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Original Research |
1 Department of Technical Radiology, Nagoya University School of Health
Sciences, Nagoya, Aichi 461-8673, Japan.
2 Department of Radiology, Nagoya University Graduate School of Medicine,
Nagoya, Aichi, Japan.
Received May 15, 2005;
accepted after revision August 2, 2005.
Address correspondence to S. Itoh
(shigeito{at}met.nagoya-u.ac.jp).
Abstract
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MATERIALS AND METHODS. This study included nine patients with and 54 without an anomalous pancreaticobiliary ductal junction confirmed on direct cholangiopancreatography. Multiplanar reconstruction images with 0.5-mm continuous slices were generated from isotropic or nearly isotropic pancreatic phase images. By mainly interpreting the multiplanar reconstruction images using the Scrolling mode, two blinded reviewers independently determined whether the confluence of the pancreatic and biliary ducts joined in the pancreatic parenchyma (in other words, outside the duodenal wall). The results were correlated with the findings of direct cholangiopancreatography. The diagnostic capabilities of CT for revealing associated pancreatobiliary diseases were assessed in patients with this anomaly.
RESULTS. Interobserver agreement in the classification of the duct
confluence was high (
= 0.804). The duct confluence was identified in
all patients except four without an anomalous pancreaticobiliary ductal
junction. The sensitivity, specificity, accuracy, positive predictive value,
and negative predictive value of CT for diagnosing an anomalous
pancreaticobiliary ductal junction were 100% (9 of 9 patients), 87% (47 of 54
patients), 89% (56 of 63 patients), 75% (9 of 12 patients), and 100% (47 of 47
patients) in the final decisions, respectively. CT showed all associated
pancreatobiliary diseases except bile duct stones in two patients.
CONCLUSION. MDCT enabled the diagnosis of an anomalous pancreaticobiliary ductal junction by showing whether the pancreatic and biliary ducts join within the pancreatic parenchyma on high-resolution multiplanar reconstruction images.
Keywords: bile ducts • CT technology • dynamic CT • MDCT • pancreaticobiliary ductal junction • pancreatic ducts
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ERCP is the most reliable method for depicting an anomalous pancreaticobiliary ductal junction, but it is an invasive procedure. Previous studies have shown that endoscopic sonography and MR cholangiopancreatography (MRCP) are also useful for the diagnosis of this anomaly [5-8]. When ERCP is used as the reference standard, the detectability rates of endoscopic sonography and MRCP for this anomaly have been reported to be 88% and 82%, respectively [5, 6]. However, to our knowledge, the capabilities of CT for the diagnosis of this anomaly have not been evaluated in any study except one case report [9].
Recent advances in helical CT technology, such as multidetector and subsecond rotation, have made it possible to scan the pancreas and biliary system with a collimation of 1.25 mm and less. This results in further improvement in the quality of multiplanar reformatted (multiplanar reconstruction) images due to the superior resolution in the z-axis, and multiplanar reconstruction images allow us to select the optimal sectional planes for evaluation of the pancreatic and bile ducts and their confluence. The present study was therefore conducted to assess the capabilities of MDCT for allowing the diagnosis of an anomalous pancreaticobiliary ductal junction using multiplanar reconstruction images generated from pancreatic phase images with a 0.5- or 1-mm slice thickness.
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We retrospectively reviewed the charts of patients during the study period and identified 84 patients who had undergone both of the appropriate CT examinations using these protocols and ERCP examinations (n = 77) or intraoperative cholangiopancreatography examinations (n = 7) and had opacification of all of the common bile duct, main pancreatic duct, and common channel. We excluded 21 patients who had tumors of the pancreatic head because we thought that the tumor would hinder the evaluation for the confluences of the pancreatic and biliary ducts on CT images. Thus, the study group comprised 63 patients (33 women and 30 men; age range, 24-81 years; mean age, 61 years). The study was performed in accordance with the routine clinical standards of our institution, and written informed consent for CT and ERCP examinations was obtained from each patient after the purpose and methods of the examinations were fully explained. Our institutional review board approved retrospective data collection and analysis for this research, with waived informed patient consent.
Direct cholangiopancreatography was performed and assessed by experienced physicians or surgeons at our institution, and cases in which the common channel was 15 mm or longer on direct cholangiopancreatography were diagnosed as an anomalous pancreaticobiliary ductal junction [3]. Based on these results, nine patients (six women and three men; age range, 24-67 years; mean age, 52 years) had this anomaly (Table 1). Of these patients, five had congenital choledochal cyst and four showed no evidence of congenital choledochal cyst on ERCP and pathologic examinations. Surgical and pathologic examinations showed associated pancreatobiliary diseases in all patients except one. On the other hand, 54 patients (27 women and 27 men; age range, 28-81 years; mean age, 63 years) had a normal pancreaticobiliary ductal junction. The patient with choledochocele (type III of the classification of Todani et al. [10]) did not have an anomalous pancreaticobiliary ductal junction. Eight patients underwent percutaneous transhepatic or endoscopic retrograde biliary drainage before the CT examinations.
