EUS is unlikely to provide additional information for patients with large tumors, because the EUS probe cannot always be brought close enough to the lesion to bring its margins into optimum focus. Diagnosis with fine-needle biopsy followed by palliative bypass of the biliary obstruction with endoprosthesis or surgical bypass is straightforward. These patients can then be treated with combined modality therapy.

For tumors that appear localized and are less than 5 cm on standard US or CT scan, EUS will provide the information required to select the most appropriate management plan. Performing EUS early in the evaluation of such patients is likely to be effective in terms of clinical utility. Reviewing the data from various studies shows that endoscopic US will significantly change the management in approximately one third of patients when used in the appropriate clinical setting. If EUS shows the tumor is resectable, then laparoscopy to exclude small liver metastases, generally not seen on CT, may prove to be beneficial prior to attempted resection.

EUS detects vascular involvement by pancreatic tumors as accurately as angiography and is unsurpassed in accuracy of determining resectability [80,86,87]. Because of the high accuracy of EUS in predicting resectability, EUS will be important in directing patients to alternative treatment to surgery. Patients with pancreatic carcinomas that are unresectable due to local invasion of blood vessels (T3) have been shown to respond to combined chemotherapy and radiotherapy. Median survival with combined chemotherapy and radiotherapy matches survival of a contemporary group of less advanced TI tumors resected without combined chemotherapy and radiotherapy [9]. For patients with T3 tumors responding to combined chemotherapy and radiotherapy, in whom surgery is being considered because of CT-demonstrated downstaging, EUS found an additional 40% still unresectable [8]. EUS can assist in evaluating response to combined chemotherapy and radiotherapy and predict resection status of pancreatic tumors. As shown in the algorithm, EUS may also have a role in monitoring patients treated with chemotherapy and radiotherapy.

EUS can detect and stage small pancreatic tumors of all types, including endocrine tumors, even those not localized by other tests [88]. EUS accuracy in detection of endocrine tumors is more than 85%, as compared with less than 50% for angiography, CT, or ultrasound [88-90]. Without EUS, endocrine tumor localization will fail in more than 50% of patients, even when adding MRI, angiography, and venous sampling. Intraoperative US is more complex and is unlikely to show any significant advantage over preoperative EUS, although no comparative study has yet been reported. Because of its accuracy, convenience, and low complication rate, EUS appears likely to replace all other tests as the initial method to evaluate patients diagnosed on clinical signs and laboratory tests as having an endocrine tumor. Localizing duodenal wall gastrinomas is a limitation of EUS. Intraoperative transillumination of the duodenum has been shown to be useful for detection of extrapancreatic endocrine tumors [91].

As with primary pancreatic tumors, EUS has been demonstrated to be highly accurate in staging gallbladder, bile duct, and ampullary tumors [1, 15,92-96]. Until an ampullary malignancy causes changes in the underlining wall layers, EUS cannot differentiate early carcinomas from adenomas. EUS, however, will identify such a lesion as a cause of duct dilation or related symptoms. Inflammatory changes can cause problems in diagnosis and staging, similar to problems with diagnosing and staging lesions in other parts of the GI tract. Biliary tract tumors present a problem for N-stage evaluation with EUS because most lesions, even in the early stage, have associated inflammatory nodes. This factor results in a high false-positive rate for malignant lymph node identification. T-stage accuracy for EUS is 85% for ampullary and biliary tumors and 80% for gallbladder neoplasms. EUS N-stage accuracy is 75% for ampullary tumors and 90% for gallbladder tumors but only 55% for biliary tumors. However, for US and CT, staging accuracy is far less, because these tests merely detect the tumor in 20 to 50% of patients and do not further characterize the lesion.

Small probes can be used to obtain intraductal images. Their clinical utility has not been demonstrated [21, 97,98]. As these probes improve, their role in evaluation of the biliary duct system should expand. For the pancreatic duct system, these probes will probably not be clinically useful.

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