Computed tomography imaging has a much higher sensitivity for detecting biliary malignancy than trans-abdominal ultrasound (US) (69% vs. 47%), especially for hilar lesions . The development of multi-detector helical scanners, used in conjunction with rapid injection of contrast media, has markedly improved the resolution of CT scans, providing additional information about etiology, based on the rate of contrast uptake and clearance by focal lesions. Ductal infiltrating cholangicarcinoma commonly presents as a biliary stricture without a discreet mass. It appears as a hypo-attenuating lesion during the arterial phase, with enhancement during the delayed phase (this vascular filling pattern is characteristic of desmoplastic reaction seen in bile duct tumors) [23, 24]. The overall sensitivity of CT scan for detection of cholangiocarcinoma ranges from 40–63% but recent studies have suggested a sensitivity of up to 100% in detecting hilar malignancies during the arterial phase [25–27]. However, multi-detector CT (MDCT) cannot reliably differentiate malignant from benign strictures. Studies have shown a sensitivity of 75–80% and specificity of 60–80% for predicting the nature of biliary strictures using CT imaging [28, 29]. An additional advantage of CT scanning is that it provides information about local spread, nodal and vascular involvement, as well as distant metastasis . MDCT can help identify vascular infiltration that determines resectability. Retrospective studies have reported sensitivity and specificity of 86% and 97%, respectively, for detecting arterial invasion and 85% and 97%, respectively, for portal vein involvement. MDCT has 53% sensitivity and 95% specificity for pre-operative determination of regional lymph node involvement . Even though it is not diagnostic of malignancy in many patients with biliary strictures, CT scanning can help in planning further diagnostic evaluation and management.
Intraductal ultrasonography involves the insertion into the bile duct of a high-frequency ultrasound probe guided by a wire. It provides high-resolution images of the ductal wall and periductal tissues . Multiple studies have shown a sensitivity and diagnostic accuracy of around 80% and 90%, respectively, for IDUS while evaluating biliary strictures without an associated mass lesion [82–84]. In terms of differentiating malignant from benign strictures, a combination of ERCP and IDUS improved the diagnostic accuracy over that of either ERCP or MRCP alone (88% vs. 76% and 58%, respectively) . Meister et al. retrospectively reviewed 397 patients with indeterminate biliary strictures who underwent ERCP with IDUS and found IDUS to have sensitivity, specificity and accuracy of 97.6%, 98% and 92%, respectively . Additionally, IDUS can also help in local T and N staging of tumors with accuracies of 84%, 73%, 71% and 68% for T1, T2, T3 and N1 staging, respectively, but it usually underestimates N staging due to the limited penetration of high-frequency ultrasonic waves. Amongst the various characteristics of benign strictures, a bile duct wall thickness of less than 7 mm and the absence of external compression have a negative predictive value of 100% for excluding malignancy in patients with biliary obstruction without a mass, when seen on cross-sectional imaging . Other features suggestive of malignancy, that are identifiable during IDUS examination, include eccentric wall thickening, disruption of the three-layer wall pattern, hypoechoic mass, invasion of surrounding tissue, the presence of lymph nodes and vascular invasion [88–91]. IDUS is potentially an important adjunct in the evaluation of biliary strictures, especially indeterminate strictures, but it has not been widely used because most ERCP practitioners are not trained in EUS and do not feel comfortable interpreting these images. In patients in whom determination of the etiology of the stricture is not possible despite exhaustive evaluation, a repeat ERCP with IDUS examination, performed by an expert endosonographer trained in both ERCP and IDUS, may help identify patients with low likelihood of malignancy, in whom conservative non-surgical management may be reasonable and separate them from patients with high likelihood of malignancy, in whom surgical exploration may be in order.
Confocal laser endomicroscopy uses an intravenously injected contrast agent and can provide tissue details at microscopic level in real time, using either a catheter probe that can pass through the working channel of the endoscope (pCLE) or a thin probe advanced through the FNA needle (nCLE). The pCLE catheter can be advanced into the biliary system and can provide visualization of epithelial and subepithelial structures and analyses of capillary blood flow, as well as contrast uptake. The most commonly used contrast agent is fluorescein. The pCLE probe can be passed through various ERCP catheters or the working channel of a cholangioscope. The sensitivity for detecting biliary malignancy ranges from 73–83% but it has low specificity, ranging from 33–50% [63, 96, 97]. A standardized classification system, known as the Miami Classification, was proposed to characterize pCLE findings for biliary strictures. The presence of thick white bands (>20 μm), thick dark bands (>40 μm), dark clumps, epithelial structures and contrast leakage were evaluated as factors that could differentiate malignant from benign strictures . This classification was shown to have a fair-to-poor inter-observer agreement when evaluated by six experienced endoscopists . The low specificity (high false positive numbers) is believed to be secondary to changes associated with chronic inflammation and prior biliary manipulation (stenting, brushing, biopsies); hence a new classification system, called the Paris Classification, was recently described . This includes evaluation of additional features such as vascular congestion, dark glandular patterns, increased interglandular space and thickened reticular structures. More prospective data and validation of a standardized classification system is needed before pCLE can be widely accepted as a useful tool in the diagnostic work-up of biliary strictures.
