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1
Department of Radiology, Sasebo Chuo Hospital, 15 Yamato-cho, Sasebo City,
Nagasaki 857-1195, Japan.
2
Department of Radiology, Nagasaki University School of Medicine, Nagasaki,
Japan.
Received August 17, 1999;
accepted after revision January 11, 2000.
Address correspondence to K. Hirao.
Abstract
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SUBJECTS AND METHODS. A total of 120 consecutive patients, including 114 patients with cholecystolithiasis and six with gallbladder polyps, were treated using laparoscopic cholecystectomy between November 1996 and August 1998. Eighteen (15%) of the 120 patients were suspected of having aberrant bile ducts or cystic ducts on helical CT cholangiography, and 16 of these 18 patients were subsequently examined on MR cholangiography. For the 16 patients who underwent both imaging examinations, findings from helical CT cholangiography and MR cholangiography were compared with intraoperative cholangiography.
RESULTS. Aberrant bile ducts in 13 patients and aberrant cystic ducts in three patients were divided into six types on the basis of the results of intraoperative cholangiography. Although these types were clearly identified using helical CT cholangiography in all 16 patients, the anatomic variants were not correctly identified in seven (44%) of the 16 patients with MR cholangiography. False-negative findings were mainly a result of the insertion sites of the cystic ducts or aberrant bile ducts being obscured by aberrant bile ducts or duodenum. Two (2%) of the 120 patients developed mild adverse reactions to the contrast material, but neither required treatment.
CONCLUSION. Helical CT cholangiography clearly showed aberrant bile ducts and cystic ducts, but visualization of these structures on MR cholangiography was unsatisfactory because of overlapping duodenum and hepatic ducts.
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Wallner et al. [7] were the first to report the use of MR cholangiography in 1991. Since then, many investigators have performed MR cholangiopancreatography for detection of bilopancreatic diseases using various imaging sequences [8,9,10,11,12,13]. Greenberg et al. [14] evaluated visualization of the bile ducts using CT with orally administered iopanoic acid. The usefulness of three-dimensional (3D) cholangiography with helical CT for the analysis of bile ducts has been reported [15], and this method has been evaluated by comparing its findings with those of laparoscopic cholecystectomy with regard to the anatomy of the biliary tree [15,16,17]. Although aberrant bile ducts can be detected on either MR cholangiography or helical CT cholangiography [9, 16,17,18,19,20], previous studies have not, to our knowledge, compared the depiction rate of MR cholangiography with that of helical CT cholangiography.
Before the present study began, 67 patients, representing consecutive patients with cholecystolithiasis who were admitted to our hospital between November 1995 and October 1996, were prepared for laparoscopic cholecystectomy. Each patient was routinely examined using helical CT cholangiography for a pilot study. Six patients (9%) were found to have aberrant bile ducts, which were later confirmed by intraoperative cholangiography. In November 1996, we introduced the use of MR cholangiography, in addition to helical CT cholangiography, for patients suspected of having aberrant bile ducts or cystic ducts. The purpose of this study was to compare prospectively the accuracy of helical CT cholangiography with that of MR cholangiography in the diagnosis of aberrant bile duct or cystic duct before laparoscopic cholecystectomy.
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Preoperatively, 18 patients were suspected of having aberrant bile ducts or cystic ducts on the basis of the results of helical CT cholangiography, and 16 of these patients underwent MR cholangiography within 1 or 2 days after helical CT cholangiography. Thus, our study population consisted of 16 patients with aberrant bile ducts or cystic ducts who had undergone both helical CT cholangiography and MR cholangiography.
Helical CT Cholangiography
One hundred milliliters of iotroxate meglumine (Biliscopin; Schering,
Osaka, Japan) was infused IV over a period of 30 min, and helical CT
cholangiography was performed 30 min later. After rolling the patient to mix
bile and contrast material in the gallbladder, helical scans were acquired
with a field of view of 160 mm, a collimation of 3 mm, a table speed of 3
mm/sec, and a matrix of 512x512. Furthermore, the biliary tree was
scanned from the confluence of the bile ducts of segments II, III, and IV
[21] to the papilla of Vater
using a single acquisition. A helical CT scanner (HiSpeed Advantage; General
Electric Medical Systems, Milwaukee, WI) was used, and axial source
two-dimensional (2D) images were reconstructed with a 1.5-mm thickness and
were printed on a laser film. Three-dimensional shaded-surface—display
images were reconstructed using Advantage Windows (General Electric Medical
Systems) with the threshold level between 100 and 130 H. Three-dimensional
shaded-surface—display images were moved on the console, and the
selected views were printed on laser film. Each patient fasted for more than 4
hr before helical CT cholangiography.
