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Detection of Biliary Duct Narrowing and Choledocholithiasis: Accuracy of Portal Venous Phase Multidetector CT¹

¹ From the Department of Radiology, Boston University Medical Center, 88 E Newton St, 2nd floor, Boston, MA 02215. Received March 12, 2007; revision requested May 17; revision received June 25; accepted July 19; final version accepted October 15. Address correspondence to S.W.A. (e-mail: Stephan.Anderson{at}bmc.org).

	ABSTRACT

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION ADVANCES IN KNOWLEDGE IMPLICATIONS FOR PATIENT CARE References

 
Purpose: To retrospectively evaluate the sensitivity and specificity of 64-detector computed tomography (CT) in the portal venous phase by using transverse images and both multiplanar and minimum intensity reformations for the detection of biliary duct narrowing and choledocholithiasis, with magnetic resonance cholangiopancreatography (MRCP) or endoscopic retrograde cholangiopancreatography (ERCP) as the reference standard.

Materials and Methods: Approval from institutional review board was obtained for this HIPAA-compliant retrospective study; informed consent was waived. The study included all patients (42 men, 52 women; mean age, 61 years) who underwent abdominal 64-detector CT within 2 months of MRCP and/or ERCP. All patients underwent portal venous phase intravenous contrast material–enhanced abdominal CT. Sixty-one patients underwent MRCP and 54 patients underwent ERCP (21 patients underwent both). Two radiologists, blinded to the reference standard, independently evaluated the CT images, including multiplanar and minimum intensity reformations, for biliary duct narrowing and choledocholithiasis. Standard of reference examinations were used to calculate sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV).

Results: Twenty-three (24%) of 94 patients had a biliary duct narrowing at reference examinations. For detecting biliary duct narrowing, observer 1 had a sensitivity of 78.2%, specificity of 100%, PPV of 100%, and NPV of 93.4% and observer 2 had a sensitivity of 69.6%, specificity of 100%, PPV of 100%, and NPV of 91.0%. In 18 (19%) of 94 patients, choledocholithiasis was detected at reference examinations. For detecting choledocholithiasis, observer 1 had a sensitivity of 77.8%, specificity of 96.1%, PPV of 82.4%, and NPV of 94.8% and observer 2 had a sensitivity of 72.2%, specificity of 96.1%, PPV of 81.2%, and NPV of 93.6%.

Conclusion: Portal venous phase multidetector CT images are highly specific and moderately sensitive for the detection of biliary duct narrowing and choledocholithiasis.

© RSNA, 2008

	INTRODUCTION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION ADVANCES IN KNOWLEDGE IMPLICATIONS FOR PATIENT CARE References

 
Currently, in patients clinically suspected of having diseases referable to the biliary tract, the most often used noninvasive imaging modality is ultrasonography (US), often followed by magnetic resonance (MR) and MR cholangiopancreatography (MRCP) (1–6). However, the use of computed tomography (CT) has increased exponentially in recent years, especially in patients with nonspecific abdominal complaints (7,8). The technique used for abdominal CT scans acquired for nonbiliary indications is often not ideal for detecting certain biliary diseases, including ductal narrowing and choledocholithiasis. Nonenhanced and pancreatic-phase images are not always part of abdominal CT protocols performed for nonbiliary indications (9).

The ability to acquire isotropic datasets has made CT a multiplanar modality. Multiplanar reformations, including standard orthogonal, coronal, and sagittal planes, as well as nonstandard oblique and curved-linear planes, are particularly useful in evaluating biliary disease (10–12). Additional postprocessing tools, such as minimum intensity projections, have been utilized to improve the accuracy of biliary tract imaging (10–13). The purpose of our study was to retrospectively evaluate the sensitivity and specificity of 64-detector CT in the portal venous phase by using transverse images and both multiplanar and minimum intensity reformations for the detection of biliary duct narrowing and choledocholithiasis, with MRCP or endoscopic retrograde cholangiopancreatography (ERCP) as the reference standard.

