EUS for bile duct stones: how does it compare with ERCP?

The clinical and biochemical manifestations of choledocholithiasis range from none to jaundice, cholangitis, and gallstone-induced pancreatitis. When the clinical features strongly suggest the presence of bile duct stones, management is fairly straightforward; diagnostic and therapeutic ERCP may in some cases constitute the entire strategy. Unfortunately, the clinical picture is often equivocal or uncertain. Although stones are unlikely to be present in the bile duct when the clinical index of suspicion is low, their presence can never be completely ruled out based on clinical and biochemical parameters. Thus, an accurate, noninvasive, reliable, and safe method for bile duct imaging would be highly advantageous, particularly when laparoscopic cholecystectomy is contemplated. The accuracy of currently available noninvasive imaging studies for the diagnosis of choledocholithiasis, with the possible exception of magnetic resonance cholangiopancreatography (MRCP), is unsatisfactory. ERCP is relatively reliable and highly accurate in relation to CT and transabdominal US and offers the prospect of immediate and definitive therapy in the event ductal stones are demonstrated, but it is the most invasive of available methods, having the highest complication rate. In cases in which there is only a moderate or even low suspicion that bile duct stones are present, the risk-benefit ratio of ERCP becomes especially problematic. EUS is a potential alternative to ERCP, one that is relatively less invasive with a risk of complications similar to that of upper endoscopy. Either a dedicated echoendoscope or a US catheter probe can be used to image the bile duct. Most available data pertain to the mechanical sector scanning echoendoscope, an instrument system that provides a 360 degree scan perpendicular to the axis of the endoscope insertion tube. Although the bile duct can be imaged from the descending duodenum with this instrument, proper positioning in the duodenal bulb often reveals the entire length of the bile duct. A stone in the duct appears as a reproducible, hyperechoic focus with associated acoustic shadowing. Catheter US probes are designed for insertion through the accessory channel of standard endoscopes including duodenoscopes. However, deflection of the US catheter with the elevator at the tip of a duodenoscope can damage the catheter. This problem was significantly reduced by the incorporation of a rail-type system at the end of the probe which allows insertion over a guidewire. Most catheter EUS systems use a higher US frequency (20 or 30 MHz) relative to that offered by dedicated echoendoscope systems. Since the first report of EUS in the diagnosis of choledocholithiasis in 1992 by Edmundowicz et al.,1 the results of 8 prospective, controlled trials (2 from a single group; 2 multicenter)2-9 and 1 retrospective study10 of EUS in patients with suspected bile duct stones have been reported. Although differing in design, all studies found EUS accuracy comparable to that of ERCP for the diagnosis and exclusion of choledocholithiasis. The echoendoscopes used in all studies were radial scanning instruments, but comparable accuracy was obtained in a single study that used a linear scanning echoendoscope.11 A limitation of these studies is that cholangiography, either endoscopic retrograde (ERC) or intraop