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1 Department of Radiology, Kobe Children's Hospital, 1-1-1 Takakuradai Suma-ku,
Kobe 654-0081, Japan.
2 Department of Pediatric Surgery, Kobe Children's Hospital, Kobe 654-0081,
Japan.
Received March 7, 2003;
accepted after revision May 14, 2003.
Address correspondence to K. Kanegawa.
Abstract
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MATERIALS AND METHODS. Fifty-five fasting infants with cholestatic jaundice were examined on sonography. The examinations focused on the visualization of the triangular cord sign and assessment of gallbladder length and contraction. The diagnosis of neonatal hepatitis or of other causes of infantile cholestasis was made if symptom resolution occurred during follow-up.
RESULTS. A triangular cord sign was found in 27 of 29 infants with biliary atresia and in one of 26 infants with neonatal hepatitis or other causes of infantile cholestasis. The diagnostic accuracy was 95%, sensitivity was 93%, and specificity was 96%. The gallbladder was thought to be abnormal if it was less than 1.5 cm long, was not detectable, or was detectable but had no lumen. The gallbladder was abnormal in 21 of 29 infants with biliary atresia, whereas it was abnormal in eight of 26 infants with neonatal hepatitis or other causes of infantile cholestasis. The diagnostic accuracy was 71%, sensitivity was 72%, and specificity was 69%. The gallbladder was detectable on sonography in 13 infants with biliary atresia and 26 infants with neonatal hepatitis or other causes of infantile cholestasis. Gallbladder contraction was not confirmed in 11 of 13 infants with biliary atresia and seven of 26 infants with neonatal hepatitis or other causes of infantile cholestasis. The diagnostic accuracy was 77%, sensitivity was 85%, and specificity was 73%.
CONCLUSION. The triangular cord sign was a more useful sonographic finding for diagnosing biliary atresia than gallbladder length and contraction.
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The aim of the present study was to evaluate the importance of the sonographic finding of the triangular cord sign relative to gallbladder length and gallbladder contraction in the diagnosis of biliary atresia in pediatric patients.
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Sonography was performed by two of the authors either using an SSD 500 sonographic machine (Aloka, Tokyo, Japan) and a 5-MHz convex transducer or a 7.5-MHz linear transducer or using a LOGIQ 500 sonographic machine (General Electric Medical Systems, Milwaukee, WI) and an 8.2-MHz linear transducer. All infants fasted for at least 3 hr before the examination but were allowed to drink milk during the procedure. The examination focused on visualization of the triangular cord and on assessment of the length and contraction of the gallbladder. The length and width of the gallbladder were measured on the maximal longitudinal image (Fig. 1). For evaluation of gallbladder contraction, the examination was repeated 60–90 min after the infant was fed.
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As described in previous reports
[1,
6–8],
the triangular cord was defined as a triangular- or tubular-shaped echogenic
density that was located immediately cranial to the portal vein bifurcation
and was 3 mm or more thick (Fig.
2). Detection of the triangular cord sign was defined as
indicative of biliary atresia, and the absence of the triangular cord sign was
interpreted as indicative of neonatal hepatitis or other causes of infantile
cholestasis. The gallbladder was thought to be normal if it was 1.5 cm or more
long (Fig. 3A); the gallbladder
was considered abnormal if it was less than 1.5 cm long, was not detectable,
or was detectable but had no lumen (Fig.
4A). An abnormal gallbladder is thought to be more suggestive of
biliary atresia than of neonatal hepatitis or other causes of infantile
cholestasis [7]. Gallbladder
contraction was evaluated by calculating the contraction index (CI) as
follows:
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The volume of the gallbladder was calculated using the following equation
[12]:
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The diagnosis of biliary atresia was confirmed at surgery, and the diagnosis of neonatal hepatitis or of other types of infantile cholestasis was confirmed by the resolution of symptoms on followup. Of 55 infants, 29 had biliary atresia, two had Alagille syndrome, and 24 had neonatal hepatitis or other causes of infantile cholestasis.
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Gallbladder Length
Among the 29 infants with biliary atresia, the gallbladder was considered
abnormal in 21 and normal in eight. In 16 of the 21 infants with an abnormal
gallbladder, the gallbladder was not detectable or was detected but had no
lumen. In the other five infants, the gallbladder was less than 1.5 cm long.
Among the 26 infants with neonatal hepatitis or other causes of infantile
cholestasis, the gallbladder was abnormal in eight and normal in 18. The
diagnostic accuracy of gallbladder length was 71%, sensitivity was 72%, and
specificity was 69%.