	MATERIALS AND METHODS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION ADVANCES IN KNOWLEDGE IMPLICATIONS FOR PATIENT CARE References

 
Patients
Approval from our institutional review board was obtained for this retrospective Health Insurance Portability and Accountability Act–compliant study; informed consent was waived. This study included all patients who underwent intravenous contrast material–enhanced 64-detector CT of the abdomen with positive oral contrast material between June 7, 2005, and August 20, 2006, and who also underwent MRCP and/or ERCP within 2 months of the CT scan (either before or after). This included 94 patients (42 men, 52 women) with a mean age of 61 years (mean age of men, 60 years; mean age of women, 62 years). Fourteen (15%) of 94 patients underwent a multiphasic CT, which included precontrast and arterial phase images.

In addition to CT, 61 patients underwent MRCP and 54 patients underwent ERCP (21 patients underwent both). The mean time between the standard of reference examination and CT was 14 days (median, 3 days; range, 0–60 days). The clinical indications for the CT examination were as follows: abdominal pain (n = 53), follow-up examination in a patient with known malignancy (n = 12), jaundice (n = 11), fever of unknown origin (n = 5), abnormal liver function tests (n = 3), and other (n = 10). The clinical indications that resulted in other tests being performed, including MRCP and/or ERCP examinations, were as follows: biliary abnormality at CT (n = 61), laboratory test abnormalities (n = 16), and other (n = 19).

CT Technique
CT examinations were performed by using a 64-detector CT scanner (Lightspeed VCT; GE Medical Systems, Milwaukee, Wis). Portal venous phase CT examinations were performed from the diaphragm to the greater trochanters with the following parameters: a section thickness of 1.25 mm, a reconstruction interval of 1.25 mm, a pitch of 1:0.987, a noise factor of 19 (automatic dose modulation), and a gantry rotation time of 0.5 second. The direct multiplanar reformation function was used to generate coronal and sagittal reformations with a section thickness of 2.5 mm and a reconstruction interval of 2.5 mm.

All patients received intravenously 100 mL of ioversol (350 mg of iodine per milliliter, Optiray; Mallinckrodt Imaging, Hazelwood, Mo) injected through a cannula in an antecubital or hand vein at a rate of 4 mL/sec by using a power injector. We routinely use a dual-syringe power injector (Stellant CT Injection System; Medrad, Indianola, Pa) to administer a 30 mL of normal saline solution as a chasing bolus immediately after intravenous contrast material injection. The saline bolus was injected at 4 mL/sec. Acquisition of arterial and portal venous phase images started 30 and 70 seconds, respectively, after the initiation of the contrast material injection. All studies were performed with oral contrast material, per our routine abdominal imaging protocols (900 mL of 2.2% barium sulfate suspension, Medescan; Lafayette Pharmaceuticals, Lafayette, Ind).

Image Analysis
Two radiologists (S.W.A., E.R.) blinded to the reference data, as well as the official prospective CT interpretations, independently interpreted the portal venous phase images at picture archiving and communication systems workstations (GE Centricity; GE Medical Systems). The radiologists included a senior radiology resident (S.W.A.) and an attending radiologist (E.R.) with 6 years of abdominal CT interpretation experience. The radiologists received randomized CT scans of all patients and were asked to evaluate focal narrowing affecting the intra- or extrahepatic biliary tract. A diagnosis of narrowing was made when there was an abrupt change in the bile duct caliber, whether or not there was any evidence of biliary dilatation. The radiologists also indicated whether the narrowing was likely secondary to a malignant or a benign etiology. A diagnosis of malignant biliary narrowing was made when a mass involving or surrounding the bile duct was seen or when focal nodular biliary wall thickening was present in the region of the stricture (14,15). Secondary signs increasing the likelihood of malignant biliary narrowing included evidence of malignant disease elsewhere in the abdomen. A diagnosis of benign narrowing was made when there was a lack of these features of malignancy (16). When associated with bile duct wall thickening, narrowing was characterized as benign if the narrowing was smooth and gradually tapered.

