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lu1
ucu1it Gümele1
1 Department of Radiology, Karadeniz Technical University, Faculty of Medicine,
Trabzon 61080, Turkey.
2 Department of Gastroenterology and Hepatology, Karadeniz Technical University,
Faculty of Medicine, Trabzon 61080, Turkey.
3 Department of Surgery, Karadeniz Technical University, Faculty of Medicine,
Trabzon 61080, Turkey.
Received January 26, 2004;
accepted after revision April 20, 2004.
Address correspondence to A. Ahmetolu.
Abstract
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SUBJECTS AND METHODS. MDCT was performed in 34 patients who were thought to have biliary obstruction. Portal venous phase scanning was initiated 70 sec after the IV infusion of 150 mL of contrast agent, and no cholangiographic contrast agent was administered. Three-dimensional MDCT cholangiographic images were produced using volume rendering. ERCP was performed in 26 patients, and percutaneous transhepatic cholangiography (PTC) was performed in five patients; 17 patients underwent biopsy or surgery. The findings on MDCT cholangiography were compared with those of ERCP, PTC, biopsy, or surgery.
RESULTS. The correct diagnosis was made on MDCT cholangiography for 14 (93%) of the 15 patients with a biliary stone and in 16 (94%) of the 17 patients with malignant biliary obstruction. Microlithiasis in one patient could not be detected on MDCT cholangiography. One patient with polypoid adenocarcinoma and one patient with normal findings were incorrectly diagnosed with a biliary stone on the basis of MDCT cholangiography. In one of the two patients with a benign stricture, the stricture was incorrectly diagnosed as malignant. For the diagnosis of biliary stone, sensitivity and specificity of MDCT cholangiography were 93% and 89%, respectively. For the diagnosis of malignant obstruction, sensitivity and specificity were both 94%. The accuracy of the technique for the diagnosis of the cause of biliary obstruction was 83.3%.
CONCLUSION. MDCT cholangiography with volume rendering is a noninvasive and fast imaging technique with high sensitivity and specificity for the diagnosis of the cause of biliary tree obstruction. It is a promising diagnostic tool for the assessment of patients with bile duct obstructions.
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Recently, MDCT has been introduced into clinical practice. It allows faster scanning, which decreases motion and breathing artifacts, as well as thinner collimation. MDCT collects volumetric data that lead to improved 3D assessment of vascular structures and the biliary tree. The display of volume-rendered data reveals a biliary tree with higher attenuation than surrounding tissues. The resulting images are similar to conventional cholangiographic images but are acquired without the use of biliary contrast agents [7]. The aim of this study was to evaluate the diagnostic utility of 3D MDCT cholangiography with volume rendering in patients with suspected obstructive biliary disease.
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All the patients underwent MDCT (Somatom Plus 4, Volume Zoom, Siemens) using the following parameters: collimation, 4 x 1 mm; slice width, 1.25 mm; reconstruction interval, 1 mm; 120 mAs; and 140 kV. We administered 500 mL of water orally 10-15 min before the examination. No biliary contrast agent was administered. A posteroanterior scout view was obtained to set the scanning area. Scanning was performed from the hepatic dome to the level of the L3 vertebra. Portal venous phase scans were obtained 70 sec after the start of IV infusion of 150 mL of iopamidol (Iopamiro 300, Bracco Diagnostics) with 300 mg I/mL through an antecubital vein at rate of 3.5 mL/sec, using a power injector (Medrad). All the source images were transferred to the workstation (Virtuoso, Siemens).
Volume rendering was used to produce MDCT cholangiographic images. Rendering parameters were as follows: window level setting, from -20 to -40 H; window width setting, from -200 to -250 H; opacity, 50-80; and brightness, 20-50. These parameters resulted in images in which the biliary tree appeared hyperdense and in which the hyperdense structures that could interfere with evaluation of the biliary tree (e.g., the vasculature and bones) were eliminated. The same MDCT data as those used for the MDCT cholangiographic images were used to produce MDCT venographic images for those patients with pancreatic masses detected on the axial scans. Venographic images were obtained by adjusting the rendering parameters to highlight the high-attenuation intravascular iodinated contrast agent.
Two experienced radiologists who were unaware of the ERCP and PTC findings evaluated the axial source images, MDCT cholangiographic images, and MDCT venographic images by consensus. They evaluated the presence and rated the degree (mild, moderate, or severe) of biliary tree dilatation subjectively and also identified the site and cause of the obstruction. On MDCT cholangiography, biliary stone was suggested by the appearance of a hypodense filling defect surrounded by hyperdense bile in the bile duct. A malignant tumor was suggested by the visualization of an abrupt irregular narrowing or obstruction in the bile duct. A benign stricture was suggested by the presence of smooth narrowing in a short segment of the bile duct.