Gallbladder Contraction
In 11 of 13 infants with biliary atresia and a detectable gallbladder,
contraction was not seen. Gallbladder contraction was confirmed in only two
infants with biliary atresia. In seven of the 26 infants with neonatal
hepatitis or other causes of infantile cholestasis, gallbladder contraction
was not seen, and in the remaining 19 infants in this group, gallbladder
contraction was detected. The diagnostic accuracy of gallbladder contraction
was 77%, sensitivity was 85%, and specificity was 73%.
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Sonography is a simple and noninvasive method for evaluating cholestasis in infants. Occasionally, sonography detects other causes of infantile cholestasis such as a choledochal cyst. Performing sonography after the administration of phenobarbital is useful because phenobarbital enhances bile flow and improves the detectability of the gallbladder in severe neonatal hepatitis [4]. In the past, sonography was focused on the assessment of the length, contractility, or both of the gallbladder in fasting infants to distinguish biliary atresia from neonatal hepatitis. A small or undetectable gallbladder and the absence of gallbladder contraction were thought to be suggestive of biliary atresia. However, a small gallbladder or an uncontracted gallbladder may be seen both in biliary atresia and in neonatal hepatitis [3]. Furthermore, reports indicate that some patients with biliary atresia have a normal gallbladder [3, 7]. A gallbladder that is less than 1.5 cm long is suggestive of biliary atresia [2, 3], but biliary atresia associated with a gallbladder longer than 1.5 cm has been reported [7]. Based on the results of our series, the size of the gallbladder does not seem to be a decisive finding for the diagnosis of biliary atresia.
Contraction of the gallbladder has also been reported in patients with biliary atresia [12, 13]. One study showed that gallbladder contraction occurs in 9–20% of infants with biliary atresia [12], but the method of evaluating gallbladder contraction in that study is unclear. We adapted the contraction index and the normal ranges reported by Weinberger et al. [11]. Because these researchers reported contraction index data in 6-week-old and 4-month-old infants, we used the normal range for 6-week-old infants for patients younger than 12 weeks old and the normal range for 4-month-old infants for patients 12 weeks old or older. In our series, gallbladder contraction was not a satisfactory diagnostic sign. Gallbladder contraction was observed in two patients with biliary atresia in this series. In these patients, the morphologic type of porta hepatis was type IIIa and type IIIb of the Kasai classification [1]. Gallbladder contraction was previously reported to occur in patients with type IIIa porta hepatis [11, 12], in which the common bile duct is patent. In a patient with type IIIb porta hepatis, the common bile duct was microscopically measured as 50–300 µm; therefore, the mechanism of contraction is unclear.
Choi et al. [5] and Park et al. [6–8] reported a sonographic finding that they named the "triangular cord sign," which was a triangular- or tubular mass of fibrous tissue cranial to the portal vein bifurcation. Because of the high sensitivity, specificity, and diagnostic accuracy of this finding, these researchers concluded that the triangular cord sign was a useful sonographic finding for the diagnosis of biliary atresia. The triangular cord is thought to be the fibrous remnant of the duct in infants with biliary atresia. Park et al. [7] reported that the diagnostic accuracy, specificity, and sensitivity of the triangular cord sign was 93%, 83%, and 98%, respectively. The results of our study were similar to their findings. Two infants with biliary atresia in our series did not have a triangular cord: one had scanty fibrous tissue at surgery, and the other had virtually no fibrous tissue. Ohi [1] reported that the incidence of fibrous tissue at surgery was 67% in patients with biliary atresia, which would indicate that 33% of these patients had no triangular cord. However, our results and those of others show a higher incidence of the triangular cord in patients with biliary atresia (83–93%) than Ohi reported. In our series, there was one false-positive finding of triangular cord. Another such patient was reported previously, and the cause of the false-positive finding was thought to be periportal edema or thickening [7]. In our patient with the false-positive finding, follow-up sonography was performed twice and the triangular cord sign was seen at each examination. The gallbladder was considered abnormal because it was less than 1.5 cm long and contraction was negative. This patient had trisomy 13 syndrome and experienced cardiac dysfunction, but jaundice resolved spontaneously after 2 months. The cause of the false-positive finding is unknown, but periportal edema may have led to the detection of the triangular cord sign.
In conclusion, the diagnostic accuracy, specificity, and sensitivity of the triangular cord sign are superior to those of gallbladder length and gallbladder contraction, so the triangular cord sign seems to be the a more useful sonographic finding for making a diagnosis of biliary atresia than gallbladder length and contraction.
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