INTRODUCTION — The development of endoscopic ultrasound (EUS) in the early 1980s overcame some of the limitations of transabdominal ultrasound for imaging the gastrointestinal tract wall and retroperitoneum [1]. One of the advantages of EUS is the ability to apply the ultrasound transducer directly against the luminal surface, which minimizes intervening adipose tissue and air between the transducer and the target tissue, thereby enhancing image quality. The proximity of the transducer to the target tissue also permits the use of higher frequency ultrasound, which further contributes to the enhanced image resolution. As a result, EUS is used routinely in the evaluation of numerous gastrointestinal disorders, including the diagnosis and staging of gastrointestinal tumors. (See appropriate topic reviews.)
The technical evolution of EUS has led to the development of small caliber intraductal ultrasound (IDUS) miniprobes (about 2 mm), which can be passed through standard endoscopes directly into the bile or pancreatic duct (picture 1). The small caliber, flexibility, and excellent image quality produced by these catheters makes them ideal for evaluating a variety of biliary and pancreatic disorders (table 1).
This topic review will provide an overview of the role of IDUS in the evaluation of several pancreatic and hepatobiliary disorders. The role of standard EUS instruments in the evaluation of these conditions is presented separately. (See appropriate topic reviews.) The role of miniprobes for evaluation of other parts of the gastrointestinal tract is also discussed elsewhere. (See "High-frequency catheter endoscopic ultrasonography".)
TECHNICAL CONSIDERATIONS — Intraductal ultrasound (IDUS) is capable of producing better image resolution than standard endoscopic ultrasound (EUS; 0.07 to 0.18 mm) [2-4]. Acoustic coupling is optimized by the tubular anatomy of the pancreatic and bile ducts, which are fluid filled and only slightly larger in caliber than the probe itself. In addition, the probes operate at higher frequencies (12 to 30 MHz) than standard EUS, which leads to higher image resolution [5].
Three systems are available to perform IDUS (table 2):
●Electronic cylindrical phased array
●Combined probe (allows both radial and linear scanning)
●Mechanical radial sector scan system
Electronic systems — Electronic systems use thin catheters (diameter 1.1 mm, 3.5 French), have no rotating parts, and are extremely flexible. These probes contain a ring of 64 transducer elements that produce a 360º image. The transducer ring detects the signals from the tissue and transmits them via microwires to the image processor.
Mechanical probes — Components of mechanical probes include a single transducer, a wire to rotate the transducer, a cable that excites the transducer and transfers signals to the image processor, and a flexible protective housing. The rotating transducer is mounted on the tip of the wire and produces a 360º image.
Design variations exist for these catheter systems, some of which permit the use of a guidewire (picture 2). Single use probes are available in which a constant connection exists between the cable and the housing; the transducer rotates in a water-filled chamber whereas the shaft of the housing is free of fluid. Another multi-purpose catheter is available that requires insertion of the cable and transducer into a water-filled housing that may contain a distally attached balloon over the region of the transducer. This protective housing and balloon attachment helps minimize near field artifacts and reduces resistance during transducer rotation. Their design allows multiple uses and reduces the cost of this technology. Newer mechanical probes that permit mechanical rotating sector scanning and linear scanning have also been developed.
BILIARY TRACT INTRADUCTAL ULTRASOUND — Intraductal ultrasound (IDUS) can assist in the evaluation of patients with a variety of biliary tract disorders (table 1). The most common indications for IDUS of the biliary tract include the evaluation of choledocholithiasis and obstructive jaundice. IDUS is useful for determining the cause of biliary obstruction and can also assist in local tumor staging.
In contrast to endoscopic ultrasound (EUS), IDUS is often better able to evaluate the proximal biliary system and surrounding structures, such as the right hepatic artery, portal vein, and the hepatoduodenal ligament (image 1 and image 2). Examination of more distant tissues is hindered by its limited depth of penetration [6-9]. IDUS may also have limited value in evaluating lymph nodes, and unlike EUS, IDUS cannot be used to perform fine needle aspiration.
