Emerging indications for EUS

Abstract

VOLUME 52, NO. 6 (Suppl), 2000 GASTROINTESTINAL ENDOSCOPY S55 The continued relevance of EUS will require innovation and new applications. Previously important implications for EUS such as cancer staging and the evaluation of submucosal tumors are being challenged by less invasive imaging methods. Innovations in high-resolution imaging, improved tissue acquisition, and EUS-guided therapy will likely provide new indications for EUS. Emerging indications for EUS include improvements in diagnostic EUS and advances in therapeutic EUS. Although there are extensive publications on the accuracy of EUS for cancer staging, there remains a paucity of information on the effect of EUS staging on outcomes such as patient survival, global health care cost, and quality of life. Areas of experimentation in EUS for cancer staging include assessing response to chemoradiotherapy and the effect of EUS-guided management changes on patient outcomes. The ability of EUS to stage small tumors appropriate for endoscopic resection and to identify invasive tumors in patients with Barrett’s esophagus-associated dysplasia continues to undergo clinical investigation. Previous studies with 7 to 12 MHz instruments demonstrated EUS to be insensitive to early tumors. New EUS technology such as 20 to 30 MHz probes and spiral (threedimensional) EUS is currently being evaluated. EUS-directed anti-tumor therapy including the injection of biologic toxins, gene therapy, brachytherapy, and radiofrequency ablation are all promising experimental methods in preclinical and clinical development. Complete cystenterostomy for large symptomatic pseudocysts is an area of active experimentation with the advent of large-channel echoendoscopes. These devices will likely open a much larger field of therapeutic procedures such as direct gastroenterostomy and biliary-enteric anastomosis for enteral and biliary obstructions due to tumors. EUS is evolving from a strictly diagnostic technique to an image-directed therapeutic technique. Less invasive and less expensive methods of obtaining images of the human body will inevitably supplant more invasive methods. Spiral CT, magnetic resonance cholangiopancreatography, and virtual colonoscopy already compete with their endoscopic corollary for accuracy, without requiring patients to undergo the discomfort of endoscopic intubation. What will the role of EUS be in the coming decades? What experimental indications will become standard indications? The answers to these questions are based on the fundamental properties of EUS. EUS differs from all noninvasive imaging modalities in that it acquires images from within the intestinal tract. The GI tract provides the only natural, large capacity, and safe access to the inside of the human body. By placing US transducers inside the body, much higher frequencies and thus much higher image resolution are feasible. The ability of EUS to couple this high-resolution imaging with real-time tissue sampling by means of fine-needle aspiration (FNA) has been a major advancement for medical imaging. Tumors of the pancreas and lymph nodes have become primary indications for EUS-guided FNA. The use of EUS-FNA for the diagnosis of mass lesions of the adrenal gland, liver, lung, and pelvis are increasingly being reported. EUS-FNA to diagnose benign disorders such as sarcoidosis, chronic pancreatitis, and cystic lesions of the pancreas may further expand the repertoire of clinically useful indications for EUS. EUS has been used as a method for assessing response to chemoradiotherapy in patients with carcinoma of the esophagus or lung. Traditionally, EUS has played a limited role in tumor restaging because it has poor accuracy for distinguishing residual tumor from inflammatory or necrotic tissue. EUSFNA performed before and after chemotherapy in patients with locally advanced disease may identify those patients who may benefit from further therapy. The introduction of very high-frequency EUS catheters (>20 MHz) may allow identification of invasive carcinomas in patients with Barrett’s associated high-grade dysplasia. This technique may identify candidates for a particular therapy such as photodynamic therapy or esophagectomy. EUS-guided pancreatic cancer therapy under clinical investigation includes radiofrequency ablation, injection of cytotoxins, and placement of radioactive seed implants (brachytherapy). From Medical University of South Carolina, Charleston, South Carolina.