MR Cholangiography
MR cholangiography was performed in 16 of the 18 patients suspected of
having aberrant bile ducts or cystic ducts using helical CT cholangiography.
Informed consent for MR cholangiography was obtained from these 16 patients.
The MR examination was conducted using a 1.5-T unit (Gyroscan ACS-II; Philips
Medical Systems, Shelton, CT). Patients fasted for more than 8 hr before MR
cholangiography. Ferric ammonium citrate (FerriSeltz; Ohtsuka Pharmaceuticals,
Tokyo, Japan), an oral contrast material available in Japan since June 1997,
was used in eight consecutive patients. In these patients, the duodenum
overlapped and concealed the biliary system as shown at the time of planning
of scanning planes. MR cholangiography was performed 10 min after patients
drank a mixture of 600 mg of ferric ammonium citrate and 50 mL of water. Four
heavily T2-weighted turbo spinecho sequences with fat-suppression using
spectral presaturation with inversion recovery were performed.
Two respiratory-triggered multislice sequences of MR cholangiography were performed using the quadrature body coil: 2D and 3D T2-weighted turbo spin-echo images were obtained. The scan parameters for the 2D sequence were as follows: TR/TE, 1800/210; echo train length, 21; matrix, 202 x 256; field of view, 250 mm; section thickness, 4 mm; section overlap, 1 mm; number of slices, 20; number of signals acquired, three; average actual scan time, 8 min; and nominal scan time, 216 sec. The scan parameters for the 3D sequence were as follows: 1008/240; echo train length, 31; matrix, 186 x 256; field of view, 250 mm; section thickness, 2 mm; number of slices, 40; number of slabs, four; number of signals acquired, two; average actual scan time, 7 min; and nominal scan time, 191 sec. Patients were instructed to breathe quietly and regularly during the test. Two breath-hold single-shot sequences of MR cholangiography were performed using a 17-cm-diameter ring coil: T2-weighted turbo spin-echo coronal images were obtained without a half-Fourier technique and with a half-Fourier technique. The scan parameters for the first sequence (i.e., without a half-Fourier technique) were the following: 8000/1200; echo train length, 256; matrix, 256 x 256; field of view, 250 mm; single slice of 40-80 mm section thickness; number of signals acquired, one; and total imaging time, 2 sec. The scan parameters for the second sequence (i.e., with a half-Fourier technique) were the following: 3000/320; echo train length, 128; matrix, 217 x 256; field of view, 200 mm; single slice of 10-25 mm section thickness; number of signals acquired, one; and total imaging time, 2 sec. All coronal images obtained using breath-hold MR cholangiography, ranging from -30° to +30° for true coronal images, included the confluence of the cystic duct.
The maximum intensity projections were reconstructed, and two oblique coronal images were displayed from 5° to 7° apart in each scan and were observed stereoscopically. Coronal source images of MR cholangiography were also printed on laser film.
Intraoperative Cholangiography
Intraoperative cholangiography is the standard of reference for this study
and was performed using a 3- to 5-French transcatheter (Cholangiocatheter NU;
Hakko, Tokyo, Japan) injection in the cystic duct of a sufficient volume of
contrast material to identify all the intrahepatic segmental bile ducts. The
fluorography of the intraoperative cholangiography was recorded on
videotape.
Evaluation of Aberrant Bile Ducts and Cystic Ducts
Two experienced radiologists independently reviewed both helical CT
cholangiograms and MR cholangiograms of 16 patients for the diagnosis of
aberrant bile ducts or cystic ducts. They had prior knowledge that patients
had anatomic variants of the bile ducts or cystic ducts. The types of
anomalies and visualization rates of the insertion site of the cystic duct
were first evaluated using both maximum intensity projections and coronal
source images of MR cholangiography and were then evaluated using both
shaded-surface—display and 2D images of helical CT cholangiography; the
order of CT and MR images of the patients was randomly arranged. Finally, we
compared the accuracy of helical CT cholangiography and that of MR
cholangiography in the diagnosis of aberrant bile ducts or cystic ducts. If
there was a discrepancy in the interpretation of the anatomy of the biliary
tree using helical CT cholangiography or MR cholangiography, diagnosis was
made by consensus.