In addition, the radiologists were asked to evaluate for the presence of choledocholithiasis. A diagnosis of choledocholithiasis was made when there was direct visualization of a stone as a diffusely calcified, peripherally calcified, or a focus of soft-tissue attenuation within the bile duct, either partially or completely surrounded by bile—crescent sign and target sign, respectively (1). The radiologists were encouraged to use window settings as judged appropriate for the detection of bile duct stones. The radiologists were also asked to determine the imaging characteristics of the biliary stones, when identified, as diffusely calcified, partially calcified, or of soft-tissue attenuation. The radiologists also noted whether gallbladder stones were present in those patients who had common duct stones.

The radiologists interpreted the studies using transverse, sagittal, and coronal images. In addition, they had the option to use postprocessing tools available with the picture archiving and communication systems–integrated three-dimensional software (Advantage Windows Suite; GE Medical Systems), especially minimum intensity and curved-linear reformations.

After the initial independent interpretations, the radiologists were unblinded to the results of the standard of reference examinations. They jointly reviewed CT studies that yielded any false-positive or false-negative interpretation for detecting biliary duct narrowing and biliary stones. The radiologists determined if, in retrospect, the areas of narrowing and/or stones were visible at CT. Also, for the false-positive examinations, the radiologists provided possible explanations for the incorrect interpretations.

Standard of Reference
The official reports of the MRCP or ERCP examinations were used as the standard of reference. In those patients who underwent both MRCP and ERCP examinations, ERCP results were used as the standard of reference. Thus, the standard of reference was ERCP for 54 patients and MRCP for 40 patients. A review of the patients' electronic medical records was undertaken to determine cytologic or histopathologic results in those patients who underwent brushings for cytology during ERCP, biopsy, or surgical intervention. The reviews of the standard of reference reports, as well as the electronic chart review, were undertaken by a single senior radiology resident (S.W.A.).

Statistical Analysis
The independent interpretations by the radiologists were compared with the standard of reference to determine diagnostic performance parameters for the 64-detector CT. Sensitivity, specificity, positive and negative predictive values, and 95% confidence intervals (CIs) (R statistical system, version 2.0.1; R Foundation for Statistical Computing, Vienna, Austria) were calculated. A true-positive interpretation was defined as one in which the observer(s) identified a biliary duct narrowing at CT and the standard of reference examination identified a narrowing in the same location. A false-positive interpretation was defined as one in which the observer(s) identified a biliary duct narrowing at CT that was not confirmed with the standard of reference. A true-negative interpretation was defined as one in which the observer(s) did not identify an area of narrowing at CT and the standard of reference showed no narrowing. A false-negative interpretation was defined as one in which the observer(s) did not identify biliary duct narrowing at CT, but a narrowing was found on the standard of reference study. In addition, diagnostic performance was calculated for the detection of narrowing secondary to malignant etiology. For this purpose, a misinterpretation of a malignant narrowing as a benign stricture was considered a false-negative interpretation, whereas the misinterpretation of a benign narrowing as a malignant narrowing was classified as a false-positive interpretation.

The diagnostic performance was also calculated for the detection of choledocholithiasis by using similar definitions. Ninety-five percent CIs for each one of these parameters of diagnostic performance were calculated. This analysis was performed separately for each radiologist. The agreement between the two observers for detecting biliary duct narrowing and the presence of choledocholithiasis was calculated by using statistics. Agreement was classified as follows: poor, = 0.00–0.20; fair, = 0.21–0.40; moderate, = 0.41–0.60; good, = 0.61–0.80; and very good, = 0.81–1.00.

Sensitivity, specificity, positive predictive value, and negative predictive value were calculated for the prospective official CT reports both for the findings of biliary duct narrowing and choledocholithiasis. These reports were compared with the standard of reference, as was done with the retrospective interpretations by the blinded observers. Depending on the inclusion of a diagnosis of a focal narrowing or stone in the official report, these prospective interpretations were defined as true-positive, false-positive, true-negative, or false-negative. Of note, unenhanced and hepatic arterial phase series were available for the prospective interpretation in 14 (15%) of the 94 patients.