ERCP was performed in 26 patients and PTC was performed in five patients within 48 hr of the MDCT examination. The decision as to which patients should undergo ERCP or PTC was made by clinicians. Three patients underwent surgery on the basis of MDCT cholangiographic findings without any further diagnostic procedure. Both a gastroenterologist and a radiologist, blinded to the MDCT cholangiographic findings, evaluated the ERCP and PTC images. The presence and degree (mild, moderate, or severe) of biliary tract dilatation were decided by consensus. The site and the cause of the obstruction were also decided by consensus.
Tissue for cytologic and histologic evaluation was obtained by endoscopically guided biopsy during ERCP in three patients, by percutaneous biopsy in nine patients, and during surgery in seven patients. Sensitivity, specificity, and accuracy of MDCT cholangiography were calculated by comparing the MDCT data with the data obtained with invasive procedures including ERCP, PTC, percutaneous biopsy, and surgical intervention.
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MDCT cholangiographic images in all patients were of diagnostic quality. Thirty-three (97%) of 34 patients were shown to have biliary tree dilatation on MDCT cholangiography. Dilatation was mild in four patients (12%), moderate in 10 patients (30%), and severe in 19 patients (58%). On MDCT cholangiography, observers detected four obstructions of common hepatic duct or bifurcation (or both) and 29 common bile duct obstructions. Findings of MDCT cholangiography are summarized in Table 1, and findings of MDCT cholangiography compared with the final diagnoses are summarized in Tables 2 and 3.
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On MDCT cholangiography, choledocholithiasis was diagnosed in 16 of the 34 patients. The smallest stone observed on MDCT cholangiography was 4 mm. Nine patients had one, three patients had two, and four patients had more than two stones in the common bile duct on MDCT cholangiography (Fig. 1). Two of these 16 patients also had concomitant narrowing in the distal common bile duct. In one patient, a smooth narrowing in a short segment of the common bile duct was diagnosed as a benign stricture (Figs. 2A, 2B). The other patient had an abrupt, irregular narrowing of the distal common bile duct. A diagnosis of a malignant biliary stricture with concomitant choledocholithiasis was considered for this patient. Malignant biliary obstruction was diagnosed in 17 of the 34 patients on MDCT cholangiography. Thirteen of these patients had an obstruction in the common bile duct (Fig. 3), one had an obstruction in the common hepatic duct, and the remaining three patients had an obstruction in the common hepatic duct and bifurcation. One patient had mild dilatation of the common bile duct without any stone or obstruction, and the other patient had normal findings on MDCT cholangiography.
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On ERCP, 25 (96%) of 26 patients had biliary tree dilatation. Dilatation was mild in three patients (12%), moderate in nine (36%), and severe in 13 (52%). On ERCP, diagnosis of choledocholithiasis was established in 10 patients; choledocholithiasis with benign biliary stricture, in one patient; and choledocholithiasis with malignant biliary stricture, in one patient (surgery revealed benign stricture in this patient). Malignant biliary obstruction was diagnosed in 12 patients on ERCP.
PTC was performed in five patients. Four of these patients had severe dilatation in the intrahepatic ducts or common hepatic duct without any dilatation in the common bile duct, and the other patient had severe dilatation in the common bile duct. Diagnosis of malignant biliary obstruction was established in these patients on PTC.
Final diagnosis of the biliary stone was established in 15 patients (12 patients with ERCP and three patients with surgery). Malignant biliary stricture was established in 17 patients (five patients with PTC and 12 patients with ERCP) and was confirmed via endoscopically guided biopsy during ERCP in three patients (three cholangiocarcinomas), via percutaneous biopsy in nine patients (five pancreatic tumors, three Klatskin's tumors, and one gallbladder tumor), and via surgery in five patients (four cholangiocarcinomas and one polypoid adenocarcinoma). Final diagnosis of a benign biliary stricture was established in two patients (with surgery in one patient and with ERCP in the other) who also had a biliary stone. One patient who had mild dilatation in the biliary tree on ERCP was thought to have passed a stone, and one patient had normal findings.
