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1
Department of Diagnostic Radiology, Research Institute of Radiological
Science, Yonsei University College of Medicine, Seodaemun-ku Shinchon-dong
134, Seoul 120-752, Republic of Korea.
2
Brain Korea 21 Project for Medical Science, Yonsei University College of
Medicine, Seoul 120-752, Republic of Korea.
3
Division of Gastroenterology, Department of Internal Medicine, Yonsei
University College of Medicine, Seoul 120-752, Republic of Korea.
Received May 23, 2001;
accepted after revision October 19, 2001.
Address correspondence to M.-J. Kim.
Abstract
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SUBJECTS AND METHODS. Fifty patients with suspected pancreaticobiliary disorders were separated into three groups. Group I patients had biliary dilatation with periampullary lesions (n = 16), group II patients had supraampullary obstructive lesions (n = 17), and group III patients had biliary dilatation without obstruction (n = 17). Twenty consecutive single thick-slice MRCP images were obtained in the 15° or 30° left anterior oblique coronal plane. Two radiologists jointly reviewed the images without knowledge of the final diagnosis. The numbers of images showing relaxation of the sphincteric segment and the configuration of the distal margin of the common bile duct for the three groups were compared.
RESULTS. Relaxation of the sphincteric segment was observed on the images of only two patients (12%) in group I but on the images of all patients in groups II and III, although not on all images. Lack of visualization of sphincteric relaxation on the kinematic MRCP images had a sensitivity of 88% and a specificity of 100% for the diagnosis of periampullary lesions. Most patients whose images did not show sphincteric relaxation required biliary intervention at the sphincter level.
CONCLUSION. Nonvisualization of sphincteric relaxation on kinematic MRCP indicates ampullary or periampullary lesions. Kinematic MRCP can be used to determine the necessity of biliary intervention in patients with biliary dilatation.
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With the single-shot half-Fourier rapid acquisition and relaxation enhancement technique, a single thick-slice MRCP image can be obtained in 2-3 sec. Therefore, this technique allows the acquisition of serial MRCP images so that the dynamic changes of the sphincteric segment of the pancreaticobiliary junction may be evaluated [8,9,10]. Van Hoe et al. [10] obtained serial breath-hold MRCP images using a single-shot technique in patients with normal Vaterian sphincter complex and showed the usefulness of this method in the evaluation of the distal portion of the common bile duct. These researchers found that in using this technique, nonvisualization of the sphincteric segment (caused by physiologic contraction of the Vaterian sphincter) may be distinguished from pathologic stenosis. However, to our knowledge, no results have been published concerning the efficacy of this technique for the evaluation of the pathologic condition.
In our study, we evaluated patients with biliary dilatation using multiple single-shot thick-slice MRCP images that were serially acquired in a single plane. We call this technique "kinematic MRCP" to emphasize its ability to capture the motion changes of the sphincteric segment. This technique may also be called "dynamic MRCP." We avoid using this term so that the technique will not be confused with dynamic perfusion imaging performed with IV contrast media. We undertook the study to evaluate whether kinematic MRCP images could aid one in detecting the presence of periampullary lesions and predicting the necessity for biliary intervention in patients with biliary dilatation.
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Patients were divided into three groups on the basis of the final diagnosis. Group I consisted of 16 patients with periampullary obstructive lesions—six patients with periampullary carcinomas (two with ampullary carcinomas, two with distal bile duct carcinomas, and two with pancreatic carcinomas) and ten patients with benign ampullary stenosis. All the malignant lesions were confirmed by surgery or biopsy. Of the ten patients with benign ampullary stenosis, four had associated choledocholithiasis. Stone-induced ampullary stenosis was considered the cause of bile duct dilatation in these four patients. Stone removal after endoscopic sphincterotomy was attempted in all and was successful in three patients. In the one failed endoscopic sphincterotomy, an open cholecystectomy with common bile duct exploration was performed. In four patients, pancreatitis was considered the cause of the ampullary obstruction. The patients' biochemical profiles of jaundice resolved after an improvement in their pancreatitis; one of these patients underwent endoscopic sphincterotomy. In the remaining two patients, previous choledocholithiasis was believed to have caused the ampullary stenosis because the patients' liver enzyme levels returned to normal during the admission period before the cholecystectomy for calculous cholecystitis. Endoscopic sphincterotomy was performed in one of the two patients.