	RESULTS

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Biliary Strictures
In 23 (24%) of the 94 patients, single areas of biliary duct narrowing were diagnosed at the standard of reference examination (Fig 1). In 17 (74%) of the 23 patients, the areas of biliary duct narrowing had a malignant cause and in six (26%) patients they had a benign cause. The mean interval between the CT examinations and MRCP or ERCP for the patients with a biliary duct narrowing was 5 days (range, 0–27 days).

View larger version (18K): [in this window] [in a new window] [Download PPT slide]   Figure 1: Flowchart depicts observer performance in diagnosing biliary strictures.

For detecting biliary duct narrowing (both benign and malignant), the prospective evaluations, as recorded by the officially dictated reports, resulted in 69 true-negative, 13 true-positive, 10 false-negative, and two false-positive interpretations. The diagnostic performance for the prospective evaluations was a sensitivity of 56.5% (95% CI: 34.9%, 76.1%), specificity of 97.2% (95% CI: 89.3%, 99.5%), positive predictive value of 86.7% (95% CI: 58.4%, 97.7%), and negative predictive value of 87.3% (95% CI: 77.5%, 93.4%).

Malignant Strictures
Seventeen patients had malignant biliary duct narrowing: in eight caused by pancreatic ductal adenocarcinoma, in three caused by cholangiocarcinoma (a single hepatic hilar lesion and two suprapancreatic lesions), in five caused by metastatic disease affecting either periportal or perihilar lymph nodes (two patients) or the liver parenchyma (three patients), and in one a stricture caused by a biliary tubulovillous adenoma within the central intrahepatic ducts (Fig 2).

View larger version (163K): [in this window] [in a new window] [Download PPT slide]   Figure 2a: Images in 70-year-old woman with a history of lung cancer and with pancreatitis. (a) Coronal minimum intensity projection demonstrates focal narrowing (arrow) within the mid-common bile duct. (b) Transverse CT image demonstrates numerous liver metastases and a necrotic-appearing lymph node (arrow) immediately adjacent to the patient's stricture. (c) Oblique coronal image of multisection single-shot MRCP (repetition time msec/echo time msec, 1150/650) confirms biliary duct narrowing (arrow). The narrowing was secondary to a malignant invasion from the adjacent mass or the metastatic lymph node.

View larger version (150K): [in this window] [in a new window] [Download PPT slide]   Figure 2b: Images in 70-year-old woman with a history of lung cancer and with pancreatitis. (a) Coronal minimum intensity projection demonstrates focal narrowing (arrow) within the mid-common bile duct. (b) Transverse CT image demonstrates numerous liver metastases and a necrotic-appearing lymph node (arrow) immediately adjacent to the patient's stricture. (c) Oblique coronal image of multisection single-shot MRCP (repetition time msec/echo time msec, 1150/650) confirms biliary duct narrowing (arrow). The narrowing was secondary to a malignant invasion from the adjacent mass or the metastatic lymph node.

View larger version (108K): [in this window] [in a new window] [Download PPT slide]   Figure 2c: Images in 70-year-old woman with a history of lung cancer and with pancreatitis. (a) Coronal minimum intensity projection demonstrates focal narrowing (arrow) within the mid-common bile duct. (b) Transverse CT image demonstrates numerous liver metastases and a necrotic-appearing lymph node (arrow) immediately adjacent to the patient's stricture. (c) Oblique coronal image of multisection single-shot MRCP (repetition time msec/echo time msec, 1150/650) confirms biliary duct narrowing (arrow). The narrowing was secondary to a malignant invasion from the adjacent mass or the metastatic lymph node.

