Technique

Communication between the gastroenterologist and radiologist is critical, for both patient care and medical-legal reasons. With both services usually on busy schedules and frequently being physically separated, the radiologist can obtain information through the dedicated imaging technologist associated with the examination, closed-circuit television, and the gastroenterologist’s dictation from the electronic medical record system.

The examination should begin with an image centered over the patient’s right upper quadrant even before the patient is endoscoped. This image will allow the gastrointestinal service to appreciate any radiopaque material that might obscure ERCP imaging. This image will also display any calcifications related to the pancreatic and biliary systems that might be covered up with the injected 150 to 300 mg iodine/mL concentration of contrast medium that is typically used to opacify either system. This image and subsequent images are best obtained at 90 to 100 kVp, depending on the patient’s size. However, the fluoroscopic and imaging techniques are frequently adjusted automatically by the fluoroscopic unit.

The duct system is ideally imaged with the cannula placed initially at the level of the sphincter. However, the gastroenterologist will frequently feel more comfortable with the cannula advanced into the duct system for better purchase. Relatively slow injection rate with sequential imaging documentation is most useful for the interpreting radiologist. For example, biliary tract stones tend to congregate distally. A deep cannulation and rapid injection of contrast material can make display of these filling defects difficult.

The patient is typically placed in the prone oblique position for this examination. This results in flowing of the relatively heavier contrast agent away from the cannula, coursing “upstream.” With the injection, admixture artifacts may develop both at the cannula tip and at the site of inflow from the cystic duct into the biliary tract.

Also, because of the patient’s prone position, the left hepatic duct system will fill before the right. If the right duct system fills first, as is usual for T-tube cholangiography, in which the patient is typically supine, careful examination for left-sided obstruction is needed. A normal cystic duct and gallbladder should be filled during this examination. Images of early filling of the gallbladder may demonstrate the relatively heavy contrast agent’s beginning to outline the dependent gallstones in the gallbladder if it is present.

Imaging in multiple projections can be helpful in laying out normal or any abnormal anatomy. An attempt should be made to identify all of the central intrahepatic bile ducts. Lateral positioning of the patient can be helpful in distinguishing right from left ducts. In this position, the more anterior ducts belong to the left system ( Fig. 74-1 ).

Schematic of the biliary tract.

A view from the lateral projection, with the patient prone, demonstrates that the left intrahepatic biliary tract ( light gray ) will fill before the right intrahepatic duct system ( dark gray ). Also in the prone position, injected contrast medium will flow away from the sphincteric segment because of the gentle downward course of the extrahepatic biliary tract.

Finally, delayed images can be helpful. Allowing some of the contrast agent to flow out of the duct system, greatly facilitated by supine positioning, can bring out findings lost in the dense contrast. Delayed imaging can also help confirm obstruction even if the ducts themselves do not appear to be dilated. A normal pancreatic duct should be drained of contrast material within 10 minutes from injection; the biliary tract, without a gallbladder, should take no more than 45 minutes.

Anatomy

Biliary Tract

The biliary tract can be divided into the intrahepatic and extrahepatic systems. The intrahepatic biliary tract follows the arterial blood supply of the liver draining the eight hepatic segments. There is, however, moderate variability in the intrahepatic duct network; for example, the duct draining the right posterior segment is frequently aberrant ( Fig. 74-2 ). The intrahepatic ducts should appear smooth and gently taper as they course peripherally. The angles formed by these branches should be acute. Changes resulting in pruning of peripheral ducts, stiffening of the duct system, or deviation of the “flowing” appearance of this duct network should raise concern.

Bile duct aberrancy.

The duct serving the right posterior hepatic segment is the most common anomalous intrahepatic biliary tree duct segment. A post–liver transplantation T-tube cholangiogram shows the right posterior duct ( straight arrow ) exiting below the bifurcation ( arrowhead ), in this case consisting of the right anterior segment and the left hepatic duct. Also note that the transplant’s cystic duct ( curved arrow ) originates from this aberrant duct.

The extrahepatic ductal system actually begins with the right and left hepatic ducts, both of which have components outside the liver. The union of these two duct segments forms the common hepatic duct (CHD), which is approximately 2 to 4 cm in length.