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CT Image Acquisition
Five minutes before undergoing CT, the patient was instructed to drink 300
mL of water for negative opacification of the gastrointestinal tract. Nonionic
contrast material with an iodine concentration of 300 mg I/mL was injected at
0.08 mL/kg of body weight per second over 30 seconds, and a 5% dextrose flush
was administered at a fixed rate of 5 mL/s over 6 seconds immediately after
the end of the injection of contrast material. The injection of both contrast
material and 5% dextrose was performed using two automatic power injectors
(Auto Enhance A50 and Auto Injector 1205, Nemotokyorindo) via a 20-gauge IV
catheter placed in an antecubital vein.
In the 23 patients who underwent three-phase contrast-enhanced CT studies, arterial and pancreatic phase images were obtained with a detector-row configuration of 4 x 1 mm and a table increment of 5.5 mm/rotation during a single breath-hold. In the 40 patients who underwent dual-phase contrast-enhanced CT studies, pancreatic phase scanning was performed with a detector-row configuration of 4 x 0.5 mm and a table increment of 2.75 mm/rotation. These images were acquired from the porta hepatis to the end of the duodenum. The other scanning parameters were constant in both protocols (Tables 2 and 3).
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For the three-phase contrast-enhanced CT studies of patients more than 60 years old or who had cardiovascular disease (or both), arterial phase scanning was started as soon as possible (9 seconds on average) after the attenuation values in the aorta at the same level as the start position of scanning reached a value of 80 H or higher using the automatic bolustracking method (SureStart, Toshiba). In the other patients, the scan delay from the administration of contrast material to the start of arterial phase scanning was set at 24 seconds. For dual-phase contrast-enhanced CT studies of patients more than 60 years old or who had cardiovascular disease (or both), pancreatic phase scanning was started at 11 seconds after the attenuation value in the aorta reached 130 H or higher using the automatic bolus-tracking method. In the other patients, the scan delay from the administration of contrast material to the start of arterial phase scanning was set at 30 seconds. The time interval between the pancreatic and portal phases was fixed at 15 seconds.
Image Processing and Analysis
Pancreatic phase images were reconstructed with a 0.5-mm slice thickness at
0.5-mm intervals and with a 1-mm slice thickness at 0.5-mm intervals,
respectively, using a 260-mm field of view, and were transferred to an image
workstation (Alatoview, Toshiba). One radiologist reconstructed the
multiplanar reconstruction images with a 0.5-mm slice thickness at 0.5-mm
intervals to cover the pancreatic parenchyma. Then, an average of
approximately 60 sections were obtained in each patient. The oblique angles
for the multiplanar reconstruction images were selected to visualize the
confluence of the pancreatic and biliary ducts most clearly by using
interactive oblique views. Thus, left anterior oblique sections were used in
most patients.
Two radiologists with 20 and 6 years' experience interpreting abdominal CT examinations who were blinded to other imaging, surgical, and pathologic findings independently interpreted the images using the Scrolling mode. First, the reviewers assessed the multiplanar reconstruction images. When evaluation of the confluence of the pancreatic and biliary ducts on the multiplanar reconstruction images alone was judged to be insufficient, the axial source images were evaluated conjointly.
On the basis of the relationship between the duct confluence and the pancreatic parenchyma showing intense contrast enhancement, each patient was grouped into one of the following three types: type 1, the pancreatic and biliary ducts join within the pancreatic parenchyma (Fig. 1); type 2, the pancreatic and biliary ducts follow independent courses within the pancreatic parenchyma (in other words, the pancreatic and biliary ducts do not join within the pancreatic parenchyma) (Fig. 2); or type 3, the relationship between the duct confluence and the pancreatic parenchyma cannot be determined. Results from each reviewer were compared with the kappa statistic to measure interobserver agreement in the classification of the duct confluence. In cases of interobserver disagreement, the final decisions were reached by consensus. In this study, patients with findings classified as type 1 were judged to have an anomalous pancreaticobiliary ductal junction on CT.
