British Journal of Radiology 74 (2001),952-954 © 2001 The British Institute of Radiology
Improved diagnosis of extraheptic biliary atresia by high frequency ultrasound of the gall bladder
P Farrant, DMU1,
H B Meire, FRCR1 and
G Mieli-Vergani, MD, PhD2
1Department of Radiology and 2The Variety Club Children's Hospital, King's College Hospital, Denmark Hill, London SE5 9RS, UK
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Abstract
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Ultrasound scanning using a 13 MHz probe was performed on 158 infants, aged 12 weeks or less, presenting with conjugated hyperbilirubinaemia. The gall bladder was identified in 156 infants, 35 of whom had biliary atresia. The two patients in whom no gall bladder was seen both had biliary atresia. The gall bladder shape was normal in 128 patients (9 with biliary atresia) and irregular in 28 patients (26 with biliary atresia). The gall bladder wall was regular in 121 patients (4 with biliary atresia) and irregular in 35 patients (31 with biliary atresia). Combining these findings gave a sensitivity of 91.9%, a specificity of 96.7%, a positive predictive value of 89.5%, a negative predictive value of 97.5% and an accuracy rate of 95.6% for ultrasound of the gall bladder in the identification of biliary atresia. This compares with 90%, 92.4%, 75.3%, 97.3% and 91.9%, respectively, in our previous report using a 7 MHz probe.
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Introduction
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In a previous paper [1] describing the ultrasound features of the gall bladder in jaundiced babies, we stated that "Even higher frequency transducers have been developed since this study was undertaken and it is hoped that they will more clearly visualize gall bladder morphology". This study was performed to determine whether the ultrasound characteristics of the gall bladder using a higher frequency transducer, 13 MHz rather than 7 MHz, would improve our ability to distinguish between those patients who had biliary atresia and those who did not.
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Patients and methods
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In this prospective study, 160 patients, aged 12 weeks or less, with conjugated hyperbilirubinaemia were referred to the paediatric liver unit at King's College Hospital between April 1999 and December 2000 and underwent an ultrasound scan by one of two operators using a 13 MHz two-dimensional linear array probe (Siemens Elegra;Siemens Medical Inc, Erlangen, Germany). The patient selection criteria and method of scanning were unchanged from our previous study [1]. Patients were not routinely fasted before the scan, were never sedated and each patient received only a single scan.
A normal gall bladder is shown in Figure 1
. Figure 2 shows the irregular shape and wall thickness previously described to be associated with the gall bladder appearance in biliary atresia.
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Figure 1. Normal gall bladder. The gall bladder shape is regular and there is an identifiable wall structure of uniform thickness.
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Results
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Clinical follow-up and ultrasound data on gall bladder appearance were available in 158 of the 160 patients. Notes were not found for one patient and another had incomplete ultrasound data. The study group therefore included 158 patients and the ultrasound findings in these patients are summarized in Figure 3.
The gall bladder was identified in 156 (98.7%) of the 158 patients and was not seen in 2 (1.3%) patients. 35 of the 156 patients with an identifiable gall bladder had biliary atresia. The two patients in whom the gall bladder was not seen both had biliary atresia.
The shape of the gall bladder was regular in 128patients (9 with biliary atresia) and irregular in 28 patients (26 with biliary atresia).
The gall bladder wall had a normal regular appearance in 121 patients (4 with biliary atresia) and an irregular appearance in 35 patients (31 with biliary atresia).
There were 120 patients (3 with biliary atresia) in whom both a regular shaped gall bladder and a normal wall appearance were found, 27 patients (25 with biliary atresia) in whom both the gall bladder shape and wall were irregular, 8 patients (6 with biliary atresia) in whom the gall bladder shape was regular and the wall abnormal (Figure 4) and 1 patient with biliary atresia in whom the gall bladder shape was irregular and the wall appeared normal.
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Figure 4. Gall bladder in biliary atresia. The shape of the gall bladder is regular but there is absence of the normal wall structure.
