(Radiographics. 2001;21:3-22.)
© RSNA, 2001
The Cystic Duct: Normal Anatomy and Disease Processes1
Mary Ann Turner, MD and
Ann S. Fulcher, MD
1 From the Department of Radiology, Medical College of Virginia, 401 N 12th St, Box 980615-MCV Station, Richmond, VA 23298. Presented as an educational exhibit at the 1999 RSNA scientific assembly. Received March 10, 2000; revision requested April 11 and received June 15; accepted June 29. Address correspondence to M.A.T. (e-mail: maturner@hsc.vcu.edu).
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Abstract
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The cystic duct can be depicted with a variety of imaging modalities but is optimally visualized with direct cholangiography or magnetic resonance cholangiopancreatography. Nevertheless, unrecognized anatomic variants of the cystic duct may cause confusion on imaging studies and complicate subsequent surgical, endoscopic, and percutaneous procedures. Primary entities involving the cystic duct include calculous disease, Mirizzi syndrome, cystic duct–duodenal fistula, biliary obstruction, neoplasia, and primary sclerosing cholangitis. The cystic duct may also be secondarily involved by adjacent malignant or inflammatory processes. Postoperative alterations are seen after liver transplantation or cholecystectomy when a portion of the cystic duct is left behind as a remnant. Recognized postoperative complications include retained cystic duct stones, cystic duct leakage, and malposition of T tubes in the remnant. Pitfalls encountered in cystic duct imaging include pseudocalculous defects from overlap of the cystic duct and common bile duct, underfilling of the cystic duct during direct cholangiography, and admixture defects at the cystic duct orifice. Pseudomass or pseudotumor defects may result from an impacted cystic duct stone or from a tortuous, redundant cystic duct. Familiarity with the imaging appearance of the normal cystic duct, its anatomic variants, and related disease processes facilitates accurate diagnosis and helps avoid misinterpretation.
Index Terms: Bile duct radiography, 76.1222, 76.1224, 76.1226 • Bile ducts, anatomy, 76.92 • Bile ducts, calculi, 76.28 • Bile ducts, CT, 76.1211 • Bile ducts, diseases, 76.28 • Bile ducts, MR, 76.12142 • Bile ducts, neoplasms, 76.32, 76,331 • Bile ducts, stenosis or obstruction, 76.28 • Bile ducts, US, 76.1298
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LEARNING OBJECTIVES FOR TEST 1
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After reading this article and taking the test, the reader will be able to:
- Identify the normal and variant anatomy of the cystic duct.
- Identify the imaging features of disease processes of the cystic duct such as calculous disease, primary sclerosing cholangitis, and malignancy.
- Recognize postoperative alterations and complications involving the cystic duct as well as common diagnostic pitfalls.
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Introduction
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Although much has been written about the normal anatomy and related diseases of the gallbladder and biliary tract, few studies have focused on the cystic duct. The cystic duct connects the gallbladder to the extrahepatic bile duct. Anatomic variants of the cystic duct are common and are usually of no clinical significance. However, unrecognized variant anatomy can be a source of confusion on imaging studies. In addition, the cystic duct may be involved by a wide variety of both primary and secondary disease processes.
Multiple modalities permit depiction of the normal anatomy as well as disease processes of the cystic duct, including ultrasonography (US), computed tomography (CT), direct cholangiography (percutaneous transhepatic cholangiography [PTC], endoscopic retrograde cholangiopancreatography [ERCP], T tube and intraoperative cholangiography) in addition to magnetic resonance (MR) imaging, MR cholangiopancreatography, and cholescintigraphy. Although visualization of the dilated cystic duct is possible with US, CT, or cholescintigraphy, the normal-caliber cystic duct may be difficult to detect with these techniques. The small caliber of the cystic duct and its tortuosity make detection difficult with US and axial CT, and cholescintigraphy is further limited by low resolution. Optimal visualization of the cystic duct requires direct cholangiography or MR cholangiopancreatography, both of which depict the cystic duct in the coronal plane along its long axis. The cystic duct is seen at direct cholangiography or MR cholangiopancreatography in virtually all cases. At direct cholangiography, injection of contrast material into the biliary ductal system opacifies and outlines the long axis of the cystic duct; fluoroscopy with rotation of the patient projects the cystic duct away from the common bile duct, allowing visualization of the entire cystic duct. Similarly, the capacity of MR cholangiopancreatography to provide coronal images and to orient the angle of image acquisition along the long axis of the cystic duct optimizes duct visualization. Interventional procedures involving the biliary tract may be complicated by the presence of confusing imaging patterns related to the cystic duct.
In this article, we review the normal anatomy of the cystic duct as well as anatomic variants, related pathologic processes, postoperative alterations and abnormalities, and diagnostic pitfalls.
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Normal Anatomy
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The cystic duct attaches the gallbladder to the extrahepatic bile duct; its point of insertion into the extrahepatic bile duct marks the division between the common hepatic duct and the common bile duct (Fig 1). The cystic duct usually measures 2–4 cm in length and contains prominent concentric folds known as the spiral valves of Heister. The cystic duct frequently exhibits a tortuous or serpentine course. The normal diameter of the cystic duct is variable, ranging from 1 to 5 mm.
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Figure 1. Drawing illustrates the normal biliary tract. The cystic duct (arrows) connects the gallbladder to the extrahepatic bile duct and usually enters from the right approximately halfway between the porta hepatis and the ampulla of Vater. It also contains the valves of Heister.