Technique — The IDUS catheter can be inserted into the bile duct through an endoscopic or percutaneous approach [10-13]. Endoscopic sphincterotomy was required in approximately 10 to 15 percent of patients undergoing IDUS during endoscopic retrograde cholangiopancreatography (ERCP) in initial reports [11,13]. New small caliber IDUS catheters permit cannulation without the need for sphincterotomy in almost all patients [12,14,15]. Severely stenotic strictures may require dilation with a catheter or balloon. The IDUS procedure time, including catheter insertion and imaging time, adds approximately 5 to 10 minutes to the duration of standard ERCP [13,16]. Complications attributed directly to IDUS are rare [12,13,16].
The normal bile duct appears as either two or three layers, which is similar to that seen during standard EUS [8,17-19]. The normal bile duct wall is 0.31 to 0.79 mm thick, with smooth inner and outer surfaces and homogeneous internal echoes [20]. When visualized as a two-layer structure, an internal hypoechoic layer is seen which represents the mucosa, muscularis propria (fibromuscular layer), and fibrous layer of the subserosa [21,22]. An outer hyperechoic layer represents the adipose layer of the subserosa, the serosa, and the interface echo between the serosa and surrounding organs. A third inner hyperechoic layer, representing an interface, will occasionally be identified. It may not be possible to differentiate the fibromuscular layer from the perimuscular connective tissue in some patients in whom they appear as a single hypoechoic layer. This limits the ability to differentiate between T1 and T2 bile duct cancers, although this distinction is usually not clinically relevant when considering treatment options [23].
Choledocholithiasis — A number of imaging modalities are available to evaluate patients with suspected choledocholithiasis, including transabdominal ultrasonography, computed tomography (CT), magnetic resonance cholangiopancreatography, ERCP, and EUS. (See appropriate topic reviews.) Initial studies have suggested a role for IDUS in patients with suspected choledocholithiasis who have normal cholangiography [24-27].
●One report included 62 patients who were suspected to have bile duct stones who underwent cholangiography and IDUS [24]. The presence of bile duct stones or sludge was confirmed after sphincterotomy. Overall, the combination of cholangiography plus IDUS was significantly more accurate than cholangiography alone for diagnosing bile duct stones (97 versus 87 percent).
●Another report included 31 patients with choledocholithiasis who underwent transabdominal ultrasonography, ERCP, and IDUS [25]. All patients underwent endoscopic sphincterotomy and stone removal to confirm the presence of bile duct stones. Wire-guided insertion of the IDUS catheter was possible in all patients. The sensitivity of IDUS was superior to ERCP and transabdominal ultrasonography (97 versus 81 and 45 percent, respectively). In the one patient in whom IDUS was falsely negative, the stone had migrated proximally into the left intrahepatic bile duct while only the right hepatic duct had been examined. A protocol requiring more complete bilateral examination may have permitted stone visualization. The sensitivity of IDUS over the other techniques was even higher for detecting small stones (<5 mm) and for determining the number of stones. IDUS reliably distinguished stones from sludge and air bubbles and there were no complications.
●A third report focused on 65 patients with suspected choledocholithiasis [26]. IDUS successfully identified all stones in 59 patients in whom choledocholithiasis was confirmed. Two false positive diagnoses were made in the remaining six patients, giving an overall sensitivity, specificity, and accuracy of 100, 67, and 97 percent, respectively.
●In a fourth report, IDUS was performed in 35 patients with suspected choledocholithiasis with equivocal findings on cholangiography [27]. Of 21 patients with apparent normal cholangiography, eight (38 percent) had stones or sludge detected by IDUS. All of these patients subsequently underwent sphincterotomy, which confirmed the presence of sludge or stones in seven. In contrast, IDUS permitted avoidance of sphincterotomy in five patients in whom a suspected stone on cholangiography was shown to be an air bubble by IDUS. Overall IDUS led to a change in clinical management in 13 patients (37 percent). However, the high rate of residual stones and sludge observed in this study compared with previous reports raise questions regarding the quality of the cholangiography [28]. Furthermore, the clinical significance of the residual sludge and stones is unclear since some of these may have been small enough to pass spontaneously.