View larger version (159K): [in this window] [in a new window] [Download PPT slide]   Figure 3a: Images in 81-year-old woman with fever, nausea, and vomiting. (a) Coronal and (b) sagittal minimum intensity projection CT images demonstrate a focal narrowing (arrow) involving the distal common bile duct. Note the smooth margins of the stricture without evidence of abnormal soft-tissue thickening. (c) Oblique coronal image of multisection single-shot MRCP (1150/650) confirms the presence of a focal narrowing (arrow) within the distal common duct. This was a benign stricture, likely secondary to the patient's history of pancreatitis.

View larger version (136K): [in this window] [in a new window] [Download PPT slide]   Figure 3b: Images in 81-year-old woman with fever, nausea, and vomiting. (a) Coronal and (b) sagittal minimum intensity projection CT images demonstrate a focal narrowing (arrow) involving the distal common bile duct. Note the smooth margins of the stricture without evidence of abnormal soft-tissue thickening. (c) Oblique coronal image of multisection single-shot MRCP (1150/650) confirms the presence of a focal narrowing (arrow) within the distal common duct. This was a benign stricture, likely secondary to the patient's history of pancreatitis.

View larger version (122K): [in this window] [in a new window] [Download PPT slide]   Figure 3c: Images in 81-year-old woman with fever, nausea, and vomiting. (a) Coronal and (b) sagittal minimum intensity projection CT images demonstrate a focal narrowing (arrow) involving the distal common bile duct. Note the smooth margins of the stricture without evidence of abnormal soft-tissue thickening. (c) Oblique coronal image of multisection single-shot MRCP (1150/650) confirms the presence of a focal narrowing (arrow) within the distal common duct. This was a benign stricture, likely secondary to the patient's history of pancreatitis.

Choledocholithiasis
In 18 (19%) of 94 patients, choledocholithiasis was diagnosed at the standard of reference examination (Fig 4). All patients with proved choledocholithiasis underwent ERCP with stone removal. At ERCP, the common bile duct stones were all found to be in the distal common bile duct. The mean time between CT and ERCP examination was 10 days (range, 0–51 days) for the patients with choledocholithiasis.

View larger version (18K): [in this window] [in a new window] [Download PPT slide]   Figure 4: Flowchart depicts observer performance in diagnosing choledocholithiasis.

View larger version (160K): [in this window] [in a new window] [Download PPT slide]   Figure 5a: Images in 94-year-old woman with abdominal discomfort. (a) Coronal and (b) sagittal minimal intensity projection CT images demonstrate two large common bile duct stones (arrow). (c) ERCP confirms the presence of choledocholithiasis (arrows).

View larger version (162K): [in this window] [in a new window] [Download PPT slide]   Figure 5b: Images in 94-year-old woman with abdominal discomfort. (a) Coronal and (b) sagittal minimal intensity projection CT images demonstrate two large common bile duct stones (arrow). (c) ERCP confirms the presence of choledocholithiasis (arrows).

View larger version (167K): [in this window] [in a new window] [Download PPT slide]   Figure 5c: Images in 94-year-old woman with abdominal discomfort. (a) Coronal and (b) sagittal minimal intensity projection CT images demonstrate two large common bile duct stones (arrow). (c) ERCP confirms the presence of choledocholithiasis (arrows).

View larger version (172K): [in this window] [in a new window] [Download PPT slide]   Figure 6a: Images in 51-year-old man with abdominal pain. Standard (a) coronal and (b) sagittal CT images demonstrate extrahepatic bile ducts without evidence of stones (arrows). (c) ERCP image demonstrates evidence of choledocholithiasis (arrow).

View larger version (158K): [in this window] [in a new window] [Download PPT slide]   Figure 6b: Images in 51-year-old man with abdominal pain. Standard (a) coronal and (b) sagittal CT images demonstrate extrahepatic bile ducts without evidence of stones (arrows). (c) ERCP image demonstrates evidence of choledocholithiasis (arrow).