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The cystic duct usually joins the extrahepatic bile duct approximately halfway between the porta hepatis and the ampulla of Vater. However, the point at which the cystic duct joins the extrahepatic bile duct is variable, ranging from high at the level of the porta hepatis to low at the level of the ampulla.
The cystic duct enters the extrahepatic bile duct from the right lateral aspect in 49.9% of cases, from the medial aspect in 18.4%, and from an anterior or posterior position in 31.7%. It usually runs parallel to the extrahepatic bile duct for a short distance and may spiral around the bile duct to insert medially. The cystic duct has a parallel course relative to the extrahepatic bile duct in 10.6% of patients and varies in length from 1.5 to 9.5 cm (mean, 3–4 cm). Of these parallel cystic ducts, 17% have a spiral course (1–4).
At direct cholangiography, whether the injection is performed with PTC, ERCP, surgical cholangiography, or T tube cholangiography, the normal cystic duct usually fills with adequate injection of contrast material into the biliary tract and optimal patient positioning (Fig 2). Absence of filling of the cystic duct at ERCP is usually related to patient positioning rather than cystic duct obstruction (4,5).
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Figure 2. Normal cystic duct anatomy. ERCP image shows a normal-caliber cystic duct (solid arrow). Note the undulating contour of the duct produced by the valves of Heister. An air bubble (open arrow) is noted in the common bile duct.
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In most cases, the normal cystic duct is not seen at US. However, with optimal technique, the normal cystic duct can be visualized in up to 50% of cases as an anechoic tubular structure connecting the gallbladder and bile duct (Fig 3). A cystic duct that runs parallel to the distal extrahepatic bile duct may be confused with a vessel; however, differentiation is possible with Doppler US (6).
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Figure 3a. Normal cystic duct anatomy. (a) Oblique US image of the right upper quadrant shows the site of entry of the cystic duct (arrow) into the middle one-third of the extrahepatic bile duct (bd). (b) Sagittal US image of the right upper quadrant demonstrates the cystic duct (curved arrow), gallbladder neck (straight arrow), and body of the gallbladder (g).
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Figure 3b. Normal cystic duct anatomy. (a) Oblique US image of the right upper quadrant shows the site of entry of the cystic duct (arrow) into the middle one-third of the extrahepatic bile duct (bd). (b) Sagittal US image of the right upper quadrant demonstrates the cystic duct (curved arrow), gallbladder neck (straight arrow), and body of the gallbladder (g).
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The cystic duct is not routinely visualized at CT. In some cases, the cystic duct can be traced to its point of insertion into the extrahepatic bile duct (Fig 4). The cystic duct appears as a low-attenuation tubular structure with thin, enhancing walls. The gallbladder neck and cystic duct are often folded or tortuous. When the cystic duct has a long, parallel course relative to the extrahepatic duct, the adjacent ducts seen at cross-sectional imaging are bilobular or septated (7).
MR cholangiopancreatography depicts the cystic duct and biliary tract as high-signal-intensity structures. The cystic duct is routinely seen at MR cholangiopancreatography and can be traced to its junction with the extrahepatic bile duct in most cases (Fig 5). If overlap of the cystic duct and extrahepatic bile duct occurs, a change in the angle of image acquisition allows differentiation of the two structures. In addition, alteration of the angle of image acquisition can result in improved visualization of the cystic duct and clarification of complex or aberrant ductal anatomy (8–11).
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Figure 5. Coronal oblique MR cholangiopancreatogram demonstrates the normal cystic duct (arrow) connecting the gallbladder to the extrahepatic bile duct (arrowhead). Gallbladder calculi are also present.
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As with CT, the cystic duct is not usually visualized at axial MR imaging. T2-weighted sequences that show high-signal-intensity bile in the gallbladder and ductal system are optimal for cystic duct delineation. The cystic duct may also be visualized on T1-weighted images when the cystic duct contains concentrated, high-signal-intensity bile (8–11).
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Anatomic Variants
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Variations in Cystic Duct Insertion
Congenital anatomic variants of the cystic duct are common, occurring in 18%–23% of cases. The cystic duct inserts into the middle one-third of the extrahepatic bile duct in 75% of cases and into the distal one-third in 10%. It most commonly inserts from a right lateral position but may have an anterior or posterior spiral insertion, low lateral insertion with a common sheath enclosing the cystic duct and common bile duct, proximal insertion, or low medial insertion at or near the ampulla of Vater (Figs 6, 7) (3,12–14).
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Figure 6. Anatomic variants in the cystic duct. Drawings illustrate how the cystic duct may insert into the extrahepatic bile duct with a shows right lateral insertion (A), anterior spiral insertion (B), posterior spiral insertion (C), low lateral insertion with a common sheath (D), proximal insertion (E), or low medial insertion (F).
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Figure 7a. (7a) Cholangiogram shows a right lateral insertion of the cystic duct (arrows) into the extrahepatic bile duct. (7b) Cholangiogram shows a medial insertion of the cystic duct (arrows) into the extrahepatic bile duct. (7c) Coronal oblique MR cholangiopancrea-togram shows a low, medially inserting cystic duct (straight arrows) that parallels the bile duct (curved arrow).
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Figure 7b. (7a) Cholangiogram shows a right lateral insertion of the cystic duct (arrows) into the extrahepatic bile duct. (7b) Cholangiogram shows a medial insertion of the cystic duct (arrows) into the extrahepatic bile duct. (7c) Coronal oblique MR cholangiopancrea-togram shows a low, medially inserting cystic duct (straight arrows) that parallels the bile duct (curved arrow).