Conclusions — IDUS can demonstrate common duct stones in patients suspected of having choledocholithiasis in whom stones are not visualized by other imaging modalities. However, at this point, the cost and absence of more data supporting its utility will likely limit its use in this setting.
Bile duct strictures — IDUS can help distinguish benign from malignant strictures based upon bile duct anatomy and unique sonographic imaging characteristics (image 3 and image 4) [6,16,29-35]. Causes of bile duct strictures include:
●Trauma (eg, cholecystectomy) (see "Complications of laparoscopic cholecystectomy")
●Anastomotic (see "Liver transplantation in adults: Long-term management of transplant recipients", section on 'Biliary complications')
●Primary sclerosing cholangitis (see "Primary sclerosing cholangitis in adults: Clinical manifestations and diagnosis")
●Autoimmune pancreatitis (see "Autoimmune pancreatitis: Clinical manifestations and diagnosis", section on 'Type 1 AIP')
●Chronic pancreatitis (see "Overview of the complications of chronic pancreatitis", section on 'Biliary obstruction')
●Cholangiocarcinoma (see "Clinical manifestations and diagnosis of cholangiocarcinoma")
●AIDS cholangiopathy (see "AIDS cholangiopathy")
●Infectious or ischemic cholangiopathy, including chronic bacterial cholangitis, recurrent pyogenic cholangitis, and biliary parasitosis (see "Recurrent pyogenic cholangitis")
●Pancreatic cancer (see "Clinical manifestations, diagnosis, and staging of exocrine pancreatic cancer")
●Lymphadenopathy (benign and malignant)
Findings suggestive of malignancy — IDUS criteria that suggest the presence of malignancy include [9,10,16,31,36]:
●A hypoechoic mass, especially if infiltrating surrounding tissues
●Heterogeneity of the internal echo
●Notching or irregularity of the outer border
●A papillary surface
●Disruption of the normal bile duct structure
●Suspicious lymph nodes (hypoechoic, round and smooth bordered)
Efficacy for diagnosing malignant strictures — The following reports illustrate the range of findings in the largest published series:
●One report included 56 consecutive patients with obstructive jaundice due to bile duct strictures in which a histologic diagnosis was available [16]. IDUS was significantly more accurate than EUS for determining the nature of bile duct strictures (89 versus 76 percent) (table 3). IDUS was also better able to determine the potential resectability of bile duct tumors and T stage (table 4). The advantage of IDUS was greatest for tumors located at the hilum or mid bile duct.
●Similar conclusions were reached in another study in which IDUS was compared to ERCP and tissue sampling in 30 consecutive patients with indeterminate bile duct strictures [14]. A malignant cause was demonstrated by histology in 18 patients. The final diagnosis was more accurately made with IDUS compared with ERCP with tissue sampling (90 versus 67 percent) (table 5). IDUS was superior to ERCP in regard to the sensitivity, specificity, and accuracy in the 21 patients who underwent both studies (table 6).
●A third series included 62 patients with suspected malignant strictures but with negative tissue sampling by ERCP [32]. The procedure could not be completed in two patients because the stricture could not be traversed with the ultrasound probe. The gold standard final diagnosis was based upon histopathologic findings and/or follow-up of at least 12 months. The sensitivity, specificity, positive and negative predictive values of ERCP tissue sampling combined with IDUS were 90, 93, 93, and 90 percent, respectively.
●In contrast to the above reports, IDUS did not perform as well in another study, especially when compared to cholangioscopic directed percutaneous biopsy (table 7) [31]. The sensitivity, specificity, and accuracy of IDUS for diagnosing cholangiocarcinoma were only 89, 50, and 76 percent, respectively. This compared to a sensitivity, specificity, and accuracy of 93, 100, and 95 percent for percutaneous cholangioscopy. (See "Percutaneous transhepatic cholangioscopy".)
