Imaging anatomy

The normal cystic duct connects the gall bladder to the common hepatic duct to form the common bile duct, and is considered the most important structure to be identified during cholecystectomy.[1] The normal cystic duct usually measures 4-6 cm in length and contains concentric folds known as the spiral valves of Heister.[2] Cystic ducts shorter than 2 cm can also be found, which can present a significant challenge in the dissection and placement of clips during laparoscopic cholecystectomy. The diameter of the cyst duct ranges from 1 to 5 mm. The cystic duct usually joins the extrahepatic bile duct approximately half-way between the porta hepatis and ampulla of vater, commonly to its medial aspect.[2] The triangle of Calot is an important landmark in identifying the cystic artery and the cystic duct [Figure 4]. The boundaries of the Calot’s triangle consist of the common hepatic duct medially, cystic duct laterally, and inferior margin of the liver superiorly.[1]

Figure 4

Line diagram depicting the triangle of Calot (shaded area). The boundaries are formed medially by the common hepatic duct, laterally by the cystic duct, and superiorly by the inferior margin of the liver.

On gray-scale ultrasonography, the normal cystic duct is seen only in 50% of the patients as an anechoic tubular structure connecting the gall bladder and the extrahepatic duct.[2] The normal cystic duct is usually not visible on CT scans and may sometimes be seen as a low attenuating tubular structure with a thin enhancing wall.[2]

Magnetic resonance cholangiopancreatogram (MRCP) can routinely demonstrate entire course of the normal cystic duct. A normal cystic duct appears bright on T2 weighted MR sequences and dark on T1weighted MR sequences. Sometimes cystic duct may appear bright on T1 weighted sequences when it contains concentrated bile.[2]

The gold standard method of demonstrating biliary tree is direct cholangiography, where injection of contrast is performed with percutaneous transhepatic cholangiography, endoscopic retrograde cholangiopancreatography, or T tube cholangiography.[2]

During cholecystectomy, a variable length of the cystic duct is left as a remnant. Usually, a cystic duct remnant measuring 1-2 cm in length is left, although remnants can be seen up to 6 cm in length. Complications associated with the remnant cystic duct are retained stones in cystic duct, bile leakage, stricture, fistula formation, dilatation of the cystic duct remnant, amputation neuromas, and suture granuloma of the cystic duct. Cystic duct mucocele is a rare complication, where the remnant of the cystic duct is distended with mucus.[2]

Following cholecystectomy, the cystic duct caliber in an asymptomatic patient is often the same as in a normal patient. The caliber of the normal remnant measures approximately 4 mm and the length is 5-25 mm. A cystic duct measuring > 5mm is considered abnormal (Dilated). The terminal end of the cystic duct remnant is described as resembling a “leaf bud” in normal post-cholecystectomy patients. When the remnant is pathologically dilated, it is described as having the appearance of a “flashlight bulb”.[3] The dilatation or the pouch formation of the cystic duct remnant is thought to be due to an inflammatory reaction.[3] In 1936, Beye reported 14 cases of dilated cystic ducts as “reformed gall bladder” and concluded that the symptoms are due to this remnant cystic duct.[4] It is important to identify these cystic duct remnants as they act as a cul-de-sac with a potential source of infection and are frequently associated with the presence of stones.[5] Brown stated that all the resected cystic duct remnants show evidence of chronic inflammation without evidence of neoplastic changes. [Brown MJ, Diseased cystic duct remnant: (Presented at the 16th annual meeting of the central surgical association, Montreal, Feb 20 1959).]