British Journal of Radiology (2004) 77, 1059-1064
© 2004 British Institute of Radiology
doi: 10.1259/bjr/34655158
Magnetic resonance cholangiography in children
C Metreweli, FRCR,
N M C So, FRCR,
W C W Chu, FRCR and
W W M Lam, MD
Department of Diagnostic Radiology and Organ Imaging, The Chinese University of Hong Kong, Prince of Wales Hospital, Ngan Shing Street, Shatin, NT, Hong Kong
Correspondence: Dr W W M Lam
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Abstract
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Magnetic resonance cholangiography has been shown to be useful in the evaluation of hepatobiliary problems in paediatric patients. Its clinical application in biliary atresia, choledochal cyst, cholelithiasis, bile plug syndrome and liver transplant are illustrated by the following cases.
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Introduction
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Magnetic resonance cholangiography (MRC) is now establishing itself as a viable alternative to endoscopic retrograde cholangiopancreatography (ERCP) in adults, particularly in the diagnosis of choledocholithiasis. In children, even in experienced hands, ERCP is difficult and hazardous, with a 90% success rate and a 33% complication rate compared with adults. Therefore, non-invasive and non-irradiating imaging investigations are important for patient's management. Currently most centres would use ultrasound and/or MRC as non-invasive investigation in hepatobiliary problem in paediatric patients.
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Technique
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Preparation
Fasting is essential in order to fully distend the gallbladder and biliary system, empty the stomach of contents (which may overlap or cause ghost artefacts) and reduce intestinal motility. Use of negative paramagnetic agents to suppress fluid in the duodenum or proximal small bowel might improve visualization of the common pancreaticobiliary channel.
Sequences
The basic principle underlying the MRC sequences is to use a heavily T2 weighted sequence with fat suppression, so that slow moving or static fluid will give a high signal intensity, whereas surrounding tissues will give a much lower signal. Non-breath-hold techniques usually use fast-spin echo two-dimensional (2D) or 3D sequences and data are acquired in the coronal plane with respiratory gating. Longer echo time (TE) values and thin (<1 mm) overlapping slices are preferred if the final images will be displayed as multiple intensity projection (MIP) reconstructions. A regular breathing pattern is required. The data acquisition time can be more than 10 min. However, the volume of coverage is not limited by the breath-hold duration [1].
Breath-hold techniques are faster but less suitable for infants and young children as they cannot co-operate [2]. Single thick slab and multiple thin slabs can be acquired. A thick slab up to 4 cm thick can be acquired in about 2 s with a heavily T2 weight turbo spin echo (TSE) sequence. The thick slab is usually acquired in the coronal plane and can be repeated at multiple degrees of obliquity at 10–15 degree intervals. A plane, which optimally demonstrates the lesion, can then be chosen so that thin contiguous slices can be acquired to further evaluate the area in question. Multiple thin slices, 3–4 mm thick acquired in less than a second each can be obtained with half-Fourier single shot sequence (HASTE) or single shot fast spin echo (SSFSE). The HASTE technique is superior to the heavily T2 weighted fast spin echo technique in demonstrating the anatomy of the biliary tree and its surrounding structures. Additional data acquisition in the decubitus position may be required in cases, where it is uncertain if aerobilia or cholelithiasis is present.
Image reconstruction and evaluation
The selection of viewing method is critical as different presentation can enhance or diminish the conspicuity of the lesion in question. The data can be viewed as thin slice source images, MIP (as a single or Raysun multiple projections) or volume rendering.
For demonstration of the gross anatomy of the biliary tract, thick slab MIP or volume rendering would be preferred. If there is suspicion of cholelithiasis or stenosis clinically, from the thick slab or post-processed images, then review of the source images and thin slice sections are necessary.