The cystic duct joins the CHD at an acute angle, typically on the CHD’s right side. The cystic duct insertion may be anomalous. It may insert abnormally upstream in the CHD or even into the right posterior intrahepatic duct (see Fig. 74-2 ). It may also join the extrahepatic duct very distally or medially ( Fig. 74-3 ). This variant anatomy can lead to anatomic confusion and possible surgical mishap, or it may predispose to the development of complications, such as the Mirizzi syndrome.

Aberrant cystic duct.

A magnified view of the distal common duct shows the cystic duct ( arrow ) originating medially from the intrapancreatic portion of the extrahepatic biliary tree. This anatomy is important to identify, alerting the surgeon before possible laparoscopic cholecystectomy. Numerous faceted gallstones are present in both the cystic and common ducts.

The common bile duct (CBD) is formed with the union of the cystic duct and CHD. This 10-cm duct segment courses caudally and gently anteriorly when the patient is in the usual prone position during the ERCP examination (see Fig. 74-1 ). The combined CHD and CBD segments may be referred to as the common duct or extrahepatic biliary tree.

The distal CBD courses into the duodenal wall and into the major duodenal papilla, also named the papilla of Vater. This distal segment is usually smooth, but it may appear finely pleated or may contain a small diverticulum.

The distal CBD is usually met distally by the main pancreatic duct (MPD), the union of which forms a common channel, also known as the ampulla of Vater, of variable length ( Fig. 74-4A ). In approximately 10% to 20% of cases, each duct system enters the papilla and drains into the duodenum separately. This common channel varies in length from 2 to 15 mm but averages 5 mm.

Sphincter segment anatomy.

A. A schematic demonstrates the three types of duct unions: the Y type, with a relatively long common channel; a short common channel, leading to a V appearance; and, in a minority of cases, the two ducts enter the papilla separately in a U appearance. CBD , Common bile duct; PD , pancreatic duct. B. An abnormally long and ectatic channel is seen in this ERCP image. The sphincter is contracted ( arrowhead ), but the common channel ( arrow ) extends beyond the muscle wrap, allowing direct communication of the two duct systems. This is thought to be the anatomic origin of choledochal cyst development.

These two ductal systems are wrapped in smooth muscle called the sphincter of Oddi ( Fig. 74-4B ), measuring 5 to 15 mm in length. This muscle segment has a constant, tonic basal pressure on which interval phasic contractions of approximately two or three times per minute are superimposed. These contractions can be appreciated at fluoroscopy during injection of contrast material. This phasic contraction can squeeze the ductal segments together to create the convex-upward appearance of a stone. This so-called pseudocalculus sign is reversed with the contraction’s end ( Fig. 74-5 ).

The pseudocalculus appearance.

A. The initial ERCP image is obtained with the sphincter contracted, causing the appearance of an impacted stone. B. Seconds later, the sphincter relaxes, showing the normal, patent duct systems.

The diameter of the biliary tract should be measured at the CBD. Most authors suggest a maximal diameter, corrected for magnification with the known 12-mm-diameter of the therapeutic endoscope, to be less than 12 mm. With age, presumably related to degeneration of the duct’s elastic fiber network, the CBD may increase in diameter, resulting in a “floppy duct.” The normal CBD diameter of ERCP imaging will be greater than that of ultrasound, CT, and MRI, most likely related to the combination of active injection of contrast material and duct relaxation produced by conscious sedation used at ERCP.

Pancreatic Duct

The length of the MPD varies from 10 to 25 cm, but it averages 16 to 17 cm. It typically has an S-shaped configuration ( Fig. 74-6 ). The “toe” of the S courses horizontally from the sphincter, then ascends cranially. This segment drains the pancreatic head. The MPD then again turns into a horizontal direction corresponding to the “shoulder,” running anterior to the superior mesenteric artery and its vein. The transition from the ascending to the horizontal segment is designated the neck. The remainder of the pancreas is divided between the body and the tail, either with the left side of the spine being the transition point or by simply dividing the duct from the neck to the end of the tail in half.

Normal ERCP appearance.

The main pancreatic duct has an S-shaped appearance, gently tapering as it courses from the head to the tail. In this particular patient, the normal side branches are homogeneously gracile in appearance.