View larger version (151K): [in this window] [in a new window] [Download PPT slide]   Figure 6c: Images in 51-year-old man with abdominal pain. Standard (a) coronal and (b) sagittal CT images demonstrate extrahepatic bile ducts without evidence of stones (arrows). (c) ERCP image demonstrates evidence of choledocholithiasis (arrow).

View larger version (175K): [in this window] [in a new window] [Download PPT slide]   Figure 7a: Images in 75-year-old woman with abnormal liver enzymes. (a) Transverse and (b) coronal CT images demonstrate subtle findings of biliary stone (arrow) within the distal common duct as evidenced by hyperattenuating periphery. ERCP (not shown) confirmed the presence of a common duct stone. This examination was a false-negative interpretation for one of the observers.

View larger version (166K): [in this window] [in a new window] [Download PPT slide]   Figure 7b: Images in 75-year-old woman with abnormal liver enzymes. (a) Transverse and (b) coronal CT images demonstrate subtle findings of biliary stone (arrow) within the distal common duct as evidenced by hyperattenuating periphery. ERCP (not shown) confirmed the presence of a common duct stone. This examination was a false-negative interpretation for one of the observers.

View larger version (159K): [in this window] [in a new window] [Download PPT slide]   Figure 8a: Images in 72-year-old woman with a history of endometrial carcinoma and a prior sphincterotomy. (a) Coronal and (b) transverse maximum intensity projection CT images demonstrate a hyperattenuating area (arrow) within the distal common bile duct; b also demonstrates a focus of biliary air (arrowhead). Patient underwent ERCP without evidence of biliary stones (not shown). The hyperattenuating area within the common duct at the CT examination was likely secondary to reflux of oral contrast material. The CT finding resulted in a false-positive interpretation for one of the observers.

View larger version (180K): [in this window] [in a new window] [Download PPT slide]   Figure 8b: Images in 72-year-old woman with a history of endometrial carcinoma and a prior sphincterotomy. (a) Coronal and (b) transverse maximum intensity projection CT images demonstrate a hyperattenuating area (arrow) within the distal common bile duct; b also demonstrates a focus of biliary air (arrowhead). Patient underwent ERCP without evidence of biliary stones (not shown). The hyperattenuating area within the common duct at the CT examination was likely secondary to reflux of oral contrast material. The CT finding resulted in a false-positive interpretation for one of the observers.

For detecting choledocholithiasis on the portal venous phase studies, the prospective evaluations, as recorded by the officially dictated reports, resulted in 72 true-negative, 10 true-positive, eight false-negative, and four false-positive interpretations. The diagnostic performance for the prospective evaluations was a sensitivity of 55.6% (95% CI: 31.3%, 77.6%), specificity of 94.7% (95% CI: 86.4%, 98.3%), positive predictive value of 71.4% (95% CI: 42.0%, 90.4%), and negative predictive value of 90% (95% CI: 80.7%, 95.3%).

	DISCUSSION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION ADVANCES IN KNOWLEDGE IMPLICATIONS FOR PATIENT CARE References

 
Multidetector CT has been shown to be accurate for establishing the diagnosis of biliary strictures (10,13,17). Unlike CT cholangiographic methods, where contrast agents are utilized to opacify bile and greatly increase attenuation differences between the bile ducts and the surrounding tissues, detection of stones with routine CT techniques depends on lower attenuation differences. Therefore, the image quality provided with multidetector CT technology becomes especially critical in evaluating the bile ducts. The introduction of 16- and 64-detector CT scanners has resulted in excellent multiplanar capabilities. The ability to evaluate the bile ducts in multiple planes, especially coronal, curved-linear, and oblique planes, increases the ease of visualization of the biliary tree (18). Finally, advanced postprocessing techniques such as minimum intensity reformations generate images that increase the conspicuity of low-attenuation bile ducts against the background of higher-attenuation soft tissues (12,13,18).

