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One major limitation of EUS in staging esophageal neoplasms is the larger diameter of the echoendoscope, which is unable to pass through at least 25% of strictures, even though they may be traversed with thinner endoscopes. Several prototype echoprobes have been designed to attempt to deal with this problem. One type of probe can be inserted through a 3.5-mm biopsy channel of a standard endoscope. Both the accuracy and the utility of this probe is limited by the very small acoustic field of view and the limited penetration of its 20-MHz sound wave frequency [40]. Another approach is based on a blind echoprobe that can be passed over a guide wire through esophageal strictures [41 ]. The diameter required to pass this instrument is less than 9 mm (33 French), compared with the usual 12.6-mm (40 French) diameter of the echoendoscope. This probe may prove useful in patients with apparent advanced disease that cannot be documented by other nonoperative techniques. Its ability to detect celiac nodes not seen on CT would have a significant impact on selection of radiotherapy, endoscopic palliation, or chemotherapy over surgical therapy. In terms of clinical outcome, however, inability to pass the echoendoscope through a stricture may not be significant [15,32,42,43] because (1) stenotic lesions are generally advanced (90% invade through the muscularis propria [T3 or T4] and have spread to many lymph nodes or distant sites); (2) EUS often finds malignant lymph nodes proximal to the stenosis; (3) CT scans will find metastasis to distant sites, which occurs more often in lesions with an advanced T stage (EUS up to the stenosis plus CT scan will provide as accurate an evaluation as EUS past the stricture in more than 95% of patients); and (4) as described, aggressive dilation of these strictures at the same session as EUS is associated with a high risk of perforation and is not recommended [42]. Two studies looked at selective passage of stenotic esophageal tumors [43,44] with and without dilation. No complications were reported. In 1 study [43], EUS was very accurate, both for lesions with stenosis easy to pass through, and for those that could not be traversed (Table 7). EUS was least accurate in staging lesions with stenosis that was "difficult to pass," but EUS accuracy was still better than CT for these difficult-to-pass lesions. In another study, lesions through which a 9-mm endoscope was unable to pass (16%), were not dilated; all patients had T4 disease. In 62% of patients, the echoendoscope passed beyond the stricture without dilation, 21% of patients had tumors that were dilated to allow the echoendoscope to pass. In this latter group, only 2 patients (15%) did not have a T3 or T4 lesion, and 40% had malignant celiac nodes. From this study it appears that dilation can be performed if needed over several sessions in the usual manner without significant complications. Table 7
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