Intraductal Ultrasonography of the Bile Duct System

Objectives and Basic Principles

The ultrasonic miniprobe is an ideal instrument for insertion into fluid-filled tubular structures such as the bile duct system which are only slightly larger in diameter than the miniprobe itself. Possible clinical indications for miniprobe ultrasonography of the biliary tract are (i) bile duct strictures, and (ii) choledocholithiasis. The technique of intraluminal ultrasonographic imaging is called “intraductal ultrasonography” (IDUS) [[1] [2] [3] [4] [5] [6] [7] [8] [9] [10] ].

Bile duct strictures. Based upon anatomical bile duct structure and generally accepted endosonographic criteria for description of bile duct tumors, IDUS allows for accurate diagnosis of bile duct strictures. An improved management of extrahepatic bile duct carcinoma is based upon progress in diagnosing benign and malignant biliary stenosis and in the assessment of locoregional tumor extension. Although conventional ultrasonography (US) and computed tomography (CT) are accurate in diagnosing dilatation of bile ducts, assessment of the tumor extension around the hepatoduodenal ligament is difficult. Endoscopic retrograde cholangiopancreatography (ERCP) alone is accurate in topographical detection of biliary obstruction. However, ERCP is not precise enough in the locoregional staging of bile duct tumors.

For these reasons, ultrasonic miniprobes attract special interest, as the probes are slim enough (diameter 1.2–3.4 mm) to be inserted into the bile duct system via the tract of a percutaneous transhepatic biliary drainage (PTBD) or via a transpapillary route through the working channel of a duodenoscope during ERCP [[1] [2] [3] [4] [5] [6] [7] [8] [9] [10] ]. Compared with standard endoscopic ultrasonography (EUS), intraductal scanning within the bile duct stricture itself enhances diagnostic accuracy significantly (89.1% vs. 75.6%; P<0.002) [[5]]. Although ultrasonography obviously does not provide a histopathological diagnosis, IDUS allows for some tissue characterization and thus may point to the underlying disease.

Choledocholithiasis. In patients with persistent pain and dilated bile ducts following cholecystectomy, high-resolution intraluminal ultrasonography might be useful. In such cases, IDUS can reveal, for instance, stones which are not detectable ductographically Intraductal sonographic evidence of stones can thus establish the indication for endoscopic sphincterotomy Though IDUS has been reported to be superior to ERCP in the detection of bile duct stones (96.8% vs. 80.6%) [[6]], surgically controlled prospective data are not yet available.

References

• 1 Tamada K, Ido K, Ueno N, et al. Preoperative staging of extrahepatic bile duct cancer with intraductal ultrasonography.  Am J Gastroenterol. 1995;  90 239-246
• 2 Inui K, Nakazawa S, Yoshino J, et al. Ultrasound probes for biliary lesions.  Endoscopy. 1998;  30 A120-A123
• 3 Tamada K, Tomiyama T, Ichiyama M, et al. Influence of biliary drainage catheter on bile duct wall thickness as measured by intraductal ultrasonography.  Gastrointest Endosc. 1998;  47 28-33
• 4 Tamada K, Ueno N, Tomiyama T, Oohashi A, et al. Characterization of biliary strictures using intraductal ultrasonography: comparison with percutaneous cholangioscopic biopsy.  Gastrointest Endosc. 1998;  47 341-349
• 5 Menzel J, Poremba C, Dietl KH, Domschke W. Preoperative diagnosis of bile duct strictures - comparison of intraductal ultrasonography with conventional endosonography.  Scand J Gastroenterol. 2000;  35 77-82
• 6 Menzel J, Domschke W. Gastrointestinal miniprobe sonography.  Am J Gastroenterol. 2000;  95 605-616
• 7 Tamada K, Wada S, Ohashi A, et al. Intraductal US in assessing the effects of radiation therapy and prediction of patency of metallic stents in extrahepatic bile duct carcinoma.  Gastrointest Endosc. 2000;  51 405-411
• 8 Inui K. Three-dimensional intraductal ultrasonography.  J Gastroenterol. 2000;  35 951-952
• 9 Tamada K, Nagai H, Yasuda Y, et al. Transpapillary intraductal US prior to biliary drainage in the assessment of longitudinal spread of extrahepatic bile duct carcinoma.  Gastrointest Endosc. 2001;  53 300-307
• 10 Tamada K, Kanai N, Wada S, et al. Utility and limitation of intraductal ultrasonography in distinguishing between longitudinal cancer extension along the bile duct and inflammatory wall thickening.  Abdom Imaging. 2001;  26

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Comment on: Leung JW, Neuhaus H, Chopita N: Mechanical lithotripsy in the bile duct. Endoscopy 2001; 33: 800–804

To undertake therapeutic biliary endoscopy without access to mechanical lithotripsy is akin to taking a 1000 km driving tour in a convertible: you only need the top up when it is raining/snowing/cold/or the weather is otherwise inclement. In other words, you can perform ERCP perfectly well without a mechanical lithotriptor — most of the time. Until you need it. And then it becomes the roof of the convertible.

Or, you have alternatives for large calculi: stents or nasobiliary drains to bypass the stones; dissolution agents, either oral (ursodeoxycholic acid) or intra-ductal (mono-octanoin, ? methyl-tert-butyl ether); surgery; or other forms of lithotripsy (electrohydraulic, laser, or extracorporeal shock wave lithotripsy).

These latter forms of stone fragmentation are considerably more resource intensive and expensive than mechanical lithotripsy and application of the dissolution agents is, at times, equivalent to placing a rock into a glass of water and awaiting its ultimative but inevitably slow dissolution. Nor will stents or drains help you with a basket impaction or be satisfactory long-term therapy for any but the very infirm patient.

Drs. Leung, Neuhaus, and Chopita put mechanical biliary lithotripsy into perspective in this article, truly emphasizing the Expert Approach and the benefits and limitations of the various available technologies and application techniques. For those of us immersed in the care of patients with pancreaticobiliary disorders, knowledge of these lithotriptors is as essential as knowing that a patient has an allergy to an antibiotic or a bleeding diathesis. How does one disimpact a stone without access to a Soehendra lithotriptor? Anwer: don't impact it in the first place, something easier said than done. How does one pull a sharply angulated, 2 cm stone through a 1 cm distal bile duct without some form of fragmentation, usually with the through-the-scope Olympus lithotriptor, at least in our unit?

So take your 1000 km road trip and leave your lithotriptor at home. But, both you and your passengers (patients) should prepare to get sun burned, wet, and wind-blown, and colder than you ever thought possible.

Richard Kozarek, M.D., Chief of Gastroenterology,

Virginia Mason Medical Center, Seattle, WA, USA.