●A prospective study of cholangiography, routine cytology (RC), intraductal biopsy, digital image analysis (DIA), fluorescence in situ hybridization (FISH), and IDUS was performed in 86 patients with indeterminate bile duct strictures of whom 34 had primary sclerosing cholangitis [36]. Overall, 47 patients were found to have malignant strictures. In 80 patients, CA 19-9 results were available as well and a value ≥100 was used as a cutoff for malignancy. IDUS formal criteria as well as the operator's general impression were used to distinguish benign from malignant strictures. Overall accuracy for each of these tests was:
•ERCP – 78 percent
•CA 19-9 – 64 percent
•RC – 50 percent
•Histology – 66 percent
•DIA – 64 percent
•FISH – 70 percent
•IDUS (formal criteria) – 78 percent
•IDUS (endoscopist's general impression) – 90 percent
For patients with negative cytology and histology who were later proven to have malignancy (n = 21), DIA, FISH, composite DIA/FISH, and IDUS lead to a diagnosis of malignancy in 14, 62, 67, and 86 percent, respectively. The authors suggest that IDUS may be most helpful for targeting patients for closer follow-up testing who have concerning features on IDUS, but negative cytology, histology and DIA/FISH.
IDUS may be helpful for directing management even in patients in whom it does not provide a definitive diagnosis [31,37,38]. For example, one group suggested that surgical exploration be performed in patients in whom IDUS identifies disruption of the bile duct wall by a protruding tumor, regardless of the results of tissue sampling [38]. Whereas directed biopsies were recommended when IDUS demonstrates a localized tumor or polypoid lesion in the presence of a normal appearing wall (except for masses greater than 8 mm in diameter, which are likely to be malignant).
Primary sclerosing cholangitis — The role of IDUS in patients with primary sclerosing cholangitis (PSC) is still being determined. IDUS may identify irregular foci within strictures, permitting focused endoscopic transpapillary biopsy [39]. The accuracy of IDUS in diagnosing malignancy in PSC when formal criteria are used is lower than that seen when using an endoscopist's general impression to make the diagnosis (62 versus 82 percent). In addition, the overall accuracy is lower in patients with PSC compared with patients without PSC (62 versus 88 percent) [36].
In experienced hands, IDUS does appear to be useful in PSC. It offers the advantage of allowing for imaging of multiple strictures to identify findings that may suggest malignancy. In one study, it had an accuracy of 82 percent for diagnosing malignancy. Whether these results can be duplicated at other centers and lead to earlier diagnoses of cholangiocarcinoma remains uncertain [37].
Cholangiocarcinoma
Staging — IDUS can improve the accuracy of local tumor staging of bile duct carcinomas (table 8 and table 9 and table 10). IDUS detects early lesions, determines the longitudinal tumor extent, and identifies tumor extension into adjacent organs and major blood vessels with a diagnostic accuracy of nearly 100 percent [7,9,19,40]. In particular, IDUS can accurately identify tumor invasion into the pancreatic parenchyma [8,9,19], portal vein [7,8,19,41], and right hepatic artery [6,8,19,40].
When compared with operative findings, local tumor staging was accurately established in 77 percent of patients with IDUS, but only 54 percent of patients with EUS in one report [13]. The benefit of IDUS over EUS may be even greater for proximal bile duct tumors involving the mid bile duct to the bifurcation. However, the limited depth of penetration of IDUS limits its value for assessing tumor extension outside of the hepatoduodenal ligament and prohibits its use for M-staging [7,42]. The utility of IDUS for N-staging is uncertain and likely to be limited by the inability to perform fine needle aspiration.
Tumor extension — Because bile duct carcinomas spread longitudinally, accurate determination of the extent of spread and the necessary margin of resection is important for planning operative interventions [43-48]. Cholangiography is frequently inaccurate in this setting [10,12].
In one study comparing IDUS to cholangiography, IDUS was significantly more accurate than cholangiography in determining the longitudinal spread of the cancer toward the liver (84 versus 47 percent) and toward the duodenum (96 versus 43 percent) [12]. Similar findings were described in another report in which IDUS accurately determined the proximal extent of tumor invasion in 92 percent of patients [10].
Bile duct wall thickening — Bile duct wall thickening may result from tumor spread or peritumoral inflammation [8-10,37,38,49]. Distinguishing tumor spread from inflammation cannot be reliably done with noninvasive bile duct imaging techniques, including IDUS [8,9,40,50]. However, a number of investigators have described ultrasound criteria that may assist in making this distinction.