Group II consisted of 17 patients with supraampullary lesions who showed evidence of biliary obstruction, but the obstructive lesion did not involve the sphincteric segment. This group included four patients with hilar cholangiocarcinoma, 10 patients with choledocholithiasis in which calculi were floating in the common bile duct lumen, and three patients with a benign stricture in the common bile duct. In the three patients with benign strictures of the common bile duct, the benign stricture was thought to be a postsurgical complication from a previous cholecystectomy in one and pancreatitis in the remaining two. This observation was in accordance with their clinical histories and laboratory findings, and it correlated with the findings of other imaging modalities.
Group III consisted of 17 patients with biliary dilatation without obstruction—two patients with postcholecystectomy syndrome, three patients with recurrent pyogenic cholangitis, five patients with calculous cholecystitis with dilatation of the common bile duct, and seven patients with biliary dilatation of unknown cause. Dilatation of the biliary tree associated with calculous cholecystitis in the absence of an obstructive lesion was diagnosed in patients who showed no evidence of ampullary stenosis or choledocholithiasis on endoscopic retrograde cholangiopancreatography and who had normal laboratory findings after cholecystectomy as well as an absence of signs of bile duct obstruction during a follow-up period of at least 6 months. Cases of postcholecystectomy syndrome or biliary dilatation of unknown cause were diagnosed on the basis of the absence of an obstructive lesion on sonography, CT, endoscopic retrograde cholangiopancreatography (n = 2), or MRCP and an absence of symptoms or signs of biliary obstruction during a follow-up period of at least 6 months.
Imaging Techniques
MR imaging was performed on a 1.5-T unit (Horizon; General Electric Medical
Systems, Milwaukee, WI) with a phased array body coil. No antispasmodic
medication or oral or IV contrast media was given. Initially, the biliary
tract and pancreatic duct were localized with a half-Fourier rapid acquisition
and relaxation enhancement sequence (single-shot fast spin-echo) in the
coronal and axial planes. Thick-slice MRCP images were then obtained in the
coronal and sagittal planes and in the 15°, 30°, and 45° left and
right oblique planes. From these images, an optimal plane for the
visualization of the sphincteric segment was determined. Usually this optimal
plane was the 15° or 30° left anterior oblique coronal plane. Finally,
20 consecutive single thick-slice kinematic MRCP images were obtained using a
breath-hold single-shot fast spin-echo sequence in the predetermined optimal
plane. Each image was obtained during a single breath-hold of 2-3 sec at the
end of expiration. Parameters were TE range, 800-1200; received bandwidth, 31
kHz; reconstructed field of view, 20 x 20 cm; matrix size, 256 x
256; and slice thickness, 30 mm.
Image Analysis and Statistics
Two radiologists reviewed hard-copy images in conference without any
knowledge of the results of other imaging studies, clinical or laboratory
data, or the final diagnosis. The cinematic display of the kinematic MRCP
images was reviewed on a monitor using Digital Imaging Communications In
Medicine image-viewing software (
-view, v3.XX; Mediface, Seoul,
Korea).
The reviewers determined the gross shape (tapered, blunted, papillary, meniscoid, or bird's beak) of the distal margin of the common bile duct in each image of the kinematic MRCP (Fig. 1) and recorded the number of shapes depicted in each patient and the number of the images depicting the relaxation of the sphincteric segments. The sphincteric segment was defined as relaxed if the continuation of the common bile duct to the duodenal lumen was depicted in at least one of the kinematic MRCP images. The sphincteric segment was defined on the kinematic MRCP to be the common channel of the common bile duct and pancreatic duct if the pancreaticobiliary union was visible on the MRCP images or as the gradually narrowing, approximately 1-cm-long segment of the distal margin of the common bile duct if the pancreaticobiliary junction was not seen on the MRCP images.