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Figure 7c. (7a) Cholangiogram shows a right lateral insertion of the cystic duct (arrows) into the extrahepatic bile duct. (7b) Cholangiogram shows a medial insertion of the cystic duct (arrows) into the extrahepatic bile duct. (7c) Coronal oblique MR cholangiopancrea-togram shows a low, medially inserting cystic duct (straight arrows) that parallels the bile duct (curved arrow).
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The level of cystic duct insertion may vary, with an abnormal proximal or distal union accounting for 55% of biliary ductal anatomic variants. The cystic duct may join the right hepatic duct, the left hepatic duct (rarely), or the common hepatic duct high in the porta hepatis (Fig 8). It empties into the proximal common hepatic duct or into the right hepatic duct on 0.3% of cholangiograms (12). The insertion may be low in the intrapancreatic or intraduodenal portion or at the level of the ampulla of Vater. Rarely, the cystic duct inserts directly into the duodenum.
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Figure 8a. Parallel course of the cystic duct. (a) ERCP image obtained in a 57-year-old man shows the long, parallel course of the normal cystic duct (straight arrows). A normal bile duct is also noted (curved arrow). (b) Coronal oblique MR cholangiopancreatogram obtained in a 60-year-old man also demonstrates the normal cystic duct (straight arrows) and bile duct (curved arrow) (cf a). (c) Axial CT scan obtained in a 22-year-old woman shows two low-attenuation foci in the pancreatic head representing a long, parallel cystic duct (short arrow) lying posterior to the intrapancreatic portion of the bile duct (long arrow).
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Figure 8b. Parallel course of the cystic duct. (a) ERCP image obtained in a 57-year-old man shows the long, parallel course of the normal cystic duct (straight arrows). A normal bile duct is also noted (curved arrow). (b) Coronal oblique MR cholangiopancreatogram obtained in a 60-year-old man also demonstrates the normal cystic duct (straight arrows) and bile duct (curved arrow) (cf a). (c) Axial CT scan obtained in a 22-year-old woman shows two low-attenuation foci in the pancreatic head representing a long, parallel cystic duct (short arrow) lying posterior to the intrapancreatic portion of the bile duct (long arrow).
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Figure 8c. Parallel course of the cystic duct. (a) ERCP image obtained in a 57-year-old man shows the long, parallel course of the normal cystic duct (straight arrows). A normal bile duct is also noted (curved arrow). (b) Coronal oblique MR cholangiopancreatogram obtained in a 60-year-old man also demonstrates the normal cystic duct (straight arrows) and bile duct (curved arrow) (cf a). (c) Axial CT scan obtained in a 22-year-old woman shows two low-attenuation foci in the pancreatic head representing a long, parallel cystic duct (short arrow) lying posterior to the intrapancreatic portion of the bile duct (long arrow).
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A cystic duct that parallels the extrahepatic bile duct is seen on approximately 10% of cholangiograms (Fig 8) (3). A long, parallel course implies a common fibrous sheath around the cystic duct and common hepatic duct. This anatomy may be problematic at cholecystectomy. Ligation of the cystic duct too close to the common hepatic duct may result in stricture of the latter. Similarly, mistaking the cystic duct for the bile duct can result in iatrogenic injury such as inadvertent ligation or transection of the extrahepatic bile duct. In addition, an unusually long cystic duct remnant (up to 6 cm in length) may be left after cholecystectomy. An enlarged or long cystic duct remnant may be associated with inflammatory changes and formation of calculi, resulting in postcholecystectomy syndrome, a cause of persistent or recurrent biliary symptoms in affected patients (15–17). A long cystic duct remnant may also prove confusing at cross-sectional imaging, which depicts the parallel cystic duct and common hepatic duct as a septated cystic structure in or near the head of the pancreas (1,2,12–14,18).
Low medial insertion of the cystic duct deserves special attention because this anatomic variant may lead to misdiagnosis on imaging studies and thus affect therapeutic intervention. Low medial insertion of the cystic duct occurs when it joins the extrahepatic bile duct from the medial aspect at or near the ampulla of Vater (Fig 6). A parallel course of the cystic duct with a low medial insertion is seen at cross-sectional imaging (CT, MR imaging, US) as a rounded or elongated, septated cystic structure representing the closely apposed extrahepatic bile duct and cystic duct as they course through the head of the pancreas (Fig 8c).
Superimposition of the cystic duct on the extrahepatic bile duct is commonly seen with this anatomic variant. Cystic duct stones in a low, medially inserting cystic duct that joins the common bile duct at the ampulla may be mistaken for stones in the distal bile duct or may result in bile duct obstruction or gallstone pancreatitis (13,14,19) (Figs 9, 10). Retrograde filling of the low, medially inserting cystic duct at ERCP may mimic the common bile duct or pancreatic duct, particularly if the cystic duct is incompletely filled.
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Figure 9. Low medial insertion of the cystic duct into the ampulla of Vater in an 11-year-old girl with recurrent pancreatitis. ERCP image shows direct filling of the cystic duct (single straight arrow) from an ampullary injection of contrast material. The cystic duct and bile duct (double arrows) join at the ampulla. Stones are identified in the cystic duct (curved arrow), and air is noted in the gallbladder (g). Recurrent pancreatitis in the patient was attributed to this abnormal anatomy.
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Figure 10a. Calculus in a low, medially inserting cystic duct mimicking a distal common bile duct calculus in a 69-year-old man. (a) ERCP image shows a low, medially inserting cystic duct remnant (straight arrows) mimicking the distal bile duct. The calculus (curved arrow) in the cystic duct remnant was initially presumed to lie in the distal bile duct. (b) ERCP image obtained after rotating the patient demonstrates a catheter in the cystic duct remnant (straight arrows) and shows that the calculus (curved arrow) lies in the cystic duct remnant. No calculus is seen in the distal bile duct (arrowheads).