The neck of the MPD may have a subtle, circumferential narrowing without upstream dilation. This normal variant is thought to represent the union of the embryonic dorsal and ventral ducts. Toward the upstream segment of the MPD, there is often bifurcation of the duct as it nears its termination. Anatomically, the tail is proximal and the head is considered distal, although some use upstream to describe anatomy toward the tail and downstream to refer to the anatomy coursing toward the pancreatic head.

The MPD results from the union of the embryologic ventral duct, Wirsung, and the dorsal duct, Santorini. The MPD has a smooth, gentle narrowing from the head to the tail. The maximum diameter, again magnification corrected, at the head is less than 6 mm. The ERCP normal values will again be less than those related to ultrasound, CT, and MRI. With age, the MPD may normally develop a more “stiff” appearance with some subtle ductal irregularity.

There is no “normal” side branch appearance on ERCP. Side branches may have a fine, slender appearance ( Fig. 74-6 ), or they may be wider in diameter. However, a given patient’s side branches should be uniform in appearance and should have a smooth, gentle tapering configuration as they head into the pancreatic parenchyma. Display of the side branch system, as well as of the MPD, to assess for various abnormalities is infrequent in today’s practice with the other imaging methods now available and because the risk of producing pancreatitis is relatively great with MPD injection.

Biliary Tract Neoplasia

Malignant neoplasms involving the biliary tract, both intrahepatic and extrahepatic, usually are manifested as stricture disease and less commonly as filling defects. The strictured biliary tract segment can be the result of direct mural involvement by the tumor or of compression or infiltration from adjacent diseased lymph nodes or hepatic parenchymal tumor. Unfortunately, benign disease involving the biliary tract also frequently results in a strictured appearance ( Box 74-1 ). The different causes of the biliary stricture must be differentiated for appropriate management.

Morphologic appearance can be of some help in this differentiation. Malignant strictures tend to be long (≥1.5 cm), have an irregular, eccentric mural surface, and have a short (<1 cm) transitional zone with a nodular or shouldered appearance. The addition of contrast-enhanced MDCT or MRI can add criteria for a malignant appearance with increasing mural thickness, irregularity of the external mural border, and mural enhancement.

The cholangiographic appearance in identifying a malignant stricture is only approximately 70% to 85% for sensitivity, specificity, positive predictive value, and accuracy, so the added benefit of tissue sampling at ERCP can be important. Cells and tissue can be acquired by various methods: aspirated bile for cytology, brush cytology, fine-needle aspiration of the stricture for cytology, endobiliary forceps biopsy, and even analysis of material clinging to a retrieved plastic stent. Multiple types of acquisition methods will increase return. The sensitivity of either brush cytology or biopsy is approximately 56%, but their combined use improves the return to 73%. It has now been reported that the previous practice of sampling after stricture dilation does not increase the return on sampling. These results can be compared with the use of fine-needle aspiration at endoscopic ultrasound (EUS), which has a high return, at least 80%, for distal malignant strictures from pancreatic cancer or cholangiocarcinoma.

Endoscopic techniques are also useful for stent placement in lower duct malignant strictures. The clinical views of what type of stent to use and when to use stents in malignant strictures are continuing to evolve.

Pancreatic cancer is the most common cause of malignant biliary tract obstruction. Cholangiocarcinoma and gallbladder cancer are the most common primary bile duct tumors. A group of four different types of tumors, including pancreatic cancer and distal cholangiocarcinoma, can occur at the ampullary site to also cause bile duct obstruction, called periampullary tumors. Metastatic disease also is a common cause of malignant biliary tract obstruction, with gastrointestinal tract tumors, hepatocellular carcinoma, and lymphoma being common causes.

Pancreatic cancer involvement of the biliary tract is usually seen in the distal CBD segment, the intrapancreatic portion of the CBD ( Fig. 74-7A, B ). The length of bile duct stricture depends on both the tumor size within the pancreatic head and the nearness of the bile duct to the tumor’s center. The transition of the strictured segment is usually rapid, with a nodular or shouldered appearance. However, as discussed before, pancreatic carcinoma can involve the proximal extrahepatic biliary tree from adjacent peribiliary lymph node involvement, and it can also involve the intrahepatic ducts if there is hepatic metastatic disease ( Fig. 74-7C, D ).