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We correlated the results of CT with those of direct cholangiopancreatography used as the reference standard in terms of the presence or absence of an anomalous pancreaticobiliary ductal junction in all patients. In patients with an anomalous pancreatobiliary ductal junction, a discrepancy between CT and direct cholangiopancreatography, or both, the findings of CT relating to the configuration of the pancreatobiliary tract and associated pancreatic and biliary diseases were compared with those of imaging, surgical, and pathologic examinations.
In the interpretation of the multiplanar reconstruction images, we noticed that an area showing less contrast enhancement was visible between the pancreatic head and the duodenum in many cases, and this area exhibited a variety of shapes, such as fanlike, bandlike, and linear shapes (Figs. 1 and 2). One reviewer therefore assessed the presence of this area according to the following 3-grade scale in all patients: 1, clearly depicted; 2, probably depicted; and 3, not depicted. Furthermore, while paying attention to the relationship between the confluence of the pancreatic and biliary ducts and the area showing less contrast enhancement, reevaluation combined with the findings of direct cholangiopancreatography was performed in the cases classified as type 1.
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Thus, when direct cholangiopancreatography was used as the reference standard, the sensitivity, specificity, accuracy, positive predictive value, and negative predictive value of CT for diagnosis of an anomalous pancreaticobiliary ductal junction were 100% (9 of 9 patients), 87% (47 of 54 patients), 89% (56 of 63 patients), 75% (9 of 12 patients), and 100% (47 of 47 patients) in the final decisions, respectively.
Of the nine patients with an anomalous pancreatobiliary junction, the findings of CT images relating to the configuration of the pancreatobiliary tract were in agreement with those of direct cholangiopancreatography for all nine patients (Figs. 4A and 4B). Of the associated pancreatobiliary diseases proved by surgical and pathologic examinations, CT revealed congenital choledochal cyst (n = 5), bile duct carcinoma (n = 3), adenomyomatosis of the gallbladder (n = 2), cholecystitis (n = 2), and gallbladder carcinoma (n = 1). However, in two patients with bile duct stones with cholecystitis, CT showed thickening of the gallbladder wall but the reviewer did not detect the stone. The maximum diameter of the congenital choledochal cyst measured between 12.4 and 26.3 mm (mean ± SD, 20.0 ± 6.7 mm) on CT (Table 1).
Visualization of the area showing less contrast enhancement between the pancreatic head and the duodenum on the multiplanar reconstruction images was graded as clearly depicted for 42 patients (67%), as probably depicted for 14 (22%), and as not depicted for seven (11%), respectively. Excluding five patients in whom artifacts due to the presence of biliary drainage tubes prevented visualization of the area, only two patients were assigned a grade of "not depicted" (Table 4). In the patients with findings classified as type 1, reevaluation combined with the findings of direct cholangiopancreatography revealed that, in three patients without an anomalous pancreaticobiliary ductal junction, the pancreatic and biliary ducts joined in the portion of the ducts that involved less contrast enhancement (Figs. 5A and 5B); on the other hand, in nine patients with this anomaly, these ducts showing water attenuation joined within the pancreatic parenchyma (Figs. 1, 3A, 3B, 4A, and 4B).
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Alternatively, MDCT made it possible to determine the relationship between the confluence of the pancreatic and biliary ducts and the pancreatic parenchyma in all patients except four, and in 52 patients, the relationship could be clearly identified on the basis of findings of multiplanar reconstruction images alone. The following reasons may account for these favorable results. First, isotropic or nearly isotropic imaging using axial reconstruction images with a 0.5- or 1-mm slice thickness at 0.5-mm intervals over a 260-mm field of view provides sufficiently high resolution in the z-axis for the evaluation of the pancreatic and biliary ducts [11]. Second, because the bile duct passes obliquely through the pancreatic head and the second part of the duodenum and joins the pancreatic duct to form the ampulla of Vater [12], multiplanar reconstruction images are suitable for evaluating the appearance of the duct confluence. Third, based on the results of previous studies [13], we scanned the pancreas to acquire pancreatic phase images 40-50 sec, on average, after the administration of contrast material. This protocol makes it possible to achieve intense contrast enhancement of the pancreatic parenchyma, which improves the conspicuity of the pancreatic and biliary ducts.
In the present study, with the use of multiplanar reconstruction images, MDCT was able to show that the pancreatic and biliary ducts joined within the pancreatic parenchyma (in other words, outside the duodenal wall) in all nine patients with an anomalous pancreaticobiliary ductal junction, whereas these ducts followed independent courses within the pancreatic parenchyma in 47 (87%) of 54 patients with a normal pancreaticobiliary ductal junction. These results indicate that with the use of high-resolution multiplanar reconstruction images, MDCT allows us to diagnose an anomalous pancreaticobiliary ductal junction on the basis of findings regarding the relationship between the duct confluence and the pancreatic parenchyma.