On MDCT cholangiography, the radiologists correctly diagnosed a biliary stone in 14 of the 15 patients with stones and had one false-negative and two false-positive results. One patient had mild dilatation in the common bile duct without any stone on MDCT cholangiography, but a small stone was extracted endoscopically during ERCP. One patient had a filling defect in the common bile duct that was diagnosed as choledocholithiasis on MDCT cholangiography. In this patient, ERCP also revealed a filling defect in the common bile duct that was thought to be choledocholithiasis. However, because the lesion could not be extracted with a nitinol basket, it was thought to be polypoid mass. The patient underwent surgery during which a polypoid mass was observed, and the pathologic diagnosis of the mass was polypoid adenocarcinoma. On MDCT cholangiography, one patient was found to have multiple hypodense filling defects with mild dilatation in the common bile duct that suggested a biliary stone. ERCP showed mild dilatation in the common bile duct, but no stone was observed. Retrospective analysis of the axial images revealed no stone but did show a hyperdense gastroduodenal artery crossing over the common bile duct. The hypodense filling defects on MDCT cholangiography were concluded to be due to superimposed gastroduodenal artery, which was confirmed on MDCT angiography (Figs. 4A, 4B). Sensitivity and specificity of MDCT cholangiography for the diagnosis of biliary stone in our study were 93.3% and 89.5%, respectively.
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On MDCT cholangiography, the radiologists correctly diagnosed malignant biliary obstruction in 16 of the 17 patients with such an obstruction and had one false-positive and one false-negative result. In one patient, polypoid adenocarcinoma in the common bile duct was incorrectly diagnosed as a biliary stone, and in one patient, a benign stricture was incorrectly diagnosed as a malignant biliary stricture. Sensitivity and specificity of MDCT cholangiography for the diagnosis of malignant biliary obstruction in our study were 94.1% and 94.1%, respectively. MDCT cholangiography correctly diagnosed normal findings in one of the two patients who had no stone, malignancy, or benign stricture on ERCP. Overall accuracy, which was calculated as the number of correct diagnoses divided by the total number of diagnoses, of MDCT cholangiography for the diagnosis of all causes of biliary obstruction was 83.3%.
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ERCP has some advantages over the other noninvasive techniques for the evaluation of biliary obstructions. It provides both a diagnosis and therapeutic intervention in the same setting. Once stones are identified and the diagnosis is established, endoscopic sphincterotomy and stone extraction can be performed immediately. In mass lesions, endoscopically guided biopsy can be performed to establish the diagnosis. However, ERCP provides little information about the solid organs of the abdomen, and because it is an invasive technique, it has a 0.5-5.0% rate of complications, including adverse reaction to sedatives, cardiorespiratory dysfunction, pancreatitis, perforation of the gastrointestinal tract, bleeding, cholangitis, sepsis, and death [10, 11].
Although axial CT is useful for the evaluation of the pancreas and biliary tree in patients with obstructive biliary disease, the cross-sectional orientation of the CT scans makes it less accurate for revealing complex anatomic relationships. Evaluation of choledocholithiasis is further impaired in stones with attenuation similar to that of bile. Reported sensitivities of unenhanced CT for detection of lithiasis range from 25% to 90% [8, 12]. A number of helical CT studies performed to evaluate the biliary tree have used an oral or IV biliary contrast agent [2, 13, 14]. However, the biliary contrast agent was not useful in patients with an elevated bilirubin level because the liver could not extract and excrete the contrast agent into the biliary system [2, 3, 4]. Administration of an IV cholangiographic contrast agent has caused some severe adverse reactions [3, 15, 16]. A second examination with an IV contrast agent is necessary to characterize suspected lesions of the liver or the pancreas. Moreover, unenhanced CT should be performed because hyperdense stones could be missed within the opacified bile duct, which raises the radiation dose [2, 13, 14].
Only a few studies of MDCT cholangiography performed without biliary contrast agent appear in the literature [7, 17]. Zandrino et al. [17] used minimum intensity projection to produce MDCT cholangiographic images and reported that MDCT cholangiography could be used to correctly assess the level of bile duct obstruction and allow a fairly accurate diagnosis of the cause of the obstruction. They also concluded that the absence of bile duct dilatation reduces the sensitivity for stone detection, and small isoattenuating stones may not be detected on MDCT cholangiography. Johnson et al. [7] produced MDCT cholangiographic images using volume rendering in four patients with a pancreatic tumor. These researchers reported that MDCT with volume rendering is a versatile technique and that by modifying display parameters, it can be used to reveal the site and cause of biliary obstruction and vascular invasion by tumor during a preoperative evaluation. However, they did not evaluate any patient with a biliary tumor or stone in their study.