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Clinical applications
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Biliary atresia
The differentiation of biliary atresia from neonatal hepatitis remains a common diagnostic problem. Cholescintigraphy has been the mainstay of primary diagnosis until recently, despite a false positive rate of around 30% [3]. Ultrasound can make the diagnosis in most of the cases [4], though liver biopsy might be necessary in the diagnosis of extrahepatic biliary atresia. Despite the small size of the biliary ducts and motion artefact there have been reports suggesting that MRI might be useful. The extrahepatic bile ducts including the gall bladder, the cystic duct, the common bile duct and the common hepatic duct are visualized by MRC in neonates without biliary atresia in 96% (Figure 1
). MRC had an accuracy of 98%, sensitivity of 100% and specificity of 96% for diagnosing biliary atresia as the cause of infantile cholestatic jaundice [5].
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Figure 1. Magnetic resonance cholangiography (MRC) of a 2-month-old baby who has suspected biliary atresia diagnosed by ultrasound. Maximum intensity projection images of MRC showed normal biliary system and normal gallbladder (*).
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The signs looked for are similar to ultrasound: absence of visualization of the main ducts, a small gall bladder (Figure 2) and a high signal triangular area anterior to the porta hepatis seen in T2 weighted images. Similar areas of high signal intensity were not seen on T2 weighted images in neonatal hepatitis and in about 33% of neonates with proven biliary atresia. Thus, this sign is highly specific but not as sensitive.
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Figure 2. A 1-year-old boy with biliary atresia diagnosed at birth and surgery refused. Admitted for increase in jaundice. Maximum intensity projection images of magnetic resonance cholangiography (MRC) showed marked dilatation of left (*) and right intrahepatic ducts (#) with absence of common bile duct and gallbladder.
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In addition, significant periportal thickening is seen in some patients. This corresponds to periportal fibrosis. MRI is more sensitive in detecting this sign than ultrasound [6].
Periportal fibrosis manifested as low signal in the periportal region on echo gradient turbo fast echo (TFE) T1 sequence, which disappear after gadolinium injection (Figure 3).
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Figure 3. A 15-year-old boy with long standing biliary atresia post Kasai operation. (a) Pre contrast T1 sequence shows linear hypointensity (arrow), which (b) disappears after gadolinium administration. This is likely to represent fibrosis, the fact that it extends to the periphery of the liver may be related to the surgical intervention. Also note the slightly irregular liver edge (arrowhead) and splenomegaly (*).
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Choledochal cyst
The bile duct dilatation can involve the extrahepatic, intrahepatic or both portions of the biliary tree. The diagnosis of a choledochal cyst is usually first identified with ultrasound. Specific diagnosis of choledochal cyst was possible with the demonstration of direct entrance of the extrahepatic ducts into the cyst [7] (Figure 4). Additional items of information that may be of interest at first diagnosis are: any stenotic lesions of the intrahepatic ducts or associated Caroli's disease, which may require separate drainage or modification of the usual procedure; the presence of an anomalous pancreaticobiliary channel; cholelithiasis, and anomalous hepatic biliary ducts. In neonates the possibility of concomitant choledochal cyst and biliary atresia is an additional problem.
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Figure 4. A 1-year-old boy with choledochal cyst. Maximum intensity projection images of magnetic resonance cholangiography shows involvement of both the common hepatic duct (#) and common bile duct (*).
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A number of studies have reported the use of MRC in children with choledochal cysts with the largest series [8] involving 14 children. All have been able to define the presence of the cyst and identify the Todani type. Reports on the ability to visualize the common pancreaticobiliary channel give sensitivity varying from 0 to 100%. MRI may be useful in differentiating cystic lesions found in the liver when the differential includes Caroli's disease, autosomal recessive polycystic kidney disease (ARPKD), sclerosing cholangitis in Langerhan's cell histiocystosis, and biliary atresia associated with cysts and pre-natally diagnosed choledochal cysts.