By using 64-detector CT in evaluating for biliary duct narrowing, the diagnostic performance we achieved is moderately improved compared with that in prior studies that used single-section technology, which reported sensitivity and specificity of 77% and 63%, respectively (19). The lack of an increase in sensitivity in detecting strictures may be secondary to the study design in that our study population was not limited to patients suspected of having biliary obstruction. Also, our study included benign causes of narrowing, which usually lack wall thickening or mass lesion and may therefore be less apparent at CT, especially as compared with ERCP, which achieves maximum duct distention and exaggerates subtle changes in caliber. Finally, the CT technique used in our study included portal venous phase imaging with positive oral contrast material, which, while commonly used for patients with nonspecific presentations, may not be optimal for biliary tract imaging (9).

The improved specificity for detecting biliary duct narrowing likely results from the ease of detection using both multiplanar and minimum intensity reformations. This specificity suggests that repeat CT examinations with dedicated biliary protocols may be unnecessary when a portal venous phase scan acquired with 64-detector CT technology shows a biliary duct narrowing. Though the reported sensitivity for the detection of biliary strictures with MRCP is slightly better than what we found in our study, the specificity of MRCP may not be much higher than that of portal venous phase multidetector CT (19). The use of additional MR sequences, including contrast-enhanced sequences, though not evaluated in this study, has been shown to be useful for detecting and characterizing biliary strictures (20). Therefore, the need for confirmatory MRCP should be questioned when there is evidence of a focal biliary duct narrowing at multidetector CT. Alternatively, these patients may instead undergo further diagnostic work-up in the form of tissue sampling or definitive intervention with biliary drainage or resection (21,22). Once a malignant lesion is confirmed, additional tests may be required for proper staging, and these may include a dedicated multiphasic CT study. Our study did not address the staging function of multidetector CT.

The sensitivity for the detection of choledocholithiasis achieved in our study remains similar to the results reported by using single-detector and four-detector CT technology (4,23,24). This likely stems from the theoretical limit implicit in the detection of common bile duct stones by using CT secondary to stone composition. Common bile duct stones have been shown to be isoattenuating to bile in up to 20% of patients (25,26). The composition of biliary stones places a limit on the sensitivity of CT performed with a fixed tube voltage and fixed or fluctuating tube current (as in our study) irrespective of spatial and contrast resolution. In these cases of hypoattenuating biliary stones, unenhanced CT often aids in detection. We elected not to analyze the diagnostic accuracy of the subset of precontrast examinations for detecting choledocholithiasis, as the number of patients with unenhanced images was very small (n = 15) and this was not the purpose of the study. Counterintuitively, techniques that increase peak tube voltage settings to increase conspicuity of biliary stones may increase diagnostic accuracies and deserve further research (27).

The specificity achieved in our study for the detection of biliary stones is improved compared with that in prior reports (4,23,24). With the image quality of 64-detector CT technology, as well as multiplanar reformation, the presence of hyperattenuating foci, when perceived within the bile ducts, is less likely to represent a false-positive finding. Previously, adjacent vessels or areas of partial volume averaging with the adjacent hyperattenuating structures, including pancreatic parenchyma, may have lent themselves to false-positive interpretations. In addition, a normal or inflamed bile duct that demonstrates avid enhancement may also yield a false-positive interpretation (28). Currently, such false-positive misinterpretations may be less likely given use of thinner sections with decreased partial volume averaging and multiplanar evaluation.

Since our study included CT examinations completed for various indications, the images were acquired with intravenous and oral contrast material (9). Though the administration of intravenous contrast material may increase the conspicuity of biliary stones in certain cases, it is generally believed that diagnostic accuracy is improved in the absence of intravenous and oral contrast material (24). However, in routine practice, intravenous and oral contrast material is typically administered for CT examinations of patients presenting with nonspecific symptoms, such as abdominal pain. Routine acquisition of nonenhanced series is not commonplace in these circumstances. Though not optimal, the initial opportunity to make a diagnosis of choledocholithiasis may include intravenous and oral contrast material and, therefore, our study likely reflects clinical practice.