Endoscopic ultrasound is increasingly being used in the diagnostic evaluation of patients with biliary obstruction. It has become the imaging test of choice in patients with distal biliary obstruction, having high sensitivity and accuracy for malignant etiology. The use of EUS-guided fine needle aspiration (EUS-FNA) for the diagnosis of hilar strictures was first proposed in 2000 in a feasibility study of 10 patients with biliary strictures and negative brush cytology . Multiple studies have reported a sensitivity ranging from 40–90%, with most of these showing a sensitivity of more than 70% [64–70]. It is important to note that the majority of these studies included patients with non-conclusive biliary cytology on ERCP .
The exact incidence of biliary strictures is not known and estimates are available only for post-cholecystectomy strictures related to bile duct injuries. Although biliary strictures are usually noted on ERCP or magnetic resonance cholangio-pancreatography (MRCP) in patients with obstructive jaundice, they are sometimes observed in non-jaundiced patients with or without liver chemistry abnormalities. All bile duct strictures in patients with obstructive jaundice should be considered malignant unless a benign etiology is definitively identifiable. The significance of biliary strictures without jaundice is less certain and a much lower proportion of these are malignant. The most common causes of benign biliary strictures include iatrogenic (post liver transplant or cholecystectomy), chronic pancreatitis, primary sclerosing cholangitis, autoimmune diseases (pancreatitis or cholangitis), Mirizzi syndrome and ischemic cholangiopathy ( Table 1 ). Malignant bile duct strictures are usually due to pancreatic adenocarcinoma and cholangiocarcinoma and are less commonly caused by metastatic cancer of the pancreas or liver, ampullary tumors growing into the bile duct, gall bladder cancer obstructing the bile duct or malignant periportal lymph nodes. Pancreatic adenocarcinoma is the most important consideration in patients with distal common bile duct (CBD) strictures. It may present with identifiable mass lesion but in our clinical practice, in about half of patients with pancreatic cancer, a mass lesion is not identifiable by computed tomography (CT) scan or magnetic resonance imaging (MRI) [1, 7]. A mass lesion is usually identifiable by endoscopic ultrasound (EUS) examination in these patients, although a cytological diagnosis of malignancy may be elusive in some cases. Cholangiocarcinoma is the major consideration in patients with stricture of the mid- and proximal extra-hepatic part of the bile duct; hence the main focus in patients with indeterminate bile duct strictures is to rule out an underlying cholangiocarcinoma. The clinical approach to the patient with indeterminate stricture must include a thorough history and physical examination. Particular attention must be paid to the ‘warning signs’ that suggest malignancy, including weight loss, abdominal or back pain, worsening performance status or history of recent surgeries (particularly in the past year).
Multidetector computed tomography findings
Using univariate analysis, we found a number of significant differences between malignant and benign CBD strictures, namely, the margins, presence of invasion into the surrounding tissue, the length, enhancement pattern, and dilatation of the duct proximal to the stricture. In this study, a malignant CBD stricture was characterized by strong enhancement or high attenuation during the delayed phase followed by the portal phase and then the arterial phase. We also found that malignant biliary strictures (MBSs) were longer (25.11 mm vs. 13.18 mm), had CBD wall thickness >1.5 mm, ductal diameter proximal to the stricture (17.93 mm vs. 14.41 mm), had irregular margins, and there was a presence of invasion into the neighboring tissues as compared to BBSs. No significant difference between MBSs and BBSs in regard to the location of the stricture was found. The results of this study correlated well with those of previous studies, which showed that malignant CBD strictures show hyperenhancement on CECT scans or MRI, as well as a thickened wall and a relatively longer segment. ,,,
This ambispective study was done in the CT department of the First Affiliated Hospital of Zhengzhou University, Henan, China. A computerized search of the hospital's radiology and pathology files from January 1, 2008 to December 31, 2010 revealed 200 patients found to be suffering from obstructive jaundice. Patients with liver function tests suggestive of obstructive jaundice and an ultrasound showing biliary obstruction were included in the study. Patients in whom a CECT was not performed, obstructive jaundice not confirmed by means of laboratory tests or direct cholangiography, patients who had undergone biliary interventional procedures, such as biliary stent insertion, endoscopic biliary drainage, or percutaneous transhepatic biliary drainage, and biopsy done prior to CT study were excluded. This summed up to 150 patients.
Informed patient consent
To assess the statistical parameters, SPSS 18.0 software (SPSS version 18.0. Chicago: SPSS Inc) was used. Independent sample t-test was used to determine whether values were normally distributed. Statistical differences in the CT features of malignant and benign strictures were analyzed with the Chi-square test. For all tests, P < 0.05 was considered statistically significant.
Familiarity with the radiological appearances of the duct lumen, wall, and surrounding structures is also important for accurate image interpretation.  Intraductal USG and percutaneous biliary endoscopy are promising new modalities for the diagnosis and treatment of biliary strictures.  CT is known to be more accurate for demonstrating the location and extent of the involved CBD than MRCP and ERCP.  We believe that CT evaluation of the extent of CBD cancer is sometimes limited by pancreatic enhancement, which can mask bile duct enhancement or microscopic infiltration by CC, the latter of which causes subtle changes in enhancement pattern. The diagnostic accuracy of MDCT for tumor location and vertical invasion was satisfactory, but ductal spread was underestimated in comparison with microscopic measurements.