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Figure 10b. Calculus in a low, medially inserting cystic duct mimicking a distal common bile duct calculus in a 69-year-old man. (a) ERCP image shows a low, medially inserting cystic duct remnant (straight arrows) mimicking the distal bile duct. The calculus (curved arrow) in the cystic duct remnant was initially presumed to lie in the distal bile duct. (b) ERCP image obtained after rotating the patient demonstrates a catheter in the cystic duct remnant (straight arrows) and shows that the calculus (curved arrow) lies in the cystic duct remnant. No calculus is seen in the distal bile duct (arrowheads).
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Because the low, medially inserting cystic duct frequently overlies the distal common bile duct, attempts to cannulate the common bile duct at ERCP can result in inadvertent introduction of the injection cannula, stone extraction basket, or extraction balloon into the cystic duct (Fig 11). Injury to the cystic duct may occur. Unsuccessful interventional procedures result if placement of stents or instruments into the cystic duct rather than the common bile duct goes unrecognized. A cystic duct remnant that is associated with a low medial insertion is usually longer than normal, either due to encasement in a common sheath with the extrahepatic bile duct or because the junction is in the intrapancreatic or periampullary area. Extraction of bile duct stones can be more problematic because the extraction attempt will frequently result in the stones slipping back and forth into the cystic duct remnant.
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Figure 11a. Low medial insertion of a dilated cystic duct and biliary obstruction resulting in problematic endoscopic intervention in a 63-year-old woman. (a) Anteroposterior ERCP image shows marked dilatation of the bile duct (bd) secondary to ampullary carcinoma. A guide wire (arrows) inserted for stent placement appears to penetrate the wall of the bile duct. The pancreatic duct (pd) is also noted. (b) ERCP image obtained with the patient in a steep oblique position reveals that the guide wire (arrows) does not enter the bile duct (bd) but is coiled in a low, medially inserting cystic duct that overlapped the bile duct on the anteroposterior view (cf a). Repositioning of the guide wire resulted in satisfactory stent placement in the bile duct rather than in the cystic duct. Stent placement in the cystic duct would have been ineffective in relieving the bile duct obstruction. (c) Later ERCP image obtained following removal of the endoscope shows the low medial insertion of the cystic duct (arrows). The opacified gallbladder (g) is also noted.
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Figure 11b. Low medial insertion of a dilated cystic duct and biliary obstruction resulting in problematic endoscopic intervention in a 63-year-old woman. (a) Anteroposterior ERCP image shows marked dilatation of the bile duct (bd) secondary to ampullary carcinoma. A guide wire (arrows) inserted for stent placement appears to penetrate the wall of the bile duct. The pancreatic duct (pd) is also noted. (b) ERCP image obtained with the patient in a steep oblique position reveals that the guide wire (arrows) does not enter the bile duct (bd) but is coiled in a low, medially inserting cystic duct that overlapped the bile duct on the anteroposterior view (cf a). Repositioning of the guide wire resulted in satisfactory stent placement in the bile duct rather than in the cystic duct. Stent placement in the cystic duct would have been ineffective in relieving the bile duct obstruction. (c) Later ERCP image obtained following removal of the endoscope shows the low medial insertion of the cystic duct (arrows). The opacified gallbladder (g) is also noted.
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Figure 11c. Low medial insertion of a dilated cystic duct and biliary obstruction resulting in problematic endoscopic intervention in a 63-year-old woman. (a) Anteroposterior ERCP image shows marked dilatation of the bile duct (bd) secondary to ampullary carcinoma. A guide wire (arrows) inserted for stent placement appears to penetrate the wall of the bile duct. The pancreatic duct (pd) is also noted. (b) ERCP image obtained with the patient in a steep oblique position reveals that the guide wire (arrows) does not enter the bile duct (bd) but is coiled in a low, medially inserting cystic duct that overlapped the bile duct on the anteroposterior view (cf a). Repositioning of the guide wire resulted in satisfactory stent placement in the bile duct rather than in the cystic duct. Stent placement in the cystic duct would have been ineffective in relieving the bile duct obstruction. (c) Later ERCP image obtained following removal of the endoscope shows the low medial insertion of the cystic duct (arrows). The opacified gallbladder (g) is also noted.
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Anomalous Bile Ducts
Anomalous or aberrant bile ducts are usually of no clinical significance, unless they lead to diagnostic confusion on imaging studies or result in increased potential for iatrogenic injury. Ducts at greatest risk for injury at cholecystectomy are those that course near the cystic duct or gallbladder or empty directly into these structures. Anomalous ducts that empty directly into the cystic duct (cysticohepatic ducts) are found in 1%–2% of individuals (Fig 12a). Accessory bile ducts, especially those arising from the right lobe, may join the common hepatic duct at its junction with the cystic duct or may insert directly into the cystic duct (Fig 12b). Up to 5% of patients will have a major right segmental bile duct joining the extrahepatic bile duct at or near the cystic duct. This anatomic variant creates a risk of inadvertent ligation or transection of the aberrant duct near the cystic duct insertion at cholecystectomy. Rare anomalies of the cystic duct include insertion into the right hepatic duct, double cystic ducts with or without a duplicated gallbladder, and absence of the cystic duct with the gallbladder emptying directly into the common bile duct (13, 14, 18,21–23).
