Comments on New Technology - Endoscopic ultrasonography (EUS) Routine method and new applications

Table of Contents

Jan Janssen and Lucas Greiner

EUS started in the early 1980s with radial mechanical scanners causing an imaging revolution. For the first time, the visualization of the gastrointestinal wall layers became possible and thus improved the locoregional staging of gastrointestinal tumors. Nearly at the same time, the method was extended to biliopancreatic disease and further clinical applications.

The second revolution in connection with EUS was the introduction of longitudinal electronic scanners in the 1990s enabling and establishing fine-needle aspiration biopsy (FNAB) under realtime EUS control. Electronic scanners have significantly improved the spatial resolution and the quality of imaging within the near field. Therefore, this technology is nowadays also implemented in radial scanners. EUS guided FNAB allows to obtain histologic specimen from the surroundings of the gastrointestinal (GI) tract. Furthermore, FNAB proved to be the first step towards EUS guided interventions like injection treatment (e.g. neurolysis of the celiac plexus) or drainage of pancreatic pseudocysts.

In the meantime, many indications for the use of diagnostic and interventional EUS have been investigated and the reader may be interested to know which of them are currently accepted or have been dropped. The second focus may concern new EUS developments.

Current applications of EUS

Before endoscopic mucosal or submucosal dissection of early gastrointestinal wall tumors, EUS is accepted to be the best non-invasive method to predict the stage and resectability of the lesion. Although one can argue that the pathologist is the one to definitely define the infiltration depth, it is favourable to know the EUS result beforehand especially with respect to the potential involvement of regional lymph nodes.

Neoadjuvant treatment for locally advanced cancer has to be based on the thorough description of the tumor stage. This treatment policy nowadays is standard for stage T3/4 tumors of the esophagus and rectum which are usually defined by EUS. In esophageal cancer, the involvement of celiac lymph nodes is no longer regarded to be crucial to decide about resectability and, therefore, EUS-FNAB of these lymph nodes has become less important.

The new efforts to improve the cure rate of locally advanced gastric tumors - especially of the cardia - by neoadjuvant chemotherapy has resulted in the revival of EUS for the staging of gastric cancer (although laparoscopy might be very useful in this setting, too). The choice of treatment in gastric lymphoma (MALTOM) depends on the degree of malignancy and in low grade lymphoma on the local spread. Therefore, EUS is mandatory in the staging of gastric lymphoma.

After neoadjuvant treatment (chemotherapy alone or radiochemotherapy), the question of tumor regression or even disappearance is of interest. In this respect EUS fails, because the echopoor inflammatory reaction caused by these modalities cannot be differentiated from tumor infiltration and, hence, the diagnostic accuracy proved not to surpass 50-60 %.

There is no doubt that EUS is the method of choice to differentiate between submucosal GI tumors and external impressions. Furthermore, the echogeneity of submucosal lesions and the determination of their layer of origin significantly helps to determine the therapeutic needs and approach. Endoscopic resection can be done with low complication rate, if the lesion is located superficially to the proper muscle layer.

Pancreatic tumors are a further target of EUS which is able to reveal very small lesions in otherwise healthy organs. The ability is of clinical value looking for endocrine tumors that are suspected due to their endocrine activity. The early detection of ductal carcinomas will usually fail, since EUS is no screening method. The staging of pancreatic tumors can be helpful, although data as to the prediction of vessel infiltration are conflicting. EUS-FNAB can reliably be performed to define pancreatic lesions histo- or cytologically. Like all competitve diagnostic methods, EUS even in addition with elastography or FNAB is not suitable to detect early stage pancreatic cancer in chronic pancreatitis.

Studies have shown that EUS is a valuable tool to diagnose early pancreatitis before ERC criteria become visible. The diagnostic accuracy for biliary stones or other reasons of biliary obstruction is at least as good as on ERCP. Therefore, diagnostic ERCP, which is affected by more and potentially severe complications, is nowadays substituted by EUS. MRCP might be an even less invasive alternative. Although the spatial resolution of MRCP is inferior, most comparative studies estimate MRCP and EUS to be equivalent. Therefore, the choice of method may depend on the local setting.

The endosonographic access to the left adrenal is very comfortable and FNAB with the question of M1 metastasis can be reliably performed, if necessary.

EUS guided interventions and perspectives

EUS guided interventions are well established for the drainage of pseudocysts or abscesses. In EUS centers, the drainage of dilated hepatic ducts into the GI tract is performed with promising success rates. Celiac plexus neurolysis can easily be performed, but the sustainability of the procedure is insufficient for pain in the course of chronic pancreatitis and still in discussion for pain caused by tumorous infiltration. Several efforts to treat tumors by EUS guided injection have been made, but they have not yet overcome the experimental stage. Interesting studies in porcine models have tested surgical techniques like EUS guided gastroenterostomy or fundoplicatio.

New non-invasive technologies implemented in EUS are elastography, which is described in EFSUMB Newsletter issue 3 this year, and contrast enhanced EUS which is becoming available in the near future.

Conclusion

In summary, EUS combining imaging (Fig. [1]) and the options of FNAB and intervention (Fig. [2]) nowadays is a valuable and indispensable diagnostic and therapeutic tool in gastroenterology and associated fields. New EUS technologies promise to expand or specify the panel of applications.

Fig. 1 EUS imaging of the normal left adrenal.

Fig. 2a,b Process (a) and result (b) of EUS guided drainage of a pancreatic pseudosyst

Jan Janssen and Lucas Greiner

Medizinische Klinik 2, HELIOS Klinikum Wuppertal

Heusnerstrasse 40, D-42283 Wuppertal

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