The limitations of our study include features inherent in its retrospective design. Namely, the radiologists were instructed to scrutinize the bile ducts for evidence of focal narrowing or stones, an artificial situation typically resulting in improved accuracy as the radiologists are focused on a limited portion of the examination. Therefore, the diagnostic performance achieved by these radiologists reflects what is possible with this specific acquisition technique, but not what may be realistic in prospective evaluation of CT examinations. This point is well demonstrated in our study by the decreased diagnostic accuracy of the prospective, dictated reports when compared with the retrospective review by the two radiologists. Also, the study included patients undergoing CT, as well as MRCP and/or ERCP, within a 2-month period. Therefore, especially in cases of malignant narrowing, the appearance of the lesions on a CT scan when compared with the standard of reference may be somewhat different. Similar limitations apply to the evaluation of choledocholithiasis. Especially in cases of false-positive CT interpretations, lapse in time between CT studies and standard of reference examinations may allow stones to pass in the interim, decreasing diagnostic performance. Also, since many of the patients underwent the standard of reference on the basis of positive findings at CT examinations, verification bias become a limitation of our study (29). Finally, since precontrast images were not available, enhancement characteristics were not available, findings that may be helpful in a more confident differentiation between choledocholithiasis and intraductal neoplasm. However, our study did not reveal cases of misinterpretation of biliary stones as intraductal neoplasm or vice versa.

In conclusion, 64-detector CT technology yields moderately high diagnostic performance in detection of biliary duct narrowing and choledocholithiasis when images are acquired in the portal venous phase of enhancement and a positive oral contrast material is used. Given the diagnostic accuracy of 64-detector CT for the detection of biliary duct narrowing, initial portal venous phase imaging with abdominal-pain CT protocols may be sufficient for diagnosis, especially when CT demonstrates abnormalities such as biliary duct narrowing or stones, since the specificity in this setting is very high.

	ADVANCES IN KNOWLEDGE

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION ADVANCES IN KNOWLEDGE IMPLICATIONS FOR PATIENT CARE References

 

• Specificity of 100% was achieved in the detection of bile duct narrowing, which is improved when compared to previous reports in which single-detector CT technology was used.
  
• Specificity of 95%–96% was achieved in the detection of choledocholithiasis, which is improved when compared to previous reports in which single-detector CT technology was used.
  
• Sensitivity of 72%–78% was achieved in the detection of choledocholithiasis, which is similar to previous reports in which four- and single-detector CT technology was used.
  

	IMPLICATIONS FOR PATIENT CARE

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION ADVANCES IN KNOWLEDGE IMPLICATIONS FOR PATIENT CARE References

 

• Given the specificity reported in our study for the detection of bile duct narrowing and choledocholithiasis by using portal venous phase imaging with 64-detector CT technology, additional confirmatory imaging may not be necessary.
  
• Given the sensitivities reported in the study for the detection of bile duct narrowing and choledocholithiasis by using portal venous phase imaging with 64-detector CT technology, cholangiography is likely indicated in patients with clinical suspicion of biliary disease.
  

	FOOTNOTES

 

Abbreviations: CI = confidence interval • ERCP = endoscopic retrograde cholangiopancreatography • MRCP = MR cholangiopancreatography

Author contributions: Guarantor of integrity of entire study, S.W.A.; study concepts/study design or data acquisition or data analysis/interpretation, all authors; manuscript drafting or manuscript revision for important intellectual content, all authors; approval of final version of submitted manuscript, all authors; literature research, S.W.A.; clinical studies, S.W.A., E.R.; statistical analysis, S.W.A.; and manuscript editing, S.W.A., E.R.

Authors stated no financial relationship to disclose.

	References

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION ADVANCES IN KNOWLEDGE IMPLICATIONS FOR PATIENT CARE References

 

1. Baron RL, Stanley RJ, Lee JK, et al. A prospective comparison of the evaluation of biliary obstruction using computed tomography and ultrasonography. Radiology 1982;145:91–98.[Abstract/Free Full Text]
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