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Using this combination of features of the gall bladder, a prospective diagnosis for the presence (figures in parentheses in Figure 3
) or absence of biliary atresia was attempted. The true and false positive and negative rates were calculated (Table 1). These give a sensitivity of 91.9%, a specificity of 96.7%, a positive predictive value of 89.5%, a negative predictive value of 97.5% and an accuracy rate of 95.6%.
There were four false positive patients who did not have biliary atresia but had a gall bladder that appeared abnormal on ultrasound. Three of these had non-specific neonatal hepatitis and one patient had cystic fibrosis.
Three patients with biliary atresia documented as having normal ultrasound appearances of the gall bladder were subsequently found to have macroscopically normal gall bladders at operation.
Of the 156 patients with a demonstrable gall bladder, the gall bladder lumen was fluid-filled in 122 patients but empty in 34 patients. 28 (23%) of the 122 fluid-filled gall bladders were in patients with biliary atresia and 7 (20.6%) of the 34 empty gall bladders were in patients with biliary atresia.
The ranges of the length and width measurements and the product of these diameters in patients with visible gall bladders are shown in Table 2.
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Discussion
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The 13 MHz probe improved the resolution in the imaging plane from that obtained previously with a 7 MHz probe. The two-dimensional feature enables the beam to be focused in the plane at right angles to the imaging plane and results in an improvement in both spatial and contrast resolution. With this improved imaging quality, the gall bladder was identified in 98.7% of patients and the wall of the gall bladder was seen in detail. The two patients in whom a gall bladder was not identified both had biliary atresia.
We correctly identified 117 (96.7%) of the 121 patients who did not have biliary atresia and who had a normal ultrasound appearance of the gall bladder, and 34 (91.9%) of the 37 biliary atresia patients who had an abnormal appearance or absence of the gall bladder.
The presence or absence of fluid within the gall bladder lumen was confirmed as being an unhelpful feature in distinguishing patients with biliary atresia, as 23% of the patients with fluid in the gall bladder lumen had biliary atresia and 20.6% with empty gall bladders had biliary atresia.
The gall bladder still tended to be smaller in patients with biliary atresia but there was no significant difference between the length, width or product of the diameters of abnormal gall bladders compared with those of normal gall bladders.
Using a cut-off measurement of 15 mm for gall bladder length, Tan Kendrick et al [2] found 12babies with biliary atresia, and the maximum length of the gall bladder was 14.5 mm. The 48patients who did not have biliary atresia had fasted gall bladder lengths ranging from 16–56.3 mm. In our study group the gall bladder length in the biliary atresia patients varied between 6.9 mm and 44.7 mm and in the non-biliary atresia patients between 10.5 mm and 47.6 mm. Had we used the 15 mm cut-off length described by Tan Kendrick et al, 4 patients would have been incorrectly diagnosed as having biliary atresia and 29 biliary atresia patients would have been missed.
Despite our improved results, we still believe that we will never achieve 100% accuracy, as a few biliary atresia patients have a normal gall bladder [3].
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Acknowledgments
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Professor Giorgina Mieli-Vergani is supported by the Children's Liver Disease Foundation, Birmingham, UK.
Received for publication May 16, 2001.
Accepted for publication July 5, 2001.
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References
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Farrant P, Meire HB, Mieli-Vergani G. Ultrasound features of the gall bladder in infants presenting with conjugated hyperbilirubinaemia. Br J Radiol 2000;73:1154–8.[Abstract]
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Tan Kendrick AP, Phua KB, Subramaniam R, Goh ASW, Ooi BC, Tan CE. Making the diagnosis of biliary atresia using the triangular cord sign and gallbladder length. Pediatr Radiol 2000;30:69–73.[Medline]
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Howard ER. Biliary atresia: aetiology, management and complication. In: Howard ER, editor. Surgery of liver disease in children. Oxford: Butterworth Heineman, 1991:39–59.
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September 1, 2007;
244(3):
845 - 851.
[Abstract]
[Full Text]
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Abstract
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