MDCT cholangiography with volume rendering has some advantages over CT cholangiography with biliary contrast agent, ERCP, and PTC. First, MDCT cholangiography performed without a biliary contrast agent eliminates complications related to the use of the biliary contrast agent. The technique could be used in those patients with an elevated bilirubin level or abnormal liver function. The biliary tree can be rotated in any orientation so that all the intrahepatic ducts may be viewed, which is not possible on ERCP or PTC. The same data set may be used to produce angiographic images to evaluate for vascular invasion by tumors. In our study, we performed MDCT venography in five patients who had a pancreatic mass visible on the axial images. Portal vein and superior mesenteric vein invasion by pancreatic carcinoma was revealed in two patients on MDCT venography (Figs. 5A, 5B). MDCT with volume rendering allows an overall assessment of patients with biliary obstruction by depicting the biliary tree, vessels, and abdominal solid organs such as the liver, pancreas and duodenum, that could not be evaluated on ERCP and PTC.
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In one of our patients with Klatskin's tumor, the left intrahepatic duct shown on MDCT cholangiography could not be seen on PTC because it was totally obstructed by the tumor. Patients with hilar cholangiocarcinoma may have an isolated hepatic segment. In this patient, the isolated intrahepatic bile duct segment could not be opacified on ERCP or PTC. Drainage of the larger segment may provide symptomatic relief in such patients. MDCT cholangiography could reveal these isolated bile duct segments and may be helpful for planning the drainage of the segment that would most beneficial for the patient.
Volume-rendering parameters used in our study show the biliary tree as a hyperdense structure and eliminate hyperdense structures that could interfere with evaluation of biliary tree, such as the vasculature and bones. However, this technique has some drawbacks. Biliary stones appear as hypodense filling defects when compared with bile on MDCT cholangiography. Vascular structures also appear hypodense, and small vessels that are superimposed to the common bile duct, such as the gastroduodenal artery, could be misdiagnosed as a biliary stone. Evaluation of the axial images could eliminate misinterpretation of small vessels as a stone. Theoretically, this technique could not be used to differentiate isoattenuating stones from the bile, even if thin collimation is used, because both bile and isoattenuating stone have the same density and appear hyperdense. Difficulty in detecting small stones is another drawback of the MDCT cholangiography. In our study, the smallest stone on MDCT cholangiography was 4 mm, and in one patient, microlithiasis could not be diagnosed on MDCT cholangiography. Our study included only 15 patients who had biliary stones. The small number of patients with a biliary stone, the lack of isoattenuating stones, and the small number of patients (one patient) with a nondilated biliary tree may have led to the high sensitivity and specificity of MDCT cholangiography for revealing biliary stones in our study.
We found that MDCT cholangiography showed malignant biliary obstruction in 16 of 17 patients with such obstructions (94%). In one patient, a benign stricture was incorrectly diagnosed as a malignant biliary stricture. It is not always possible to distinguish benign from malignant biliary stenosis even on ERCP [18]. Obtaining a tissue diagnosis during ERCP may still be required in indeterminate cases, although the results of ERCP-based tissue diagnosis are imperfect [18]. Polypoid adenocarcinoma in the common bile duct was incorrectly diagnosed on MDCT cholangiography as a biliary stone in one patient. The lesion was slightly hyperdense on the axial images. Papillary tumors and bile duct stones manifest as soft-tissue masses with high or low attenuation on the axial CT scans. Unenhanced CT is helpful for differentiating bile stones from polypoid masses because tumors attached to the wall of the bile duct enhance [19]. In our study, we did not obtain unenhanced axial scans, and therefore we could not evaluate contrast enhancement of the lesion.
Johnson et al. [7] reported that low contrast between the intrahepatic duct and the contrast-enhanced liver was the main disadvantage of MDCT cholangiography with volume rendering. Maximal hepatic enhancement is one of the most important factors for CT cholangiography. In the study by Johnson et al., portal venous phase scanning was initiated 50 sec after the onset of contrast administration, but peak hepatic enhancement occurs approximately 75 sec after contrast initiation [20]. In our study, portal venous phase scans were obtained 70 sec after the onset of contrast administration. The difference in contrast between the intrahepatic biliary tree and the enhanced liver parenchyma is still not enough to obtain conventional cholangiographic-like images of the intrahepatic segment on MDCT cholangiography. We did not evaluated the effect of fatty liver on the quality of MDCT cholangiographic images, but hepatic steatosis may also reduce contrast difference between hepatic parenchyma and intrahepatic bile ducts in middle-aged patients.
In conclusion, MDCT cholangiography with volume rendering is noninvasive and fast and has high sensitivity and specificity for the diagnosis of benign and malignant causes of biliary obstruction. Although it has some limitations, MDCT cholangiography with volume rendering is a promising diagnostic tool and may be used as an alternative to ERCP or PTC in the assessment of the patients with bile duct obstructions when MR cholangiography cannot be performed.
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