Biliary tract strictures from pancreatic carcinoma.

A. The pancreatic cancer causes a rapid transition to a tight stricture in the intrapancreatic portion of the bile duct with marked upstream dilation. B. In this case, the pancreatic cancer has a longer bile duct stricture that is irregular in appearance ( arrow ). There is also a long diffuse narrowing of the pancreatic cancer in the adjacent main pancreatic duct ( arrowhead ). There is dilation of the upstream main pancreatic duct. There is also nodular effacement of the gas-filled duodenum from the pancreatic cancer. C. In a different patient, the proximal extrahepatic biliary tree ( arrows ) and intrahepatic bile ducts ( arrowheads ) are narrowed by metastatic disease to hilar lymph nodes and hepatic metastatic disease, respectively. D. The corresponding CT section demonstrates the pancreatic tail primary (T), metastatic hilar lymph nodes ( arrow ), and hepatic metastases ( asterisks ).

Cholangiocarcinoma can be intrahepatic or extrahepatic in location. It is classified into one of three types: mass forming, periductal infiltrating, and intraductal growth. The mass-forming type of cholangiocarcinoma arises from small intrahepatic ducts. The carcinoma forms a hepatic parenchymal mass; MDCT and MRI are the most appropriate modalities for its detection and assessment for extent of disease. Cholangiography does not play a significant role in imaging.

The tumor associated with the periductal infiltrating cholangiocarcinoma grows within the wall of the biliary tract, causing mural thickening with an irregular ( Fig. 74-8A ) or smooth ( Fig. 74-8B ) stricture. It spreads in a submucosal manner and tends to infiltrate the periductal anatomy. This tumor frequently begins in the hilar region, where it is referred to as a Klatskin tumor. The tumor can grow upstream or downstream. Unfortunately, it also tends to extend into the periductal and perineural tissues as well as into the lymphatics, where MDCT or MRI may better define the extramural disease. ERCP does have a place if resection is anticipated ( Fig. 74-8C ). Cholangiography can be used to better define the biliary tract anatomy involvement by the Bismuth classification ( Fig. 74-9 ). The Bismuth classification is used to evaluate proximal biliary tract resection of strictures or obstructions of various causes. ERCP can provide important information about the local anatomy through its exquisite spatial display of the duct system.

Cholangiocarcinoma appearances at ERCP.

A. This periductal infiltrating cholangiocarcinoma demonstrates marked mural irregularity and stricturing of the common hepatic duct leading into the hilum. B. Another appearance of the periductal infiltrating cholangiocarcinoma demonstrates a long, smooth stricture. C. This intraductal growing type of cholangiocarcinoma has both a papillary component ( thick arrow ) and also a moderate amount of mural irregularity and narrowing compatible with superficial spread ( arrowheads ). There is also involvement at the bifurcation and intrahepatic ducts ( thin arrows ), which did not allow curative surgery.

Schematic of the Bismuth classification.

A type I configuration represents occurrence of the stricture 2 cm or more from the common hepatic duct bifurcation. A type II configuration has less than 2 cm of normal duct before the bifurcation. The type III configuration leaves only the bifurcation intact. Type IV has narrowing of the bifurcation. Type V refers to injury of aberrant branches of the biliary tree.

(From Taylor AJ, Bohorfoush AG III: Interpretation of ERCP. Philadelphia, Lippincott-Raven, 1997.)

At ERCP, the early periductal infiltrating type of cholangiocarcinoma can be manifested as a relatively short, smooth appearance to simulate a benign stricture. However, because cholangiocarcinoma is usually appreciated later in the disease process, this stricture tends to be longer and more irregular in appearance.

The much less common type of cholangiocarcinoma, the intraductal growing type (also referred to as papillary cholangiocarcinoma), is the most likely type of cholangiocarcinoma to be manifested relatively early in its course. It tends to spread superficially and not invade the bile duct wall. It has a better prognosis compared with the other types of cholangiocarcinoma. At ERCP, this tumor may be a well-defined, smooth, intraluminal papillary protrusion (see Fig. 74-8C ); but there can be multiple papillary projections, and some of these papillary projections may have an irregular surface. The intraductal growing type of cholangiocarcinoma may cause obstruction of the upstream ductal system without clear definition of the tumor itself. This type of cholangiocarcinoma can also produce mucin to cause biliary dilation. There is a complex relationship between the intraductal growing type of cholangiocarcinoma, biliary papilloma or papillomatosis ( Fig. 74-10 ), and intraductal papillary mucinous neoplasm of the bile duct ( Fig. 74-11 ), all of which can be seen as a papillary projection on cholangiography.