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One-way analysis of variance was used to compare the differences in the numbers of patients and images depicting the relaxation of the sphincteric segment among the three groups. The analysis of variance test was also used to compare the incidence of visualization of each type of shape of the distal common bile duct among the groups. Differences in which p was less than 0.05 were considered statistically significant.
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Of the 14 patients who did not show sphincteric relaxation on kinematic MRCP, 12 underwent attempts at biliary intervention— percutaneous biliary drainage in five, endoscopic stent insertion in three, and endoscopic sphincterotomy in four. Regression of biliary dilatation was noted in the remaining two patients who received conservative management. Of the two patients that showed sphincteric relaxation on the kinematic MRCP, the patient with ampullary carcinoma underwent pancreaticoduodenectomy without preoperative intervention. In the other patient, endoscopic stone removal failed, and open cholecystectomy with common bile duct exploration was performed. All of the group II patients required percutaneous or endoscopic biliary drainage or stent insertion to relieve obstructive jaundice. In some patients, these were the only procedures required; in others, these procedures were done preoperatively. Among group II patients, biliary intervention was performed above the obstructive lesion, and sphincterotomy was not required. None of the group III patients underwent biliary intervention to relieve biliary dilatation.
Thirty patients (60%) showed more than two shapes of distal margin of the common bile duct on the kinematic MRCP images (Fig. 1). A tapered shape was most common and was observed in 33 patients (66%). This shape was followed in order of frequency by the blunted, papillary, meniscoid, and bird's beak forms (46%, 24%, 14%, and 14%, respectively) (Table 2). The bird's beak shape was significantly (p < 0.05) more common in group I (n = 6; four of the malignant cases and two of the benign cases). However, the other shapes were not correlated with individual groups. The number of common bile duct shapes depicted on the kinematic MRCP was not significantly different in the three groups. Eleven patients (69%) of group I, 14 patients (82%) of group II, and 15 patients (88%) of group III showed more than two shapes of the distal margin of the common bile duct. In the 14 patients of group I that did not show relaxation of the distal common bile duct on any of the kinematic MRCP images, nine (64%) showed changes in the shape of the common bile duct's distal margin (Fig. 6A,6B,6C,6D).
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The acquisition of serial MRCP images to evaluate the dynamic changes of the sphincteric segment was initially described by Matos et al. [9], and the technique has been used to examine the morphology and contractility of the sphincteric segment [10], assess the pancreatic exocrine function [14,15,16,17], and reveal the anomalous pancreaticobiliary duct union in choledochal cysts [18].
Van Hoe et al. [10] described the usefulness of kinematic MRCP for the evaluation of the morphology and contractility of the normal sphincteric segment. The researchers showed that the nonvisualization of the sphincteric segment on conventional MRCP can be a normal finding and that sphincteric motility could be visualized in most healthy patients (97%) on serial breath-hold images. Although patients with subclinical indicators might have been included in their study, Van Hoe et al. believed their technique to be helpful in eliminating false-positive or false-negative diagnoses in patients with periampullary disease. Our study supports these findings.
In our study, sphincteric relaxation was observed in all patients with nonperiampullary lesions, but in only two of 16 patients with periampullary lesions. Thus, nonvisualization of sphincteric relaxation on kinematic MRCP implies the presence of a periampullary obstruction. The modality has a sensitivity of 88% and a specificity of 100% in regard to this condition. The two patients with periampullary lesions showed some relaxation of the sphincteric segment. In the patient with ampullary carcinoma, some relaxation of the sphincteric segment was observed on several images, although the degree of the relaxation seemed incomplete compared with the adjacent common bile duct (Fig. 4A,4B). In the patient with an impacted stone in the distal common bile duct, a thin channel of sphincteric segment was seen on two kinematic MRCP images, but the impacted stone was obvious and partially obscured the sphincteric segment. Therefore, careful analysis of the degree of the relaxation and the shape of the sphincteric segment on the kinematic MRCP image as well as comparison with both other static MRCP images obtained at different angles and conventional MR images proved helpful in determining the correct diagnosis.
