection to the CBD, cyst excision and cholecystectomy are sufficient. However, in cases where there is a wide connection to the CBD, hepaticojejunostomy should be performed in addition to the above procedures [8, 10]. In our case, since there was a narrow connection between the cystic duct and the CBD, cholecystectomy and cyst excision were performed laparoscopically, and the patient was discharged without any problem after surgery.
