PATIENT POPULATION

Seventy consecutive inpatients with suspected CBD stones were prospectively included in the study over a period of 12 months. There were 34 men and 36 women, mean (SD) age 71 (15.5) years (median 75, range 30–93). The patients were referred for direct cholangiography (or endosonography) because of cholangitis (33; 47%), acute pancreatitis (three; 4%), suspected post-cholecystectomy choledocholithiasis (nine; 13%), cholestasis (six; 9%), and stones suspected from ultrasound or computed tomography scan (19; 27%).

MAGNETIC RESONANCE CHOLANGIOGRAPHY

MRC examination was performed within the 12 hours preceding direct cholangiography on a 1.5 T unit (Siemens Magnetomvision, Munich, Germany) with a body coil. Patients did not receive antiperistaltic agents but fasted before MRC to reduce motion artefacts from bowel peristalsis. A preliminary MRC survey of the upper abdomen was first performed with heavily T2 weighted gradient echo sequences. MR cholangiograms were acquired using non-breath-holding fat suppressed respiratory triggered turbo spin echo (TSE) sequences. Two dimensional TSE imaging was performed in the axial and coronal planes; the latter were not parallel to the hilum. The source images obtained were reformatted into targeted small volume maximum intensity projection images when necessary to clarify the anatomy further. Twenty five oblique coronal source images with a 5 mm section thickness and no overlap were acquired. The imaging parameters were: repetition time/echo time, 4500 milliseconds/138 milliseconds; matrix, 174 × 256; acquisition time, 1 minute 53 seconds for each pile of sections (two or three piles were needed for biliary tree coverage).

The radiologists who performed the MRC were blinded to any radiographic information—that is, sonography and/or computed tomography (CT) scan results. The only information of which they were aware was the suspicion of CBD stones.

REFERENCE IMAGING METHODS

ERC was performed with TJF 100 or TJF 130 duodenoscopes (Olympus, Tokyo, Japan) in 63 patients. All procedures were carried out under general anaesthesia and using antibiotic prophylaxis. Endoscopic sphincterotomy was performed in 55 patients and endoscopic balloon dilatation in four; an instrumental exploration of the CBD with Dormia baskets and retrieval balloon passage through the bile duct was performed in all cases. The presence of CBD stones was confirmed on their removal or they were actually seen passing through the sectioned sphincter into the duodenal lumen. In four patients, the cholangiogram was normal and no endoscopic sphincterotomy was performed. In five patients, the diagnosis of choledocholithiasis was based on endosonography.1 Endoscopic ultrasonography was performed under general anaesthesia. The biliary tract was traced from the papilla of Vater up to the hepatic bifurcation. The left intrahepatic bile ducts were also examined. Two patients had intraoperative cholangiography during cholecystectomy.

IMAGE ANALYSIS

The magnification factor was corrected in the determination of CBD calibre on cholangiograms; CBD calibre was considered to be dilated if it was larger than 7 mm, except in patients after a cholecystectomy, in whom a CBD up to 9 mm in diameter was assumed to be normal. These criteria were also applied for endosonography and MRC measurements of the CBD. MRC and direct cholangiography images were separately interpreted by radiologists and endoscopists in a blinded fashion, and discrepancies among observers were settled by consensus. Both teams evaluated the following items: CBD calibre; level of obstruction if any; number, size, and location of intraluminal signal voids for MRC; number of filling defects and/or stones removed and their sizes and localisation within the CBD for ERC. The presence of gallstones, cystic duct calculi, bile duct strictures, dilated intrahepatic biliary tree, or associated lesions were also examined. The endoscopists were aware of all clinical, biochemical, and previous imaging findings except those of MRC.

JUDGMENT CRITERIA AND STATISTICAL ANALYSIS

The main judgment criterion was the information on the presence or absence of CBD stones yielded by MRC. Secondary criteria were: image diagnostic quality; accuracy of CBD assessment; ability to yield useful additional information. Descriptive statistics and rough data were used for the calculation of sensitivity, specificity, and positive and negative predictive values. The aim of the study was to provide a first evaluation of MRC as it is currently used in a university hospital with a conventional commercial magnetic resonance imaging (MRI) system. We considered that a minimal sample size of 50 patients would be sufficient to produce such information.

IMAGE DIAGNOSTIC QUALITY

MR cholangiograms giving complete delineation of the CBD were obtained in all cases and were technically adequate for interpretation. The quality of the images was considered to be good in 53 cases but only fair in 17 because of slight blurring.

