Anatomical variations of the cystic duct

Anatomical variations of the cystic duct are usually of no clinical significance, occurring in 18%-23% of cases[4]. However, unrecognized variant anatomy can be a source of confusion on imaging studies. In addition, the cystic duct may be involved in a wide variety of both primary and secondary disease processes. The rate of injury varies in the medical literature from 0% to 1%[5]. The following are some of the cystic duct variations found: (1) the cystic and common hepatic duct are in parallel; (2) low confluence of the cystic duct[2]; (3) insertion of the cystic duct in the left and right hepatic ducts, and bifurcation of the left and right hepatic ducts[2]; (4) anterior, posterior spiral types of insertion of the cystic duct on the left side of the common hepatic duct; (5) parahepatic duct insertion into the cystic duct; (6) absent or short cystic duct (length <> 5 mm; (8) double cystic duct[6,7]; (9) right hepatic duct emptying into the cystic duct[8]; and (10) hepaticocystic duct[9], a very rare congenital abnormality in which the common hepatic duct enters the gallbladder. The left, right, and common hepatic ducts are all defective, with the cystic duct draining the entire biliary system into the duodenum.
Multiple modalities permit depiction of the normal anatomy, as well as disease processes of the cystic duct, including CT, PTC, ERCP, intraoperative cholangiography and MRCP. Although visualization of the dilated cystic duct is possible with US and CT, the normal-caliber cystic duct may be difficult to detect with these techniques[10]. In our first case, CT demonstrated minimal intrahepatic ductal dilatation, but failed to show low insertion of the cystic duct, as was revealed by surgery. In this case, the low insertion of the cystic duct was misdiagnosed as gallbladder and bile duct calculi. However, in the second case, ERCP showed a long cystic duct with a narrow and in-curved lumen. An anomalous cystic duct was diagnosed before surgery. Anatomical variation is readily identified at ERCP. In clinical practice, if the patient presents with intermittent non-colic right upper abdominal pain, and ultrasound, CT and endoscopy eliminate choledocholithiasis, tumor and peptic ulcer, then a narrow-winding cystic duct should be considered. ERCP is extremely helpful in diagnosis. Recent studies have demonstrated that MRCP may provide a non-invasive alternative to ERCP and PTC in diagnosis of anomalous cystic ducts[11]. Taourel and colleagues[12] evaluated the accuracy of MRCP in the diagnosis of anatomic variants of the biliary tree in 171 patients. MRCP demonstrated a cystic duct in 126 patients (74%), including low cystic duct insertion in 11 (9%) and a parallel course of the cystic and hepatic ducts in 31 patients (25%). These findings suggest that accurate preoperative assessment is very useful in providing a surgical treatment plan in addition to confirming diagnosis. During cholecystectomy, to avoid biliary tree injury, it is important to identify the common hepatic-cystic duct junction. Misidentification of the cystic duct can lead to postoperative complications. In particular, attention should pay to low medial insertion of the cystic duct because this anatomical variant may lead to misdiagnosis on imaging, and thus affect therapeutic intervention, as was seen in our first case.
A limited literature review of bile duct variation has shown that the aim of most surgeons is to identify whether there are bile duct stones. With respect to the accidental discovery of bile duct variation, it is not the nature of the variation itself but rather the existence of the bile duct variation that is the most important factor in the prevention of bile duct injury. Most injuries to the cystic duct usually occur when it runs parallel to the common bile duct and is encased in a common sheath, so that separation between the ducts is not readily apparent at surgery. T-tube placement in the cystic duct remnant is usually of no consequence; however, there may be a difficulty if retained common duct stones are present, and stone removal via the T-tube is attempted. In such cases, access to the bile duct is via a tract that enters the cystic duct, and manipulation and extraction must occur via the cystic duct across the valves of Heister. Stone extraction is more difficult or may be impossible via this route[13]. Suspicion should be raised if the cystic duct is of an unusually large calibre. Intraoperative cholangiography should be used in case of doubt and, in unusual circumstances, cholangiography can be performed via the gallbladder to aid in the identification of the cystic duct as well as the common bile duct.
In conclusion, the cystic duct may be involved in a variety of anatomical variations. Diagnostic accuracy relies on a clear understanding of the normal anatomy and anatomical variants of the cystic duct, and imaging features of calculous disease.

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