In this study, multiplanar reconstruction images permitted an area showing less contrast enhancement between the pancreatic head and the duodenum to be visualized in 89% (56 of 63) of the patients. Furthermore, reevaluation in 12 patients in whom the duct confluence was located within the pancreatic parenchyma revealed that in three patients with a normal pancreaticobiliary ductal junction the pancreatic and biliary ducts joined in the portion of the ducts involved in the area that showed less contrast enhancement, whereas these ducts joined proximal to that area in the nine patients with an anomalous pancreaticobiliary ductal junction.
Anatomically, the biliary and pancreatic ducts near the ampulla of Vater are formed by a thickening of both the longitudinal and circular layers of smooth muscle of the sphincter of Oddi. This structure is composed of the following parts: the common bile duct sphincter, which surrounds the distal portions of the common bile duct before its junction with the pancreatic ducts; the pancreatic duct sphincter, which is present in approximately one third of individuals and surrounds the distal portions of the pancreatic ducts before its junction with the ampulla of Vater; the fasciculi longitudinales, which spans intervals between the biliary and pancreatic ducts; and the sphincter of ampulla, which surrounds the common channel [4, 12]. Functionally, the sphincter of Oddi prevents the reflux of pancreatic juice into the biliary duct or the reflux of bile into the pancreatic duct. In persons with an anomalous pancreaticobiliary ductal junction, because the confluence of the pancreatic and biliary ducts is located in the portion of the ducts not surrounded by muscular sphincters, the pancreatic juice flows into the biliary duct. This results in injury to the epithelium of the biliary tract, which may ultimately lead to the development of malignancies [3, 4].
If it is hypothesized that the area showing less contrast enhancement between the pancreatic head and the duodenum on multiplanar reconstruction images corresponds to the area of the ducts surrounded by muscular sphincters associated with the surrounding connective tissues, the anatomic and pathophysiologic findings mentioned can be applied to the CT findings of the present study. Furthermore, the results of this study suggest that CT diagnosis of this anomaly may be improved by paying attention to this area showing less contrast enhancement. Further studies are needed to establish the histopathologic basis for this area visualized on multiplanar reconstruction images and to evaluate its value for the diagnosis of this anomaly.
There are some limitations in the present study. Because only the CT images of the patients undergoing direct cholangiopancreatography were retrospectively reviewed, the number of patients was relatively small, and there might be bias regarding the selection of patients and frequency of CT findings. A comparison of multiplanar reconstruction images and axial images was not performed in this study. However, researchers of previous studies have reported that multiplanar reconstruction images significantly improve the depiction of the pancreatic and biliary ducts and their confluences in comparison with axial images [11, 14], and it takes only a few minutes to generate the images and evaluate the duct confluence.
In previous studies, researchers reported that multiplanar reconstruction images using minimal intensity projection or volume rendering provide adequate information about the pancreatic and bile ducts [15]. Because generating comparable images was not possible due to the capabilities of the workstation used, we could not directly compare these techniques with that used in the present study. Although multiplanar reconstruction images using these techniques may provide a global view of the pancreaticobiliary ductal junction, the image processing used in this study requires less skill and is less time consuming and the images obtained are not affected by degradation in both contrast resolution and sharpness due to the thickness of the tissue slabs. Further prospective studies are needed to clarify the diagnostic capabilities of axial images, these multiplanar reconstruction images, and both axial and multiplanar reconstruction images in combination for detecting this anomaly to determine the most suitable clinical applications of these images.
In comparison with MRCP and endoscopic sonography, CT suffers from the drawback that both radiation exposure and the injection of contrast material are required. However, CT is the most commonly used imaging technique for the evaluation of pancreatic and biliary diseases. An anomalous pancreaticobiliary ductal junction is frequently associated with not only carcinoma of the biliary tract but also various pathologic conditions in the pancreatobiliary region such as dilatation of the bile duct, wall thickening or polypoid lesions of the gallbladder, and acute pancreatitis of unknown cause [2-7, 10]. Furthermore, the treatment of choice for patients with these pathologic conditions is strongly influenced by the presence or absence of this anomaly [2, 10]. Therefore, the findings of the present study are important when performing CT of the pancreas and biliary system using an MDCT scanner.
In conclusion, the use of multiplanar reconstruction images generated from pancreatic phase images with a slice thickness of 0.5 or 1 mm allowed us to diagnose cases of anomalous pancreaticobiliary ductal junction by showing whether the pancreatic and biliary ducts join within the pancreatic parenchyma.
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