EDITORIAL

 

Endoscopic ultrasonography - an established technique with a brilliant future

Ultrasonografía endoscópica: una técnica consolidada con un brillante futuro

 

 

E. Vázquez-Sequeiros

Service of Gastroenterology. University Hospital Ramón y Cajal. Madrid, Spain

 

 

Endoscopic ultrasonography (EUS) or echoendoscopy is an imaging technique that emerged over two decades ago, during the previous era of computerized axial tomography (CAT), for improved pancreas examination (1-3). The high resolution of images provided by conventional echoendoscopes has rendered EUS a preferred technique for the study of digestive tumors (1-3). Current tumor diagnostic and staging protocols in most third-level hospitals within our healthcare system include EUS (1-3). Malignancies arising in the esophagus, stomach, rectum, and most particularly the pancreas and bile ducts represent some of the better established indications for EUS. The launch of linear puncture echoendoscopes (EUS-FNP) during the early 1990s was of paramount importance, and brought about new indications for EUS (4). In this issue, two excellent papers on echoendoscopy deserve to be highlighted (5,6).

Iglesias et al. (5) provide a detailed, critical review on the current role of EUS and EUS-FNP in the diagnosis and staging of pancreas cancer, and reach three key conclusions that are discussed below.

Conclusion 1. "EUS is the diagnostic technique of choice for patients suspected of having a pancreatic tumor". Most authors agree with this appraisal, which is reflected in the literature (helical CT vs. EUS: 98 vs. 77%, p < 0.0001) (7,8). That is, in patients with clinical suspicion of pancreatic cancer and a negative CT scan echoendoscopy would be necessary to exclude malignancy. The superiority of EUS over CAT and MRI is based on the former technique's higher resolution and sensitivity for the diagnosis of tumors < 2 cm (CAT vs. MRI vs. EUS: 40, 33, 90%) (9).

Conclusion 2. "The accuracy of EUS for the staging of pancreas cancer (70-90%) is equal to or higher than that of other imaging modalities". This statement is more controversial. A systematic review by DeWitt (11 prospective studies, 678 patients) concludes that EUS is superior to multicut helicoidal CT in assessing local/regional tumor extent and splenoportal axis involvement (10). This review found no significant differences in accuracy regarding node staging or overall vascular involvement (including arterial involvement). As a general rule, a pancreatic tumor is usually considered irresectable in the presence of distant metastases or local infiltration of arteries (celiac trunk, hepatic artery, superior mesenteric artery) or veins (extensive infiltration of portal vein or superior mesenteric vein). However, this "theoretical cutoff point" cannot be established so easily in real life. Not uncommonly, a tumor not infiltrating vascular planes cannot be resected during surgery because of a surrounding severe desmoplastic/inflammatory response that prevents tumor-vessel separation. Surgical team experience in this type of procedure and revascularization techniques will greatly determine tumor resectability. From a practical standpoint, establishing whether a pancreatic tumor is surgically resectable is an extremely complicated task, even during surgery. Providing surgeons with all sorts of available imaging data (including EUS data) before the procedure should help make the most appropriate decision for each patient. Unfortunately, no single technique alone can ensure resectability.

Conclusion 3. "EUS-FNP has a high diagnostic accuracy (> 90%) and reduced complication rate (< 1%) for pancreas cancer". While EUS-FNP has a high yield in this patient population (11), not all authors endorse the same indications. In our view, EUS-FNP should only be used for pancreatic masses when findings may modify patient management. Clinical settings where the use of EUS-FNP may be advocated for include: a) suspicion of tumor histology other than pancreatic ductal adenocarcinoma (lymphoma, neuroendocrine tumor, metastases from other tumors), because of therapeutic and/or prognostic implications may vary; b) irresectable pancreatic tumor according to imaging techniques (not eligible for surgical resection, eligible for chemotherapy); and c) patients with uncertain resectability who will be offered neoadjuvant therapy before the procedure (12). In our opinion a biopsy cannot be warranted for pancreatic lesions consistent with ductal adenocarcinoma that appear to be resectable on imaging tests, since puncture findings (either positive or negative) will not change patient management (attempt at surgical resection), and patients would thus be exposed to unnecessary risks (12).

On the other hand, we should bear in mind that EUS has evolved since inception to become a major therapeutic tool. The ability to perform EUS-FNP with therapeutic linear echoendoscopes fitted with working channels has favored the development of various EUS-guided therapies: celiac plexus neurolysis, pancreatic pseudocyst and perirectal abscess drainage, pancreas and bile-duct puncturing and drainage for tumor palliation, brachytherapy seed implants, etc. (13). Experience in this field is still limited (not available in all centers), and both efficacy and safety are usually poorly understood. This fact has awakened a growing interest in research using animal models to validate the effectiveness and safety of such therapies. A clear example is the original paper by López-Martín et al. (6). The authors of this study follow the line of investigation opened by Fritscher Ravens (14), and used an animal model to investigate the feasibility of accessing heart chambers using transesophageal EUS-FNP, as well as the procedure's side effects on the heart (arrhythmia, bleeding, etc.). While the study recruited a small number of animals, the authors are first to demonstrate that right heart chambers can be accessed through the interatrial septum with no evidence of complications. However, potential therapies via this novel approach remain to be demonstrated. In our view, the great merit of this study lies in the fact that this is the first report in our setting where an animal model is used for echoendoscopical research. Such pioneering studies in our field open new lines of research into the interesting arena of therapeutic echoendoscopy. The expansion of echoendoscopical research and its use in animal models show that EUS enjoys perfect health in our setting, and that some of the existing teams are highly qualified in this area.

In summary, EUS is a clearly established technique in our healthcare system, and is usually included within the preoperative algorithm for most digestive tumors, among which pancreas carcinoma remains outstanding. The relevant role of EUS in tumor identification, loco-regional spread assessment, and biopsy collection is widely endorsed by the scientific community. The huge expansion witnessed in the last few years regarding the field of EUS-guided therapy requires prior trials using animal models. The publication in our setting of the first three papers on therapeutic echoendoscopy in animal models is praiseworthy indeed, and a reflection of the perfect health enjoyed by echoendoscopy at present.

 

References

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