A commonly used feature is based upon the observation that inflammation typically causes symmetrical wall thickening, in contrast to cancer infiltration, which typically causes asymmetrical wall thickening [10,12]. However, this criterion has not been a reliable distinguishing feature in all reports [37].
Bile duct stents may also lead to bile duct wall thickening [12,51]. Such stents are frequently required in patients who have biliary obstruction. Biliary decompression following stent placement may lead to thickening of the duct wall and overestimation of longitudinal tumor extension [38,39]. As a result, some authorities suggest that IDUS be performed prior to, or within a few days of, biliary decompression [12].
PANCREATIC INTRADUCTAL ULTRASOUND — Patients with signs and symptoms suggestive of a pancreatic neoplasm typically undergo transabdominal ultrasonography or computed tomography (CT) imaging, which often reveal the presence of a pancreatic mass or fullness. However, uncertainty may remain as to whether the lesion is an inflammatory mass or neoplasm, and whether the lesion is cystic or solid. Furthermore, up to 40 percent of small carcinomas may not be evident with these imaging modalities [52,53].
Additional evaluation using endoscopic procedures such as endoscopic retrograde cholangiopancreatography (ERCP) and/or endoscopic ultrasound (EUS) may be required in these settings. These procedures offer a means to obtain tissue, assist in staging, and provide options for palliative therapy. Increasing experience suggests that IDUS may also be helpful for selected patients [54-59]. (See "Clinical manifestations, diagnosis, and staging of exocrine pancreatic cancer".)
Technique — As with bile duct insertion, the IDUS probe can be placed within the pancreatic duct in almost all patients, usually without the need for prior sphincterotomy [56,60-62]. However, it may be difficult to pass the probe into the proximal pancreatic duct since the pancreatic duct is typically tortuous.
In one series of 153 patients, the IDUS probe could be passed into the pancreatic head, body, and tail in 94, 89, and 55 percent of patients, respectively [13]. In another study, papillary cannulation was possible in 17 of 20 patients (85 percent) [56]. In the three patients where cannulation failed, it was due to the inability to pass the endoscope to the papilla. When cannulation was achieved, the probe could be passed to the head, body and tail in 100, 71, and 35 percent of patients, respectively.
The endosonographic appearance of the main pancreatic duct wall with IDUS varies from a single hyperechoic layer to three layers. When three layers are present, the inner and outer layers are hyperechoic, with an intervening hypoechoic layer [18,56,63]. Visualization of three layers is more likely with use of a 30 MHz (versus a 20 MHz) probe.
Pancreatic IDUS does not appear to add significantly to the risk of standard ERCP with pancreatography. In two studies involving 443 patients, only 4 developed mild pancreatitis [13,54]. (See "Post-endoscopic retrograde cholangiopancreatography (ERCP) pancreatitis".)
Pancreatic duct strictures — IDUS may be useful for determining whether a pancreatic stricture is benign or malignant. In one series, the type of stricture was correctly identified in 23 of 25 patients (92 percent) [39]. Two patients had focal pancreatitis that was incorrectly diagnosed as pancreatic cancer. Another study from the same authors compared the results of IDUS to EUS, CT, and endoscopic retrograde pancreatography (ERP) for determining the cause of localized strictures of the main pancreatic duct [55]. Of the 26 patients enrolled, 14 were ultimately determined to have had pancreatic carcinoma, while 12 had benign strictures from chronic pancreatitis [55]. IDUS was more sensitive than EUS, CT, and ERP (100 versus 93, 64, and 86 percent, respectively) and more specific (92, 58, 67, and 67 percent, respectively).
Pancreatic adenocarcinoma — The utility of IDUS in the evaluation of patients with suspected adenocarcinoma was described in a study involving 239 patients with pancreatic disorders, including 48 with adenocarcinoma [54]. IDUS was more sensitive than EUS, CT, and ERP (100 versus 90, 67, and 90 percent, respectively) and more specific (92 versus 60, 64, and 64, percent, respectively) (table 11). (See "Clinical manifestations, diagnosis, and staging of exocrine pancreatic cancer".)