Caroli's disease, also referred as choledochal cystic disease Todani type V, is a rare congenital condition. It may be the result of a translocation [9]. It is characterized by multiple biliary strictures with saccular bile duct dilation (Figure 5). The distribution can be monolobar or bilobar [10]. This abnormality has a generally poor but very variable prognosis [11]. It leads to intrahepatic cholelithiasis, recurrent cholangitis usually presenting in the first year of life. While hepatic fibrosis, biliary cirrhosis, portal hypertension and biliary malignancy develop in later life. It may also be associated with choledochal cyst, a variety of renal anomalies, autosomal dominant polycystic kidney disease (ADPKD), ARPKD, sponge kidney, congenital hepatic fibrosis and syndromes such as Opitz trigonocephaly.
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Figure 5. A 10-year-old girl with Caroli disease. Maximum intensity projection images of magnetic resonance cholangiography shows multiple saccular dilatation of both left and right hepatic ducts.
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Cholelithiasis
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Biliary calculi and concretions may be located in the gall bladder, the main extrahepatic ducts or the intrahepatic ducts, where they will often be associated with strictures and dilations of the ducts. Ultrasound is very accurate in the detection of calculi in the gall bladder, but less so in the intrahepatic and extrahepatic ducts (Figure 6).
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Figure 6. Maximum intensity projection images of magnetic resonance cholangiography showing a large gallstone (arrow) in a 4-month-old baby with haemolytic disease.
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Choledocholithiasis
In adults the claims for the value of MRC are striking. The sensitivity, specificity, accuracy, positive predictive value and negative predictive value of MRC for choledocholithiasis were all greater than 90% [12].
Generally MRC, in adults, is considered to be more sensitive and specific than ultrasound for choledocholithiasis [13]. This has not yet been put to the test in children, but would seem to be worth considering when the possibility needs to be excluded and ultrasound is negative.
Bile plug syndrome
The presence of a bile plug in the extrahepatic biliary tract can cause cholestatic jaundice [14]. As this is commonly found in the common bile duct, which may be poorly visualized with ultrasound, MRC may be very useful in assessing its presence as bile plug can be detected as low signal filling defect, MRC is also useful for the delineation of the extent (Figure 7).
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Figure 7. Maximum intensity projection images of the magnetic resonance cholangiography of a 2-month-old baby showing multiple sludge in right hepatic duct (arrow) and common bile duct (arrow).
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Transplantation
In children with liver transplantation, ERCP is technically difficult where the bile duct drains into a Roux loop. In this population, the role of MRC may assume increased importance and may be useful to evaluate and to confirm a diagnosis of bile duct complication, such as dilatation, anastomotic stenosis, multiple bile duct stenosis, intrahepatic biliary calculi (Figure 8), acute cholangitis, and in resolving inconsistencies between ultrasound, liver function tests and liver biopsy [15]. MRI was far superior to ultrasound in the detection of chronic rejection, assessing biochemical abnormalities without biopsy evidence of rejection, and sepsis caused by surgically correctable strictures [16].
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Figure 8. A 14-year-old girl with biliary atresia and liver transplant. Maximum intensity projection images of magnetic resonance cholangiography showing a round biliary calculus (arrow) in proximal left hepatic duct.
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Conclusion
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Despite the potentially wide application of MRC in paediatric patients, resolution of the biliary system is affected by the small size of the ducts, partial volume averaging and motion blur related to respiratory and cardiac motion. Ducts less than 1 mm are not routinely visualized. Usually the first branch of the intrahepatic duct, the common hepatic duct and the common bile duct, in addition to the gall bladder will be demonstrated in most children and only the extrahepatic bile duct in the majority of neonates. With advances in technology such as the application of parallel imaging technology, there will be improvement in spatial resolution, shortening of scanning time and decrease in motion artefact. MRC might be expected to play an increasing role in assessment of paediatric hepatobiliary problems.
Received for publication March 16, 2004.
Revision received June 18, 2004.
Accepted for publication August 13, 2004.
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References
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Abstract
Introduction
