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Pediatric Imaging |
1 From the Departments of Radiology (K.I.N., R.B.G., J.S.L.), Pediatrics (K.I.N., D.K., B.L.S.), and Surgery (S.E., B.L.S.), and the Recanati/Miller Transplantation Institute (S.E.), Mount Sinai School of Medicine, 1 Gustave L Levy Pl, Box 1234, New York, NY 10029. Received May 25, 2001; revision requested June 26; revision received July 26; accepted September 7. Address correspondence to K.I.N. (e-mail: karen.norton@msnyuhealth.org).
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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MATERIALS AND METHODS: Twenty-six infants (15 male, 11 female; median age, 2 months) underwent MR cholangiography with a 1.5-T MR imaging unit. Original interpretations were compared with clinical outcome. Statistical analysis was performed to determine the accuracy of MR cholangiography in depicting extrahepatic biliary atresia. Equivocal cases and any cases lost to follow-up were excluded.
RESULTS: Findings in six of 26 infants were interpreted as normal, and none of five patients (one lost to follow-up) had biliary atresia or other surgical lesions; two were abnormal but not suggestive of biliary atresia (one false-negative finding); 12 were consistent with biliary atresia (three false-positive findings); four demonstrated a choledochal cyst; and two were equivocal. MR cholangiography accuracy was 82% (19 of 23); sensitivity, 90% (nine of 10); and specificity, 77% (10 of 13) for the detection of extrahepatic biliary atresia, with a positive predictive value of 75% (nine of 12) and a negative predictive value of 91% (10 of 11).
CONCLUSION: Results of this study found that MR cholangiography is 82% accurate, 90% sensitive, and 77% specific for depicting extrahepatic biliary atresia. Contrary to previous reports, false-positive and false-negative findings occur at MR cholangiography.
© RSNA, 2002
Index terms: Bile ducts, abnormalities, 76.1434 • Bile ducts, MR, 76.121411, 76.121416, 76.12142, 76.12143 • Infants, gastrointestinal tract, 76.1434 • Infants, newborn, gastrointestinal tract, 76.1434
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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All MR studies were performed after sedation with 75–100 mg per kilogram of body weight of chloral hydrate administered orally. No secretin or other pharmacologic agent to stimulate secretin was administered before treatment. Studies were performed with a 1.5-T MR imaging unit (Horizon or Signa; GE Medical Systems, Milwaukee, Wis) by using a quadrature head coil or a cardiac body coil. Images were obtained in both axial and coronal planes. Source images and three-dimensional reconstructions obtained with a maximum intensity projection algorithm were analyzed by one of two pediatric radiologists (including K.I.N.), who were not blinded to the clinical information.
Several techniques were used, including thin-section (3 mm thick with no intersection gap) single-shot imaging, thick-slab (5 cm) technique, and thin-collimation (2–3 mm with no intersection gap) multisection fat-saturated respiratory-triggered fast spin-echo technique. Imaging times ranged from 2 seconds for the single-shot technique to between 4 and 12 minutes per acquisition for the respiratory-triggered study, in which the repetition time was determined by the respiratory rate, which ranged between 3,750 and 15,000 msec (average, 
10,000 msec). The effective echo time was 256 msec. Flow compensation and an echo-train length of 16 were used. For thin-section single-shot examinations, an infinite repetition time, an effective echo time of approximately 185 msec, echo-train length of 128, and reconstruction after half of the phase-encoding steps (0.5 signal acquired) shortened the acquisition times. In thick-slab studies, an infinite repetition time, effective echo time of 600–1,000 msec, echo-train length of approximately 128, and 0.5 signal acquired were used.
In an attempt to maximize diagnostic information, in most patients the images were obtained with several techniques. In general, the best spatial resolution was obtained with respiratory triggering, but gating could not be adequately performed in all patients. Single-shot technique was used in those infants who were not sufficiently sedated to allow a respiratory-triggered study that required longer imaging time. MR cholangiography was well tolerated in all patients.
Standard criteria were defined and used to interpret the original studies. A study finding was considered normal if the extrahepatic central biliary ducts (right, left, and common hepatic) and the common bile duct were visualized and the ducts were 4 mm or less in diameter with confluent, uniform branching. A study finding was interpreted as consistent with EHBA if any portion of the extrahepatic central biliary duct or the common bile duct could not be delineated, regardless of whether if the gallbladder was present. A study finding was interpreted as abnormal but not consistent with EHBA if the biliary system was demonstrated but the gallbladder was absent. A study finding was considered equivocal if the spatial resolution was limited due to motion or other technical factors or if portions of the biliary system were seen but continuity could not be established. A choledochal abnormality was defined as saccular dilatation of the common bile duct with or without intrahepatic biliary dilatation or cysts.