Our study shows that kinematic MRCP provides information helpful in deciding whether biliary dilatation requires intervention. Among our patients, sphincteric relaxation was depicted in all group III patients, and none of these patients underwent biliary intervention at the level of the sphincter unless further bile duct obstruction indicators developed. Most patients in groups I and II underwent appropriate biliary intervention, such as sphincterotomy or percutaneous or endoscopic biliary drainage procedures. In the one patient with an ampullary carcinoma who showed sphincteric relaxation on kinematic MRCP, signs of bile duct obstruction were mild so biliary intervention was not required before surgery for the primary lesion.
Among the patients with nonperiampullary lesions who showed sphincteric relaxation, the patients with a supraampullary obstruction (group II) had a greater number of sphincteric relaxation images than those without such an obstruction (group III). The reason for this finding is unknown, but the hormonal activity of cholecystokinin may explain the phenomenon. As diminished bile excretion stimulates the secretion of cholecystokinin or induces the up-regulation of cholecystokinin receptors that are distributed in the smooth muscle of the gallbladder and sphincter of Oddi, the gallbladder contracts and empties and the Oddi sphincter relaxes [12, 13]. This mechanism may explain why patients with supraampullary biliary obstruction show much more sphincteric relaxation on kinematic MRCP.
The shape of the end of the common bile duct was found to be both diverse and dynamic during the serial acquisition of the kinematic MRCP images. Although the bird's beak shape of the distal margin of the common bile duct was significantly more common in group I, the shape was also observed in patients with both benign and malignant lesions. Moreover, the other shapes did not correlate with the presence or absence of biliary obstruction. Therefore, the morphologic appearance of the distal margin of the common bile duct cannot be used as the sole criterion for the differentiation of the various biliary and periampullary diseases.
We believe that the changing shape of the distal ends of the common bile duct may suggest preserved contractility, regardless of the presence of periampullary obstruction. The shape of the end of the common bile duct is not necessarily associated with the level of obstruction or disease. In the periampullary lesions, nine of 14 patients who did not show sphincteric relaxation also displayed more than two configurations of the distal common bile duct, suggesting that lack of visualization of the sphincteric relaxation on the kinematic MRCP does not mean that contractility of the bile duct is impaired and that the nonvisualization may be induced by mechanical or functional abnormalities of parts of the sphincter or of the periampullary portion, regardless of preserved bile duct contractility.
Our study has limitations that should be mentioned. First, we did not compare the relative diagnostic value or accuracy of kinematic MRCP with conventional MRCP in terms of the differentiation of periampullary lesions. The clinical value of the kinematic MRCP technique for the differentiation of periampullary lesions should be further evaluated in a larger number of patients. Second, kinematic MRCP provides serial consecutive images rather than real-time images, but our study shows that kinematic MRCP images could be effectively used in the evaluation of the contractility and relaxation characteristics of the sphincteric segments. Use of the modality in such a way would be similar to the use of cardiac MR imaging, in which consecutive images obtained at close and regular intervals are used to evaluate physiologic function of the heart. Kinematic MRCP can be performed without any preparation or drug administration. MR pancreatography has been performed after secretin stimulation by other researchers who evaluated the morphologic and functional changes of the pancreatic duct [9, 14,15,16,17,18]. Secretin could be useful in delineating the pancreatic duct but may not be useful in depicting the bile duct. Kinematic MRCP after the ingestion of a fatty meal or cholecystokinin may induce transient biliary dilatation that would also be useful in reducing the number of false-negatives and false-positives. Further studies are needed to confirm this hypothesis.
In conclusion, our results show that nonvisualization of sphincteric relaxation on kinematic MRCP indicates ampullary or periampullary lesions. Sphincteric relaxation was visualized in all patients without periampullary disease who did not require biliary intervention, whereas the lack of visualization of the sphincteric segment was found to be indicative of periampullary disease and the need for biliary intervention at the level of the sphincter. Kinematic MRCP can be used to determine the necessity of therapeutic intervention in a patient with biliary dilatation.
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