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Figure 12a. Aberrant junction of the bile duct and cystic duct. (a) ERCP image shows an aberrant right hepatic duct (small arrows) entering the cystic duct (large arrow). (b) Coronal MR cholangiopancreatogram obtained in a different patient demonstrates an aberrant right hepatic duct (small arrows) draining a circumscribed portion of the liver and entering the common hepatic duct 4 cm distal to the confluence of the right and left hepatic ducts. The cystic duct (large arrow) drains into the aberrant right hepatic duct. (Figure 12 reprinted, with permission, from reference 20.)
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Figure 12b. Aberrant junction of the bile duct and cystic duct. (a) ERCP image shows an aberrant right hepatic duct (small arrows) entering the cystic duct (large arrow). (b) Coronal MR cholangiopancreatogram obtained in a different patient demonstrates an aberrant right hepatic duct (small arrows) draining a circumscribed portion of the liver and entering the common hepatic duct 4 cm distal to the confluence of the right and left hepatic ducts. The cystic duct (large arrow) drains into the aberrant right hepatic duct. (Figure 12 reprinted, with permission, from reference 20.)
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Pathologic Processes
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Calculous Disease
In 95% of cases, acute cholecystitis is caused by a stone obstructing the cystic duct. Small stones (<3 mm) may pass readily through the cystic duct. However, when calculous obstruction occurs, inflammation and distention of the gallbladder result and may eventually lead to gallbladder ischemia and transmural necrosis if the obstruction persists.
Sometimes, the obstructing calculus and the distended gallbladder may be identified on conventional radiographs (Fig 13a). However, only 15%–20% of gallstones are sufficiently dense to allow detection on conventional radiographs. Although US permits diagnosis of acute cholecystitis with a high degree of confidence (positive predictive value = 92%, negative predictive value = 95%), the obstructing cystic duct stone may be difficult to visualize due to a minimal amount of surrounding bile and because cystic duct stones may be mistaken for bowel gas (Fig 13b) (24–27). Although CT often reveals gallbladder wall thickening and pericholecystic fluid and depicts complications of cholecystitis such as abscess formation and gallbladder perforation, it depicts only 79% of gallbladder stones seen at US and rarely depicts cystic duct stones (24–27).
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Figure 13a. Calculous disease. (a) Conventional anteroposterior radiograph of the abdomen obtained in a 54-year-old man shows a calcified stone in the expected location in the cystic duct (arrow) and demonstrates milk of calcium bile in the gallbladder (arrowheads). (b) Sagittal US image of the gallbladder obtained in the same patient demonstrates a stone impacted in the cystic duct (arrow). Acoustic shadowing is noted posterior to the stone (arrowheads). (c) PTC image obtained in a 31-year-old man reveals multiple cystic duct stones (solid arrows) as well as a stone impacted in the distal bile duct (open arrow). (d) Coronal oblique MR cholangiopancreatogram obtained in a 33-year-old man shows a stone in the cystic duct (arrow). Stones are also present in the gallbladder (g).
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Figure 13b. Calculous disease. (a) Conventional anteroposterior radiograph of the abdomen obtained in a 54-year-old man shows a calcified stone in the expected location in the cystic duct (arrow) and demonstrates milk of calcium bile in the gallbladder (arrowheads). (b) Sagittal US image of the gallbladder obtained in the same patient demonstrates a stone impacted in the cystic duct (arrow). Acoustic shadowing is noted posterior to the stone (arrowheads). (c) PTC image obtained in a 31-year-old man reveals multiple cystic duct stones (solid arrows) as well as a stone impacted in the distal bile duct (open arrow). (d) Coronal oblique MR cholangiopancreatogram obtained in a 33-year-old man shows a stone in the cystic duct (arrow). Stones are also present in the gallbladder (g).
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Figure 13c. Calculous disease. (a) Conventional anteroposterior radiograph of the abdomen obtained in a 54-year-old man shows a calcified stone in the expected location in the cystic duct (arrow) and demonstrates milk of calcium bile in the gallbladder (arrowheads). (b) Sagittal US image of the gallbladder obtained in the same patient demonstrates a stone impacted in the cystic duct (arrow). Acoustic shadowing is noted posterior to the stone (arrowheads). (c) PTC image obtained in a 31-year-old man reveals multiple cystic duct stones (solid arrows) as well as a stone impacted in the distal bile duct (open arrow). (d) Coronal oblique MR cholangiopancreatogram obtained in a 33-year-old man shows a stone in the cystic duct (arrow). Stones are also present in the gallbladder (g).
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Figure 13d. Calculous disease. (a) Conventional anteroposterior radiograph of the abdomen obtained in a 54-year-old man shows a calcified stone in the expected location in the cystic duct (arrow) and demonstrates milk of calcium bile in the gallbladder (arrowheads). (b) Sagittal US image of the gallbladder obtained in the same patient demonstrates a stone impacted in the cystic duct (arrow). Acoustic shadowing is noted posterior to the stone (arrowheads). (c) PTC image obtained in a 31-year-old man reveals multiple cystic duct stones (solid arrows) as well as a stone impacted in the distal bile duct (open arrow). (d) Coronal oblique MR cholangiopancreatogram obtained in a 33-year-old man shows a stone in the cystic duct (arrow). Stones are also present in the gallbladder (g).