Mucin producing tumors — Four types of cystic neoplasms of the pancreas have been described (table 12):
●Mucinous cystadenoma/cystadenocarcinoma
●Intraductal papillary mucinous tumor
●Serous cystadenoma
●Solid pseudopapillary neoplasm
Serous cystadenomas are benign, with rare exception, and can generally be managed with observation alone. The other lesions are premalignant or malignant and are generally indications for surgical resection. Correct diagnosis is important since these tumors have a better prognosis than ductal adenocarcinoma. (See "Classification of pancreatic cysts" and "Pancreatic cystic neoplasms: Clinical manifestations, diagnosis, and management".)
Conventional imaging studies, such as transabdominal ultrasound, CT, and MRI, often inadequately characterize and differentiate among the cystic neoplasms [64,65]. This is especially true for lesions less than 2 to 3 cm in diameter, which are often difficult to identify by conventional imaging. The role of EUS and IDUS in the evaluation of these tumors is still being determined. Initial experience suggests that EUS can be helpful and that IDUS may be more accurate than EUS [54,62,66,67].
In one study involving seven patients with mucin-producing tumors involving the main pancreatic duct (picture 3), IDUS identified abnormal areas that corresponded to adenomatous tissue or intraductal carcinoma, but could not distinguish between the two [54]. A mural nodule was identified in 11 of 21 patients with ductal mucin-producing tumors; three patients had carcinoma, seven had adenoma, and one had hyperplasia. Five of these nodules were not visualized by EUS. In the 10 patients in whom IDUS did not reveal a nodular defect, one was found to have an adenoma and the other nine had hyperplasia. Thus, the finding of a mural nodule at IDUS correlated with an increased likelihood of malignant involvement.
IDUS was also useful in evaluating the feasibility of partial pancreatic resection for mucin-producing tumors of the ductal branches and for pancreatic neuroendocrine tumors. Three of 21 patients with adequate distance between the duct and the lesion were able to undergo partial, rather than complete, pancreatic resection. (See 'Pancreatic neuroendocrine tumors' below.)
Another study compared the detection rates of IDUS, transabdominal ultrasound, CT, EUS, and pancreatoscopy (picture 4) in 31 patients with mucin-producing tumors who underwent surgical and pathological confirmation [61]. These included six patients in whom the papillary tumors originated within the main duct and 25 patients in whom the papillary tumors originated within dilated branch ducts. Papillary projections (image 5) were limited to the side branches in 10 of the 25 patients considered to have side branch disease while they also involved the main duct in the other 15 patients.
Surgical specimens revealed that eight patients had mucinous cystadenocarcinoma, 19 had mucinous cystadenoma, and four had hyperplasia. All patients with adenocarcinoma had papillary projections in the pancreatic ducts of 3 mm or greater in height. The detection rate of such lesions was higher for IDUS (100 percent) compared with transabdominal ultrasonography (29 percent), CT (21 percent), EUS (86 percent), and pancreatoscopy (83 percent).
Conclusions — These studies demonstrate that IDUS can detect small lesions and determine the extent of intraductal spread and parenchymal invasion. This information can help determine the necessary extent of resection for mucin-producing tumors involving the main pancreatic duct. IDUS can also help assess the indications and extent of necessary surgery for patients with side-branch disease by identifying papillary tumor projections.
Pancreatic neuroendocrine tumors — Pancreatic neuroendocrine tumors (PNETs) are rare tumors of neuroendocrine origin which usually arise in proximity to the pancreas. The majority are nonfunctional, but many secrete biologically active substances resulting in specific clinical syndromes (ie, insulinoma, glucagonoma, somatostatinoma, VIPoma, gastrinoma) (see "Classification, epidemiology, clinical presentation, localization, and staging of pancreatic neuroendocrine neoplasms", section on 'Classification and nomenclature').
Several imaging modalities are available to assist in localizing the tumors. (See "Classification, epidemiology, clinical presentation, localization, and staging of pancreatic neuroendocrine neoplasms", section on 'Imaging studies for disease localization'.)