The classification of the aberrant bile ducts and cystic ducts is based on the summation reported by Goor and Ebert [22].
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The presence of aberrant bile ducts or cystic ducts was confirmed on intraoperative cholangiography in 18 (15%) of 118 patients, and 16 of these 18 patients underwent MR cholangiography. Aberrant bile ducts (n = 13) and cystic ducts (n = 3) were divided into six types (Fig. 1A,1B,1C,1D,1E,1F,1G). Type 1 consisted of an aberrant cystic duct draining into an aberrant posterior or anterior bile duct (Fig. 2A,2B). Type 2 consisted of an aberrant posterior bile duct draining into the common hepatic duct immediately above the confluence of the cystic duct (Fig. 3A,3B,3C,3D,3E,3F). Type 3 consisted of an aberrant bile duct draining into the common hepatic duct above the confluence of the cystic duct (Fig. 4A,4B). Type 4 consisted of an aberrant duct draining from the caudate lobe into the common hepatic duct opposite of the confluence of the cystic duct (Fig. 5A,5B); the aberrant bile duct was a posterior duct in nine patients, anterior duct in two patients, anteroinferior branch in one patient, and a caudate branch in one patient. Type 5 consisted of an aberrant cystic duct draining into the right hepatic duct (Fig. 6A,6B); type 6, into the left hepatic duct (Fig. 7A,7B).
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The types of anomaly were correctly diagnosed using 2D helical CT cholangiograms in all the patients; however, in four (25%) of the 16 patients, the types of anomaly were not precisely evaluated using 3D helical CT cholangiograms because the aberrant bile ducts or cystic ducts were small in caliber. The types of anomaly were not well identified in three patients and the aberrant bile duct and cystic duct overlapped in the fourth patient. The draining segments of the aberrant bile ducts were easily evaluated using 2D helical CT cholangiograms. In types 1-3 anomalies, the insertion sites of the cystic duct into the aberrant or common hepatic duct were clearly shown on the posteroanterior 3D shaded-surface—display images, and in type 4 anomalies these insertion sites were shown not only on the posteroanterior but also on the anteroposterior views.
MR cholangiography revealed aberrant bile ducts or cystic ducts in nine of 16 patients, and multislice and single-shot MR cholangiography depicted these anomalies in eight of nine patients. However, in one of the nine patients, neither multislice MR cholangiography nor its coronal source images showed the type of anomaly because of overlapping cystic duct and duodenum, but single-shot MR cholangiography could show the anomaly. The aberrant bile ducts were easily depicted using MR cholangiography in all 13 patients with types 1-4 anomalies, but the insertion sites of aberrant bile ducts and cystic ducts into the common hepatic ducts were identified in only eight (62%) of these patients. The draining segments of the aberrant bile ducts were identified in only seven (54%) of 13 patients on MR cholangiography. The precise classification of all three patients with type 1, of one of two patients with type 2, and of one of seven patients with type 3 was difficult because the insertion site of the cystic duct into the aberrant or common hepatic duct was obscured by overlapping aberrant bile ducts in type 1 and duodenum in types 2 and 3. In one patient, the high signal intensity in the duodenal lumen could not be eliminated completely with the use of oral contrast material, and the insertion site of the cystic duct was not clearly shown. Aberrant cystic ducts were not identified using MR cholangiography in two patients with type 5 anomaly because the ducts were short and close to the gallbladder or because the insertion site of the cystic duct appeared below the confluence of the right and left hepatic ducts of which proximal portions ran parallel with each other.
Diagnosis of aberrant bile ducts types 1-4 was correct in all 13 patients (100%) on helical CT cholangiography and in eight (62%) on MR cholangiography. On the other hand, diagnosis of aberrant cystic ducts of types 5 and 6 was correct in all three patients (100%) on helical CT cholangiography and in one (33%) on MR cholangiography. Thus, the overall diagnostic accuracy of helical CT cholangiography was 100%, whereas that of MR cholangiography was 56%. These rates are similar to the depiction rates of the insertion site of aberrant bile ducts and cystic ducts, respectively.
The types of aberrant bile ducts and cystic ducts were correctly evaluated in six (75%) of eight patients using a high concentration of ferric ammonium citrate and in three (38%) of eight patients not using it. Type 3 anomaly was identified in all three patients (100%) with ferric ammonium citrate and in three (75%) of four patients without it. The other five types of anomalies were correctly classified in three (60%) of five patients with ferric ammonium citrate and in zero of four patients without ferric ammonium citrate.