We (K.I.N., R.B.G., J.S.L.) retrospectively analyzed the original MR interpretations, which were monitored and read by one observer (K.I.N.), with the clinical diagnosis assessed by means of consensus (D.K., S.E., B.L.S.) to determine the accuracy of MR cholangiography in depicting EHBA and in helping to distinguish it from other causes of neonatal cholestasis. The sensitivity, specificity, and positive and negative predictive values of MR cholangiography for depicting EHBA were determined with standard Bayesian analysis. Any equivocal cases or those lost to follow-up were excluded. A waiver of informed consent for the chart review was obtained from our institutional review board for this study.
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RESULTS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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Two study findings were interpreted as abnormal but not consistent with EHBA. In these cases, no gallbladder was found at MR cholangiography. In one patient, a biopsy finding was consistent with nonspecific hepatitis that has subsequently resolved (Fig 1). The other patient underwent a Kasai operation at another institution for presumed EHBA. Pathologic examination revealed partial preservation of the extrahepatic duct lumen (Fig 2), a paucity of intrahepatic bile ducts, and a collapsed gallbladder.
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Two images were considered equivocal or nondiagnostic. Both images were of poor quality because of motion artifact. In one image, portions of the biliary system were seen but spatial resolution prevented establishment of continuity. The patient died of a mitochondrial disorder. In another image, a cyst was seen adjacent to the common duct, and a choledochal cyst was suspected. Again, spatial resolution was poor because of motion. At laparotomy, this cyst was defined as a remnant of the extrahepatic biliary system, and the patient underwent a Kasai operation.
Four images revealed choledochal cysts that were questioned at prior US examinations. MR cholangiograms helped to confirm the diagnosis and provided anatomic detail that was useful for surgical planning. All cysts, including a type 4 choledochal abnormality, were confirmed at surgery. Although intra- and extrahepatic biliary dilatations were seen at US in this patient, the intrahepatic cysts were not seen. This patient was therefore not considered for portoenterostomy and has successfully undergone liver transplantation (Fig 4) (4).
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DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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Despite recent reports that visualization of a fibrotic triangular cord that is cranial to the portal vein bifurcation, combined with measurement of short gallbladder, is highly suggestive of EHBA (7,8), US is frequently not diagnostic and allows limited anatomic delineation of the biliary system (6). Hepatobiliary imaging is beset by frequent false-positive findings and delays secondary to phenobarbital induction (9,10). Endoscopic retrograde cholangiopancreatography is invasive, requires general anesthesia, and is subject to substantial morbidity (0.8%–7.0%), technical failure (3%–9%), and occasional mortality (0.05%–1.00%) (13,14). Liver biopsy is invasive. For the diagnosis of EHBA, liver biopsy has a reported sensitivity of up to 100% and a specificity of 75.9% (15). Although supportive of clinical diagnoses, biopsy alone is not diagnostic (16).
MR cholangiography is a well-established noninvasive modality used to define the biliary system in children (3, 17–20). Previous authors (3,18) have reported that EHBA can be reliably diagnosed at MR imaging on the basis of nonvisualization of either the common bile duct or the common hepatic duct. Our false-positive findings indicate that these criteria alone cannot be relied on for a 100% accurate diagnosis. By using our expanded criteria, which required delineation of the right and left hepatic ducts in addition to delineation of the common ducts, the positive predictive value of MR cholangiography was 75% (nine of 12). The erroneous diagnosis of EHBA was made in three infants. One infant, in whom the common duct was not visualized, had a rare defect in bile acid biosynthesis. In the other two infants, both with severe cholestasis, the common ducts were seen but the right, left, and common hepatic ducts were not seen. These three cases indicate a potential pitfall in the diagnosis of EHBA with MR cholangiography, which relies on the production and excretion of bile for visualization of the biliary system. The appearance of EHBA may be simulated if insufficient bile is produced.
