The Pulse | Thursday, January 27, 2022
Endoscopic Ultrasound: The Frontier in GI
Since its inception in the early 1980s, endoscopic ultrasound (EUS) has evolved from a rarely available experimental endoscopic commodity to a powerfully evolved endoscopic tool indispensable to a comprehensive gastroenterology practice. Furthermore, the indications and uses of EUS continue to expand exponentially. In fact, when one looks at where the majority of pioneering new endoscopic techniques and maneuvers are occurring in the field of gastroenterology over the past several years, they would find that EUS lies in the heart of this progress. Thus, it is essential for all gastroenterology health care providers to be familiar with the basics of EUS and have a good understanding of where its utility can be of best use for their patients.
Ultrasonography uses sound waves as a mechanical form of energy that is transmitted as a wave through fluid or solid medium and reflected back to the transducer, producing an image. The appearance of the image will vary based on the density of the target structure.
EUS is a technological fusion of both flexible fiberoptic endoscopy and ultrasonography. By affixing a specially designed ultrasound probe to the tip of an endoscope, higher quality imaging of internal body structures can be obtained, circumventing the interference and degradation of imaging that comes with transcutaneous views. The imaging via EUS is acquired in real time, and the operator has full maneuverability to direct the imaging, as well as focus and enhance it, on a target structure of their choice. There are two main types of echoendoscopes, radial array and linear array echoendoscopes that differ in the plane in which imaging is acquired.
The utility of EUS has evolved rapidly over the years. The main and initial usage of EUS was for locoregional staging of luminal GI cancers, such as esophageal, gastric, pancreatic or rectal cancer. High frequency EUS probes are able to differentiate the different layers of the GI lumen to help determine tumor depth, a key factor in oncologic staging. More importantly over the years, tissue acquisition has become one of the major indications for EUS. Using either a fine needle (FNA or Fine Needle Aspiration) or a core biopsy needle (FNB or Fine Needle Biopsy) structures deep to the superficial mucosal layer of the GI tract are able to be sampled for diagnosis. Pancreatic cancer, for example, is now considered a first line indication for EUS tissue biopsy.
There are several different needle types and sizes available, and a variety of different techniques available to maximize the yield of FNA, such as using on-site pathology services to provide real-time feedback on the samples obtained. It is important for GI nurses and technicians working in endosonography to be familiar with the different needle types and methods of tissue acquisition and processing, as this has large implications on the quality of specimen obtained.
An important use for EUS is the characterization and surveillance of pancreatic cysts and cystic neoplasms, which are increasing in frequency and serve as a precursor to pancreatic cancer. Other uses for EUS include ruling out bile duct stones and targeted fiducial placement to aid in image guided radiation therapy.
As experience with EUS has increased and dedicated device and technology enhancements have evolved, due in large part to collaboration within the industry, the indications for EUS have expanded into exciting new avenues. The field of therapeutic EUS is an exciting arena for gastroenterologists and GI providers worldwide. A great example of therapeutic EUS is the endoscopic management of pancreatic pseudocysts, a condition which once required lengthy endoscopic techniques or highly morbid interventional radiology and surgery involvement. Pseudocyst drainage can now be done under EUS guidance in less than 15 minutes with excellent clinical results and is now considered first line therapy.
Another example of therapeutic EUS includes transgastric or transduodenal EUS-guided gallbladder drainage for patients with cholecystitis who are not operable candidates. EUS is being used for access to the biliary tree when traditional ERCP is not possible, such is patients with altered surgical anatomy or inaccessible ampullas. EUS guided gastrojejunostomy is an exciting new indication that involves using an EUS to perform a luminal bypass for patients with gastric outlet obstruction.
Gastric variceal embolization is also being performed via EUS in specialized centers, helping manage an otherwise deadly disease that has been difficult to treat. Finally, EUS-guided injections of ablative agents or chemotherapeutics have been used for pain control (celiac plexus blocks) and local tumor palliation (in experimental trials).
In the end, EUS has proven to be an indispensable tool for the comprehensive GI practice, with ever-evolving techniques and indications putting it on the forefront of exciting GI innovation and making it an essential tool and a skillset for GI healthcare providers to become familiar with and excel.
- Varadarajulu S., Wallace MB. Applications of endoscopic ultrasonography in pancreatic cancer. Cancer Control 2004; 11:15-22.
- Wang J., Endoscopic ultrasound guided fine needle aspiration versus endoscopic ultrasound guided fine needle biopsy in sampling pancreatic masses: A meta-analysis. Medicine (Baltimore). 2017; 96:e7452
- Rimbaş, M., A. Larghi and G. Costamagna. Endoscopic Ultrasound 6 (2017): 235-240.