Although experience with IDUS is limited, initial data suggest that IDUS may improve the evaluation of these patients and lead to the identification of tumors arising within the pancreas that have gone unrecognized by other techniques [54,58]. In one study, IDUS was able to identify the presence of a PNET in seven of seven patients [54]. In one of these patients with multi-focal disease, IDUS accurately determined the number of tumors, while EUS failed to detect all lesions. In the patients with PNETs, IDUS also accurately determined the distance from the tumors to the main pancreatic duct, thus aiding preoperative planning of wedge resection, which was possible in two patients.
Most PNETs appear sonographically as echo-poor, homogenous, well-delineated lesions. A minority of these tumors appears as echo-rich, inhomogeneous lesions with an irregular outer margin.
PAPILLA OF VATER INTRADUCTAL ULTRASOUND — Intraductal ultrasound (IDUS) accurately visualizes the anatomy of the papilla and is the only procedure that reliably differentiates the sphincter of Oddi musculature from the remainder of the papilla [68,69]. As a result, IDUS can be useful for diagnosing and assessing the size and extent of papillary tumors [70,71].
The ability of IDUS to diagnose tumor extension was evaluated in a prospective study involving 32 patients with cancer of the papilla of Vater who underwent surgical resection [70]. IDUS was performed percutaneously in 24 patients and endoscopically in the other eight. IDUS was able to determine the tumor extent with an accuracy of 88 percent. As expected, because of the limited depth of penetration and inability to perform fine needle aspiration, the sensitivity for determining nodal metastases was only 67 percent, with a specificity of 91 percent. Nevertheless, this compared favorably to transabdominal ultrasonography and computed tomography (CT), which detected only 9 and 6 percent of the tumors, respectively. (See "Ampullary carcinoma: Epidemiology, clinical manifestations, diagnosis and staging".)
In another prospective study involving 27 consecutive patients, IDUS (endoscopically inserted in all patients) was compared to EUS and CT with regard to tumor visualization, diagnosis, and staging [69]. The final diagnosis at surgery was a benign tumor in 12 patients and papillary carcinoma in 15. IDUS was superior to EUS and CT for tumor visualization (100 versus 59 and 30 percent, respectively). IDUS was more sensitive and specific than EUS (100 versus 63, and 75 versus 50 percent, respectively). This study suggests that IDUS may be the most accurate imaging modality for the diagnosis and local staging of tumors of the papilla of Vater.
SUMMARY AND RECOMMENDATIONS
●Intraductal ultrasound (IDUS) is a newer form of ultrasound technology and offers promise in the evaluation of patients with pancreatobiliary disorders. The use of high frequencies allows production of high-resolution images and detailed examination of ductal and periductal tissues. However, the limited depth of penetration prevents examination of more distant sites.
●IDUS can determine the etiology of bile duct strictures and significantly increases the diagnostic accuracy over other imaging studies and/or tissue sampling. As a result, it is becoming an essential part of the work-up of patients with indeterminate strictures in centers where the technology is available. (See 'Bile duct strictures' above.)
●For patients with known malignant bile duct or ampullary strictures, IDUS compares favorably to other imaging modalities with regard to tumor visualization, diagnosis, staging, and predicting resectability. The information obtained from IDUS examinations also helps select appropriate candidates for surgery and often helps the surgeon to select the most appropriate technique. (See 'Cholangiocarcinoma' above and 'Papilla of Vater intraductal ultrasound' above.)
●In patients with pancreatic duct strictures, IDUS can be used to distinguish between benign and malignant pancreatic duct stenosis. (See 'Pancreatic duct strictures' above.)
●For patients with mucinous duct ectasia (intraductal papillary mucinous tumor), IDUS is able to distinguish main duct disease versus side duct disease, and determines the extent of tumor spread and parenchymal invasion. This information can be used to determine the indications and extent of necessary surgery. (See 'Mucin producing tumors' above.)
●For patients with pancreatic neuroendocrine tumors, IDUS can identify otherwise undetected or multifocal tumors. This may lead to improved surgical planning and limit the extent of pancreatic resection. (See 'Pancreatic neuroendocrine tumors' above.)