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In contrast to US and CT, which provide anatomic information about the gallbladder and cystic duct, cholescintigraphy provides functional information regarding cystic duct patency. Nonvisu-alization of the gallbladder 1 hour following administration of the radionuclide is considered evidence of cystic duct obstruction. Adjuvant use of low-dose intravenous morphine to contract the sphincter of Oddi, which diverts the isotope into the gallbladder if the cystic duct is patent, is helpful in reducing the prevalence of false-positive studies. Cholescintigraphy has a sensitivity of 95% and a specificity of 100% in the diagnosis of acute cholecystitis secondary to cystic duct obstruction (25,26,28,29).
At direct cholangiography, the cystic duct is usually readily opacified. Cystic duct stones are identified as sharply defined filling defects in the contrast material–filled lumen (Fig 13c). Occluding cystic duct stones prevent complete filling of the cystic duct. More recently, MR cholangiopancreatography has been used to examine the gallbladder and cystic duct in the setting of acute cholecystitis. Cystic duct stones may be identified at MR cholangiopancreatography as low-signal-intensity defects surrounded by high-signal-intensity bile (Fig 13d). MR cholangiopancreatography has high sensitivity in detecting cystic duct stones (100% in a preliminary report) (30).
Mirizzi Syndrome
Mirizzi syndrome occurs when a gallstone impacted in the cystic duct results in extrinsic compression and obstruction of the extrahepatic bile duct (Fig 14). For this to occur, the cystic duct usually must run parallel to the extrahepatic bile duct. Preoperative recognition of this condition is therefore important to avoid inadvertent ligation or severance of the bile duct (31,32).
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Figure 14. Mirizzi syndrome in an 85-year-old woman. PTC image demonstrates a large calculus (arrow) impacted in a dilated cystic duct (arrowheads) that parallels and obstructs the common hepatic duct (chd). The gallbladder (g) is opacified.
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The diagnosis of Mirizzi syndrome may be suggested at US or CT when a stone is identified at the junction of the cystic duct and extrahepatic bile duct and is seen in conjunction with dilatation of the bile duct proximal to the stone and a normal-caliber duct distal to the stone (Fig 15) (33,34). ERCP or PTC is often necessary to confirm the diagnosis. MR cholangiopancreatography may provide a noninvasive alternative to ERCP and PTC in the diagnosis of Mirizzi syndrome (Fig 16) (35).
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Figure 15a. Mirizzi syndrome in a 66-year-old man. (a) Axial CT scan of the abdomen shows dilated intrahepatic bile ducts (arrowheads). (b) Axial CT scan of the abdomen shows a 2.2-cm cystic duct stone with a calcified rim (arrow) overlying the location of the extrahepatic bile duct and resulting in biliary dilatation.
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Figure 15b. Mirizzi syndrome in a 66-year-old man. (a) Axial CT scan of the abdomen shows dilated intrahepatic bile ducts (arrowheads). (b) Axial CT scan of the abdomen shows a 2.2-cm cystic duct stone with a calcified rim (arrow) overlying the location of the extrahepatic bile duct and resulting in biliary dilatation.
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Figure 16a. Mirizzi syndrome in a 46-year-old woman. (a) Coronal MR cholangiopancreatogram reveals a 1.2-cm calculus (arrow) resulting in biliary dilatation. Gallbladder calculi are also noted (arrowheads). (b) Coronal MR cholangiopancreatogram obtained 5 mm anterior to a shows two calculi (arrowheads) in the dilated cystic duct, which parallels the extrahepatic bile duct. The inferior calculus corresponds to the ductal calculus seen in a. This calculus eroded through the wall of the cystic duct into the extrahepatic bile duct, bridging the two structures and resulting in compression and obstruction of the common hepatic duct. (c) ERCP image demonstrates a calculus in the cystic duct (arrowhead) as well as the larger, more inferior calculus (arrow) resulting in obstruction of the bile duct (bd). (Figure 16 reprinted, with permission, from reference 35.)
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Figure 16b. Mirizzi syndrome in a 46-year-old woman. (a) Coronal MR cholangiopancreatogram reveals a 1.2-cm calculus (arrow) resulting in biliary dilatation. Gallbladder calculi are also noted (arrowheads). (b) Coronal MR cholangiopancreatogram obtained 5 mm anterior to a shows two calculi (arrowheads) in the dilated cystic duct, which parallels the extrahepatic bile duct. The inferior calculus corresponds to the ductal calculus seen in a. This calculus eroded through the wall of the cystic duct into the extrahepatic bile duct, bridging the two structures and resulting in compression and obstruction of the common hepatic duct. (c) ERCP image demonstrates a calculus in the cystic duct (arrowhead) as well as the larger, more inferior calculus (arrow) resulting in obstruction of the bile duct (bd). (Figure 16 reprinted, with permission, from reference 35.)
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Figure 16c. Mirizzi syndrome in a 46-year-old woman. (a) Coronal MR cholangiopancreatogram reveals a 1.2-cm calculus (arrow) resulting in biliary dilatation. Gallbladder calculi are also noted (arrowheads). (b) Coronal MR cholangiopancreatogram obtained 5 mm anterior to a shows two calculi (arrowheads) in the dilated cystic duct, which parallels the extrahepatic bile duct. The inferior calculus corresponds to the ductal calculus seen in a. This calculus eroded through the wall of the cystic duct into the extrahepatic bile duct, bridging the two structures and resulting in compression and obstruction of the common hepatic duct. (c) ERCP image demonstrates a calculus in the cystic duct (arrowhead) as well as the larger, more inferior calculus (arrow) resulting in obstruction of the bile duct (bd). (Figure 16 reprinted, with permission, from reference 35.)