Strict criteria were adhered to in reporting interpretations of the images of a patient’s MR study as consistent with EHBA. The definition of a normal caliber duct was based on previous US studies in children (21). By using our criteria, MR cholangiography had at least 90% sensitivity (nine of 10) and 77% specificity (10 of 13) in the depiction of EHBA, but not 100% accuracy. These data are similar to those described for other diagnostic techniques, including hepatobiliary imaging (9,10), endoscopic retrograde cholangiopancreatography (11), and liver biopsy (15). Except in one case, the delineation of right, left, common hepatic, and common bile ducts excluded the possibility of EHBA, with a negative predictive value of 91% (10 of 11). In the false-negative case, partial preservation of the extrahepatic bile duct lumen was present at pathologic examination and accompanied by intrahepatic paucity of the bile ducts. The term extrahepatic in biliary atresia is a misnomer, because the disease includes a spectrum of obliterative cholangiopathy that involves all or part of the extrahepatic ducts and, in some cases, extends to the intrahepatic ducts (22).
EHBA with duplication of the common bile duct has recently been described in the pathology literature and is another possible explanation for the false-negative results at MR cholangiography (23). Using our expanded criteria, we correctly identified three additional cases of EHBA in which the common duct was visualized but the right, left, and common hepatic ducts were not seen. Expansion of the MR criteria is supported by findings of endoscopic retrograde cholangiopancreatographic studies of EHBA, in which opacification of the common duct, the gallbladder, and a segment of the main hepatic duct is seen in up to 30% of cases (11).
A major contribution of MR cholangiography to the clinical treatment of infants with cholestasis is the avoidance, in numerous cases, of exploratory laparotomy and its inherent risks. No patient underwent an exploratory laparatomy after MR cholangiography revealed a normal biliary system. In addition, exploratory laparotomy was deferred in those infants who presented at older than 3 months, with findings on MR cholangiograms consistent with EHBA. A reliable diagnostic test for EHBA is particularly important in this clinical setting, since the likelihood of a successful hepatic portoenterostomy at this age is less than 25%, and exploratory laparotomy in this setting has increased morbidity owing to complications of advanced liver disease (24).
In contradistinction to a previous report (3), we found that the delineation of a normal gallbladder was not essential for the clinical diagnosis of neonatal hepatitis. Finally, MR cholangiography was also useful in confirming choledochal abnormalities that were depicted with US and in revealing anatomic details of these lesions, which are important for preoperative planning.
MR interpretations in this report were made by radiologists who were not blinded to clinical information. Hence, it can be argued that they may have been biased in their original interpretations. The interpretations were, however, made with defined criteria before outcome information was known. Therefore, we believe that comparison of MR interpretations with the clinical outcome in a realistic clinical setting has validity.
In contrast to previous reports, our experience is that the sensitivity, specificity, and positive and negative predictive values of MR cholangiography in the depiction of EHBA are similar to those of other established modalities (3,18). We acknowledge that our sample is small for statistical analysis, and these results are preliminary. MR cholangiography, however, offers many advantages over other diagnostic modalities. MR cholangiography can obviate more invasive procedures and does not require pretreatment, use ionizing radiation, or require general anesthesia in neonates.
The documentation of an intact biliary system with MR cholangiography was considered sufficient to exclude EHBA; thus, intraoperative cholangiography was avoided. Demonstration of a normal common bile duct did not necessarily exclude EHBA, as the disease may involve only the proximal extrahepatic biliary system; thus, the MR criteria should be expanded. We believe that MR cholangiographic findings must be interpreted in conjunction with other diagnostic and clinical information to successfully diagnose EHBA and distinguish it from other causes of neonatal cholestasis.
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FOOTNOTES |
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Author contributions: Guarantors of integrity of entire study, K.I.N., R.B.G., B.L.S.; study concepts and design, K.I.N., B.L.S.; literature research, K.I.N., R.B.G., B.L.S.; clinical studies, K.I.N., R.B.G., D.K., S.E., B.L.S.; data acquisition, all authors; data analysis/interpretation, K.I.N., J.S.L.; statistical analysis, K.I.N.; manuscript preparation, K.I.N.; manuscript definition of intellectual content, all authors; manuscript editing, K.I.N., R.B.G., B.L.S.; manuscript revision/review and final version approval, all authors.
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REFERENCES |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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[30,266 effective]/96.1 [effective], 3-mm-thick with no intersection gap) shows a cystic remnant (arrow) of the biliary system above the porta hepatis. No gallbladder, hepatic, or common ducts are identified. The infant had a confirmation of EHBA during exploratory laparotomy and underwent a Kasai operation.