Cholangiograms of diagnostic quality were obtained in all the patients who underwent ERC.

BILE DUCT CALIBRE (TABLE 1)

At ERC, endosonography, or intraoperative cholangiography, the CBD was found to be undilated in 24 patients (34%) and dilated in 46 (66%). MRC correctly identified normal calibre CBD, common hepatic and intrahepatic bile ducts in 22 cases (92%). In the five cases in which endosonography was the sole reference method used, the entire CBD was visualised as being of normal calibre and echo clear. The two patients who underwent intraoperative cholangiography also had a normal CBD. Thirty six patients (78%) with dilated CBD were correctly evaluated by MRC with regard to duct calibre. CBD diameter was overestimated by MRC in two patients (8%). One of these was found to have a choledochal cyst at ERC. A dilated CBD was interpreted as being normal at MRC in 10 patients (22%).

CBD STONES

Forty nine patients (70%) had CBD stones; stone size ranged from 1 to 20 mm (mean 6.1 mm, median 5.5 mm). A single stone (fig 1) was found in 17 patients (35%) (less than 6 mm in size in 10 patients and 8–20 mm in seven), and 32 patients had two or more stones. Twenty seven (55%) patients had stones smaller than 6 mm. Fourteen patients had more than five stones of smaller size (1–7 mm). Forty four patients (90%) had stones located in the CBD (six of which were impacted in the papilla), four had intrahepatic stones, and one had a stone in the cystic duct stump. In the 21 remaining patients, direct cholangiography (or endosonography in five cases) gave negative results for CBD stones; however, nine patients (13%) had endoscopic stigmata of stone migration (papillary oedema, gaping orifice, sludge in the CBD), and in one patient sphincter of Oddi dysfunction was diagnosed (bile duct dilatation above smooth terminal narrowing and delayed emptying). Two patients were found to have small intrapapillary cholangiocarcinomas and one patient had an external compression of the CBD. These findings were identified as such at MRC and confirmed by ERC. In eight patients (11%), the final diagnosis remained unclear.

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Figure 1

Coronal magnetic resonance cholangiography image showing a single 8 mm stone within the lower common bile duct. The common bile duct is slightly dilated (8.5 mm).

As mentioned above, all MRC images were adequate for interpretation in our study, although the quality of the images was reported as only “fair” in 17 because of slight blurring. Of these 17 cases, eight had calculi on standard examination and four of the eight were detected by MRC (50%). Stones in the four cases missed by MRC were as follows: a single 3 mm calculus, numerous 2 to 10 mm stones and a single 5 mm calculus of the CBD, and one 10 mm intrahepatic stone. Stones in the four cases detected by MRC were as follows: a single 4 mm calculus and two 10 mm stones in the CBD, and one 10 mm intrahepatic stone.

CORRELATION OF RESULTS FROM MRC WITH THOSE FROM THE REFERENCE METHOD (TABLE 2)

Of the 49 patients with biliary stone disease, 28 cases were identified by MRC and 21 cases of bile duct lithiasis were missed. The diameter of stones detected by MRC ranged from 2 to 20 mm. There were no false positive MRC results, giving 100% specificity, 57.1% sensitivity, 100% positive predictive value, and 50% negative predictive value.

STONES MISSED AT MRC (TABLES 3 AND 4)

The 21 cases of choledocholithiasis not detected by MRC comprised two patients with a single 4 mm intrapapillary impacted stone, seven with a single CBD stone (3–5 mm in size), three with numerous CBD stones (10–13 mm in size in two and 2–10 mm in size in one), seven with two or more stones of less than 6 mm within the CBD, and two with intrahepatic stones.

STONES MISSED AT MRC CORRELATED WITH CBD CALIBRE AND STONE SIZE (TABLE 5)

Of the 46 patients with a dilated CBD, 39 had CBD stones, and of these 39 patients, 24 (62%) were picked up by MRC (table 3). In the seven with a dilated CBD and no stones, MRC and ERC identified two small tumours of the lower CBD and one case of extrinsic compression of the CBD. The median size of stones in dilated CBD missed at MRC (15 cases) was 5 mm. Twenty four patients had a normal CBD calibre and 10 (42%) of these had ductal lithiasis. Stones in undilated CBD were seen at MRC in 4/10 cases (40%). The median size of the stones in undilated CBD that were missed at MRC (six cases) was 3 mm.