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Cystic Duct–Duodenal Fistula
Fistulas between the duodenum and cystic duct or gallbladder occur most often due to erosion of an impacted gallstone but may also be seen in association with peptic ulcer disease, neoplasia, and trauma. Eighty percent of enterobiliary fistulas occur between the cystic duct or gallbladder neck and the postapical duodenum immediately beyond the duodenal bulb (36). The gallbladder in cystic duct–duodenal fistula is frequently shrunken, mimicking a pseudodiverticulum of the duodenal bulb (Fig 17). A cystic duct–duodenal fistula may be suggested when pneumobilia is identified on conventional radiographs. Direct cholangiography or an upper gastrointestinal series shows the fistula extending laterally or cephalad from the duodenal bulb. An "impending" cystic duct–duodenal fistula may be identified as a cystic duct stone compressing the duodenum prior to formation of a fistula (Fig 18).
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Figure 17. Cystic duct-duodenal fistula. PTC image demonstrates a fistula (arrow) extending from the cystic duct (arrowheads) to the duodenal bulb (d). Note the shrunken gallbladder (g), which is a common finding in this setting.
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Figure 18a. Impending cystic duct-duodenal fistula in a 62-year-old woman. (a) Axial CT scan of the abdomen shows a large stone with rim calcification in the cystic duct (arrowhead) deforming the contrast material-filled duodenum (d). Note also the shrunken gallbladder (arrow). (b) Image from an upper gastrointestinal series demonstrates the calcified gallstone (arrowheads) compressing and deforming the duodenal bulb (arrows). Upper endoscopy revealed partial erosion of the stone into the duodenum with associated duodenal ulcerations.
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Figure 18b. Impending cystic duct-duodenal fistula in a 62-year-old woman. (a) Axial CT scan of the abdomen shows a large stone with rim calcification in the cystic duct (arrowhead) deforming the contrast material-filled duodenum (d). Note also the shrunken gallbladder (arrow). (b) Image from an upper gastrointestinal series demonstrates the calcified gallstone (arrowheads) compressing and deforming the duodenal bulb (arrows). Upper endoscopy revealed partial erosion of the stone into the duodenum with associated duodenal ulcerations.
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Cystic Duct Changes Related to Biliary Obstruction
When the cystic duct insertion is located above an obstructing bile duct lesion, the cystic duct usually dilates in proportion to common bile duct dilatation. The cystic duct may dilate markedly so that it mimics the gallbladder or a dilated right hepatic branch. However, the cystic duct above an obstructing bile duct lesion does not always dilate as the proximal ducts dilate; it may remain normal in caliber even though the extrahepatic bile duct is markedly dilated. The dilated cystic duct in an obstructed, dilated ductal system usually returns to normal caliber if the ductal system is decompressed, similar to the decrease in caliber of the decompressed intrahepatic or extrahepatic bile ducts (4,19).
The appearance of a dilated, tortuous cystic duct overlying the dilated common bile duct in biliary obstruction can be confusing at direct cholangiography and should be accurately identified to avoid inadvertent cannulation of the cystic duct at PTC or ERCP. Bile leakage, cystic duct injury, or mistaken placement of the proximal end of an endoscopic stent into the cystic duct are recognized complications (3,37).
The dilated cystic duct is readily identified at US, CT, and MR cholangiopancreatography. At CT, the dilated, tortuous cystic duct seen in cross-section on axial images may mimic a multilocu-lated cystic mass in the porta hepatis or in the head of the pancreas. MR cholangiopancreatography demonstrates the dilated cystic duct as a high-signal-intensity ductal structure bridging the gallbladder and extrahepatic bile duct. Prominent valves of Heister may be visualized and recognition of stones made easier if the cystic duct is dilated (4,6,7).
Neoplastic Involvement of the Cystic Duct
The cystic duct may demonstrate direct neoplastic involvement by primary tumor arising in the cystic duct or adjacent gallbladder. Bile duct carcinomas are less common than gallbladder carcinomas; however, if the bile duct carcinoma originates near the cystic duct origin, the cystic duct may be occluded by tumor or directly invaded by the bile duct neoplasm (Fig 19a). Bile duct tumors more commonly involve the proximal bile ducts and are less frequently located in the middle or distal extrahepatic bile duct where the cystic duct usually inserts (4,26). The cystic duct may be invaded or compressed by primary or secondary liver tumors or, less commonly, by adjacent pancreatic head neoplasms (Fig 19b). Regardless of its origin, a tumor affecting the cystic duct is usually visible at CT, US, or MR imaging.
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Figure 19a. Neoplastic involvement of the cystic duct. (a) ERCP image obtained in a 57-year-old woman demonstrates irregular narrowing of the cystic duct (white arrows), which is involved by cholangiocarcinoma. A high-grade stricture of the common hepatic duct produced by the tumor is also noted (black arrow). (b) PTC image obtained in a 60-year-old woman shows narrowing of the cystic duct (straight arrows) and encasement of the adjacent extrahepatic bile duct (curved arrow) by carcinoma arising from the superior aspect of the pancreatic head.
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Figure 19b. Neoplastic involvement of the cystic duct. (a) ERCP image obtained in a 57-year-old woman demonstrates irregular narrowing of the cystic duct (white arrows), which is involved by cholangiocarcinoma. A high-grade stricture of the common hepatic duct produced by the tumor is also noted (black arrow). (b) PTC image obtained in a 60-year-old woman shows narrowing of the cystic duct (straight arrows) and encasement of the adjacent extrahepatic bile duct (curved arrow) by carcinoma arising from the superior aspect of the pancreatic head.
