NORMAL STRUCTURES

There have been few studies of normal volunteers: Wallner et al’s early work with a 2D gradient echo technique3failed to identify the undilated biliary tree in three of five volunteers. Reinhold et al 13 compared a 3D gradient echo technique with a 2D MIP RARE technique in 26 patients with suspected bile duct abnormalities; a body coil was used for both sequences. The RARE approach consistently outperformed the gradient echo technique demonstrating one or more intrahepatic ducts, the extrahepatic ducts and a portion of the main pancreatic duct in 100%, 96% and 65% as opposed to 42%, 44% and 23% of patients, respectively. Using a 2D RARE breath-hold projection technique and a body coil, Laubenberger et al 16 demonstrated the undilated intrahepatic and extrahepatic ducts in all 30 normal volunteers studied. In the same study part or all of the main pancreatic duct was visualised in all the volunteers. Using a similar technique with a torso phased array coil, Lomas19demonstrated the normal pancreatic duct in 10 normal volunteers, showing the entire duct in eight, and the duct within the pancreatic head only in the remaining two.

NORMAL VARIANTS

Anatomical variants of the common bile duct and the insertion of the cystic duct are particularly important to the laparoscopic surgeon. Taourel et al,20 using a 3D MIP RARE technique with a torso phased array coil, successfully identified the cystic duct in 74 % of 171 patients: a low cystic duct insertion was shown in 11 (9%) of these patients, a medial cystic duct insertion in 22 (17%), a parallel course of the cystic and hepatic ducts in 31 (25%), and an aberrant right main hepatic duct in 12 (9%).

Using a non-breath-hold 3D MIP RARE technique and a body coil, Sotoet al 21 reported a sensitivity for detecting pancreas divisum of 66%. Improved results were achieved by Bretet al,15 using a similar approach but with a phased array torso coil and one or multiple breath-holds. They accurately identified pancreas divisum in six of 108 patients in whom ERCP correlation was also available.

BILIARY OBSTRUCTION

Although the earlier gradient echo techniques could detect the presence of biliary obstruction in 100%4-6 and its level in up to 90%5 of cases, they could not be used to determine accurately the underlying cause of obstruction and high grade stenosis and complete obstruction were difficult to distinguish. Improved results were again achieved with RARE based techniques. The largest series of 126 patients,10 with good correlation of the findings, used a 3D MIP RARE technique with a phased array torso coil. Imaging was performed with an extended breath-hold (64 seconds, 100% oxygen presaturation) or quiet respiration. Obstruction was identified with a sensitivity, specificity and accuracy of 91%, 100% and 94%, respectively. The diagnosis of the underlying aetiology of the obstruction was identified with positive and negative predictive values of 93% and 94% for calculi, and 86% and 98% for malignant stricture. In addition, MRCP routinely identifies the dilated biliary tree upstream of an obstruction, allowing synchronous strictures to be identified. This is not always possible with ERCP where visualisation of an obstructed part of the biliary tract may not be possible.

Using a rapid breath-hold 2D RARE projection technique with a body coil, Laubenberger et al 16 diagnosed with 100% accuracy the presence of obstruction, its level and extent and the underlying aetiology in all 30 patients when compared with ERCP. The undilated ducts downstream of the obstruction could be identified in addition to the dilated obstructed ducts upstream. Figures 1 and 2 are of patients with biliary obstruction imaged using a similar technique.

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Figure 1

: An oblique sagittal MRCP projection image obtained in a 16 second breath-hold in a 72 year old man with obstructive jaundice owing to multiple common duct calculi, confirmed at ERCP.

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Figure 2

: A 41 year old man with multiple hilar biliary strictures secondary to right hepatic artery occlusion. (A) Coronal MRCP image obtained in a 16 second breath-hold which demonstrates the strictures and the dilated obstructed left biliary ducts (arrows) not visualised on (B) the corresponding ERCP examination.

CHRONIC PANCREATITIS

The main indications for ERCP in chronic pancreatitis are to assist the diagnosis, and to detect anatomical variations such as pancreas divisum. ERCP plays a key part in the diagnosis of chronic pancreatitis,^{22 23} although the radiological findings in mild disease are inconsistent.24

MRCP has not been to shown to have a role in mild disease and currently has limited spatial resolution for demonstrating side branch abnormalities (fig 3). MRCP may be of value in the diagnosis of moderate and severe disease when main duct abnormalities and filling defects may occur. Soto et al used a respiratory triggered 3D MIP RARE technique to image the pancreatic duct during quiet respiration,21 achieving a sensitivity of 87–100% for duct dilatation, and a sensitivity and specificity of 75% and 69%, respectively, for stricture detection, although the latter was increased to 81% by reviewing the source images themselves. Takeharaet al assessed a breath-hold 3D MIP RARE technique with a phased array surface coil in 39 patients with known severe chronic pancreatitis.9 Agreement with ERCP in this selected group was 82–92% for ductal dilatation, 70–92% for ductal narrowing and 92–100% for filling defects with low interobserver variation overall.

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Figure 3

: A 48 year old man with severe chronic pancreatitis. An axial image from his MRCP examination demonstrates the abnormally dilated main duct and side branch ducts in the pancreatic tail (arrows) which could not be demonstrated at ERCP.

ACUTE AND RECURRENT PANCREATITIS

ERCP may be used to detect an underlying cause for acute or recurrent pancreatitis, particularly choledocholithiasis, and evidence suggests that early ERCP and sphincterotomy may be beneficial,25 although it is associated with an increased complication rate. As far as we are aware there have been no MRCP studies addressing this aspect, although anecdotally we have used MRCP successfully for recurrent pancreatitis to detect a communicating pseudocyst not demonstrated at ERCP.

AFTER FAILED ERCP

ERCP may be technically impossible after gastric or duodenal surgery where the antral and duodenal anatomy has been altered, and when normal variants or obstruction are encountered. Soto et al 27 studied 39 consecutive patients in whom ERCP had been unsuccessful using a non-breath-hold 3D MIP RARE technique and a body coil. MRCP was successful in all patients and of particular relevance is that normal examinations were obtained in 11 patients, and minor abnormalities requiring conservative management only in a further eight cases.

ERCP may fail to visualise parts of the biliary and pancreatic duct system upstream of an obstruction, making it difficult to exclude synchronous lesions and to plan appropriate therapeutic intervention. Because of the need at ERCP to pass the obstruction to inject contrast media, the visualisation of an obstructed upstream system in this way is associated with an increased risk of sepsis. In such cases MRCP has been shown to visualise reliably the upstream ductal systems often made more conspicuous by their increased diameter (fig2).18 ,26