Biliary papillomatosis.

The multiple papillary projections protruding into the extrahepatic biliary tree are compatible with papillomatosis.

Intraductal papillary mucinous neoplasm of the biliary tract.

A. Initial injection demonstrates an irregular filling defect in the common hepatic duct. This was a jellylike material with strands of contrast medium visualized in its interstices. B. After removal of this viscid material with a retrieval balloon, the left hepatic ducts and the common hepatic duct are now widely patent. There was no papillary tumor visualized.

Gallbladder carcinoma is the other primary biliary tract malignant neoplasm. Local disease from this primary may spread to the mid or proximal extrahepatic biliary tree by direct extension along the cystic duct, by lymphatics, or by enlarged peribiliary lymph nodes. The stricture may extend to the hilar bifurcation or into the right or left hepatic duct system. The intrahepatic ducts may also be compromised by the cancer’s predilection to invade the adjacent hepatic parenchyma or from metastatic deposits within the liver, which can displace, infiltrate, or obstruct the intrahepatic duct system.

At ERCP, the cystic duct may not fill or only partially fill. The mid to proximal duct can be splayed, be diffusely narrowed, or demonstrate an irregular stricture ( Fig. 74-12 ). Some mass effect, stricture, or obstruction can also be related to enlarged hepatobiliary lymph nodes.

Gallbladder carcinoma.

A. In this case, the gallbladder carcinoma produces an irregular mass effect on the common hepatic duct compatible with invasion ( arrow ). The cystic duct fills only minimally. A right intrahepatic duct ( arrowhead ) is splayed and narrowed by the intrahepatic involvement of the gallbladder cancer. B. The gallbladder cancer in this case displaces the proximal and mid extrahepatic biliary tree from right to left, but there is no significant narrowing. The cystic duct did not fill during this examination. C. A long, moderately severe, smooth narrowing with mild bowing of the common hepatic duct is present in this gallbladder cancer patient. A small segment of the cystic duct does fill in this case.

Distal CBD obstruction, and potentially downstream MPD obstruction, can be caused by a variety of tumors that can occur at the papilla of Vater. Because of the difficulty in imaging, endoscopy, surgery, and even histology to separate these tumors, these tumors are combined under the heading of periampullary tumors. These tumors can be either benign or malignant. Benign tumors in this area are less common and include the ampullary adenoma, local geographic benign tumors, and carcinoid.

Periampullary cancer refer to cancers from one of four structures: the pancreatic head, distal bile duct, duodenum, and ampulla. There are other, rare malignant neoplasms that can occur here as well, such as metastatic disease and lymphoma. Even though these cancers share a similar location and clinical presentation, the underlying histologic type can dictate prognosis. The ampullary and duodenal cancers have the best prognosis, whereas the distal bile duct and pancreatic cancers have the worst.

Although some authors suggest that contrast-enhanced MDCT with three-dimensional reconstruction is the preoperative imaging examination of choice for the periampullary tumor, CT can have difficulty in both the visualization and the accurate assessment of local disease. Biliary or pancreatic duct dilation may be visualized but the underlying tumor not appreciated.

ERCP can be of great help by directly visualizing the periampullary tumor at the time of endoscopy and display the possible intraductal involvement of the tumor during ductal injection of contrast material ( Fig. 74-13 ). Tissue retrieval can also be obtained as well as stenting, if necessary, and even local endoscopic resection in the appropriate case. However, EUS and even transpapillary intraductal ultrasound are frequently used by endoscopists for better assessment of local tissue involvement and possible local lymph node spread. EUS can also be used for fine-needle aspiration of the tumor for histologic diagnosis. A periampullary tumor may not have an intraluminal component. The cholangiogram or pancreatogram may demonstrate only a narrowing without an intraluminal mass. In these cases, tissue retrieval is critical.

Periampullary tumors.

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