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Cystic Duct Involvement by Primary Sclerosing Cholangitis
Primary sclerosing cholangitis is an uncommon disease of unknown cause characterized by inflammation and fibrosis of the biliary tract. Diffuse, multifocal strictures involving both intrahepatic and extrahepatic bile ducts are the most common finding in primary sclerosing cholangitis. The cystic duct may also be involved by primary sclerosing cholangitis. MacCarty et al (38) noted that in 60 of 86 patients with primary sclerosing cholangitis in whom the cystic duct was visualized at direct cholangiography, 18% (n = 11) had cystic duct involvement. Cystic duct abnormalities included strictures, mural irregularities, and diverticula similar to the changes seen in the intrahepatic and extrahepatic bile ducts (Fig 20).The detection of cystic duct involvement by primary sclerosing cholangitis may be difficult due to the normal valves of Heister, which may obscure the findings. In addition, underfilling of the cystic duct can result in an appearance of the cystic duct that simulates primary sclerosing cholangitis.
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Figure 20. Involvement of the cystic duct by primary sclerosing cholangitis in a 34-year-old man. ERCP image shows mural irregularity of the cystic duct (arrows) due to primary sclerosing cholangitis. The intrahepatic and extrahepatic bile ducts show similar changes associated with this disease entity.
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Postsurgical Alterations and Abnormalities
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Normal Postsurgical Findings
After cholecystectomy, a variable length of the cystic duct is left as a remnant. Surgical cholangiography is performed with needle cannulation of the remnant to exclude retained stones. The remnant is readily seen at direct cholangiography (Fig 21) and may be seen at MR cholangiopancreatography but is more difficult to see at CT and US. Usually, a cystic duct remnant of 1–2 cm is left at surgery, although remnants up to 6 cm in length may be seen. A longer remnant may be left after cholecystectomy when a long, parallel cystic duct or low medial insertion is present. Approximately 10% of repeat surgeries performed after cholecystectomy are attributable to complications associated with the cystic duct remnant (eg, postoperative bile leakage, stricture, fistula formation). Retained stones in the cystic duct remnant, "amputation neuromas," and suture granulomas of the cystic duct remnant may cause recurrent pain. A rare postoperative complication is a cystic duct mucocele in which the remnant becomes distended with mucus. Biliary obstruction may occur if the mucocele impinges on the bile duct (15–17,39,40).
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Figure 21. Normal cystic duct remnant in a 61-year-old man. Intraoperative cholangiogram shows a normal cystic duct remnant (arrow). The injection cannula is seen entering the remnant.
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A primary duct-to-duct anastomosis (choledochocholedochostomy) or a biliary-enteric anastomosis may be created in liver transplant recipients. Regardless of the type of anastomosis, the gallbladder is removed from both the donor and the recipient prior to transplantation. Two cystic duct remnants (one each in the donor and recipient duct) may be seen with a primary duct-to-duct anastomosis (Fig 22) (40–42). The cystic duct remnant or remnants can be visualized at direct cholangiography or MR cholangiopancreatography. Overlap of the cystic duct remnant with the anastomosis makes evaluation for anastomotic stricture more difficult. With a choledochoenteric anastomosis, the ductal anastomosis is usually connected to the common hepatic duct, and no cystic duct remnant remains.
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Figure 22. Normal donor and recipient cystic duct remnants following liver transplantation in a 26-year-old man. T tube cholangiogram demonstrates two cystic duct remnants, one arising from the donor bile duct (arrow) and the other arising from the recipient bile duct (arrowheads).
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A T tube or a straight tube (Turcotte tube) is used for stent placement in a duct-to-duct anastomosis and to provide easy access for cholangiography. A T tube stent is placed through an opening made at choledochotomy into the common bile duct of the recipient. When a straight tube is used, placement is via the donor cystic duct remnant, thus obviating choledochotomy. When a straight tube is removed, leakage from the donor cystic duct remnant occurs in up to 5% of patients (40–42).
Abnormal Postsurgical Findings
The most common problem associated with the cystic duct remnant is retained calculi. Retained bile duct stones occur in up to 5% of patients undergoing cholecystectomy. Fewer than 1% of retained stones are located in the cystic duct remnant (4,15–17,39) and can be identified at surgical cholangiography or postoperative cholangiography (Fig 23). Cystic duct remnant stones may be blocked in the cystic duct by an indwelling T tube. If the retained stones are located in a cystic duct overlying the bile duct, the stones may be mistakenly identified as bile duct stones. Dislodgement of stones from the cystic duct remnant may be difficult at endoscopic or percutaneous extraction owing to the tortuosity of the cystic duct, the acute angle of junction with the common bile duct, or the short length of the cystic duct remnant preventing successful placement of an extraction basket or balloon (3).
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Figure 23. Retained stone in a cystic duct remnant in a 35-year-old woman who had undergone cholecystectomy 10 days earlier. T tube cholangiogram shows a stone in the cystic duct remnant (arrow).
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Cystic duct leakage may occur after cholecystectomy. These leaks are usually small and occur early in the postoperative period or after removal of tubes that were surgically placed via the cystic duct remnant (4,15–17,42,43). Radionuclide he-patobiliary imaging can be used to verify cystic duct leakage, although direct cholangiography is required to show the precise anatomic site of the leak (Fig 24). These studies demonstrate leakage from the cystic duct into the gallbladder fossa and subhepatic space. Treatment with a transampullary endoscopically-placed stent is generally successful in sealing the leak, and surgical repair is not usually required.
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Abstract
LEARNING OBJECTIVES FOR TEST...