Two (2%) of 120 patients developed adverse reactions, although neither required treatment. One patient complained of dry cough and the other complained of nausea when 30 mL of the contrast material had been infused for approximately 10 min; both patients recovered soon after discontinuation of the infusion.
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The frequency of identification of the cystic duct or of its insertion site varies according to the pulse sequences of MR cholangiography and ranges from 28% to 93% in patients with biliary diseases [8,9,10,11, 18], and its frequency is 88% in healthy volunteers [12]. Although the cystic duct is delineated in 86-93% of patients using breath-hold sequences, its site of insertion is difficult to identify using breath-hold or non—breath-hold MR cholangiography. Maximum-intensity-projection images obscure the junction of the aberrant bile duct or cystic duct, whereas the coronal source and maximum-intensity-projection images of MR cholangiography cannot sufficiently depict nondilated ducts [8, 18, 27, 28]. In the present study, the types of aberrant bile ducts or cystic ducts could not be evaluated or determined in seven of 16 patients because the insertion site of the cystic duct into the aberrant, right, or common hepatic duct was obscured by overlapping aberrant bile duct or duodenum. In one patient, the type of aberrant bile duct could not be determined because of motion artifacts. Multislice MR cholangiography is susceptible to artifacts caused by movement of the gallbladder or bowels [9, 11, 12].
The mixture of 600 mg ferric ammonium citrate and 50 mL water eliminates the high signal intensity of the duodenum on T2-weighted images and improves the quality of maximum-intensity-projection images of the biliary tree [29]. With the exception of type 3 anomalies, the type of anomaly could not be determined in four patients in whom ferric ammonium citrate had not been used but could be determined in three of five in whom ferric ammonium citrate had been used. Although our results showed the usefulness of high concentrations of ferric ammonium citrate for the evaluation of aberrant bile ducts or cystic ducts, hyperintensity in the duodenal lumen could not be eliminated completely by its use in one patient.
A previous study using 3D helical CT depicted the confluence of the cystic duct and common bile duct in 86% of patients [17]. However, in our study, the insertion site of the aberrant bile duct or cystic duct was correctly identified in all 16 patients with the use of 2D helical CT cholangiographic images. Two-dimensional helical CT cholangiograms delineated small-caliber cystic ducts opacified with the contrast material in all patients. In four of 16 patients, 3D images were not optimal because the aberrant bile ducts were too small to be identified or because the cystic duct was so close to the aberrant bile duct that they overlapped. The liver segments from which an aberrant bile duct or intrahepatic ducts drain can be easily identified using 2D helical CT cholangiograms but not using MR cholangiograms. Two-dimensional helical CT cholangiograms are important to evaluate the biliary anatomy [16, 20].
In contrast to MR cholangiography and helical CT cholangiography, both endoscopic retrograde cholangiography and percutaneous transhepatic cholangiography are invasive operator-dependent techniques and should not be used for the sole purpose of diagnosing biliary diseases such as cholecystolithiasis [10, 15]. Percutaneous transhepatic cholangiography should be performed for subsequent drainage in patients with obstructive jaundice, whereas endoscopic retrograde cholangiography is suitable for endoscopic papillotomy or lithotripsy in patients with suspected choledocholithiasis [30, 31].
The roles of intraoperative cholangiography are different according to institutions; this technique may be performed routinely or may not be performed at all [2, 32,33,34]. Other researchers have advocated performing intraoperative cholangiography selectively in patients suspected of having bile duct stones or anatomic variations [35]. We agree with this guideline, although we routinely performed intraoperative cholangiography in the present study as the gold standard.
The rate of adverse reaction is low when iotroxate meglumine is infused slowly over 20 min [14]. In this study, minor adverse reactions, according to the classification of Ansell and Faux [36], were noted in only two (2%) of 120 patients.
In conclusion, helical CT cholangiography allows clear anatomic delineation of the aberrant bile ducts and cystic ducts.
Acknowledgments
We thank Yukiko Takaki, Ryuji Baba, Toshiharu Kuwamura, Tetsuya Inada,
Seiji Seo, Kazuyuki Harada, and Yasuto Kawakami for their technical support,
and we thank Toshikazu Matsuo, Yoshitaka Taniguchi, Masaaki Jibiki, Kazuhiko
Hatano, Akira Yoshida, Hideki Ikari, Teruhisa Shimizu, Tsunehisa Ishibashi,
Yoji Sugamura, and Tadaomi Kunizaki for their surgical support for this
study.
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