Introduction  

EUS has come a long way in twenty or so years since its first description. Once the preserve of a dedicated and 'lucky' few, working in the rarefied atmosphere of academic centers, many gastroenterologists regarded EUS as esoteric and unlikely to last the course. Nowadays even the most skeptical accept that EUS is here to stay, and it has now earned its place in mainstream endoscopy throughout the world. While not everything relating to EUS is black and white yet, the shades of gray are certainly becoming clearer.

 History   

EUS began in the early 1980s with rather cumbersome and unwieldy mechanical radial instruments, with which pioneers developed the technique, defining anatomy and correlating images with CT, intraoperative findings, and results of surgical pathology. Artefacts and pitfalls of imaging were carefully studied and image quality improved dramatically with new transducers and a greater range of scanning frequencies. This progress was matched by parallel improvements in endoscopic optics and scope handling characteristics. At the same time as Olympus were refining radial mechanical instruments, Hitachi/Pentax developed the first curved linear array (CLA) echoendoscope. This instrument introduced electronic transducers to EUS, allowing color Doppler imaging and subsequently the ability to perform real-time EUS-guided tissue acquisition by fine-needle aspiration cytology.

Steady progress in research and development has now led to a considerable range of instruments capable of providing exquisite high-resolution images in a wide range of clinical settings. As well as mechanical radial instruments there are high-quality CLA echoendoscopes with large operating channels which allow therapeutic procedures, through-the-scope catheter probes imaging at up to 30 MHz, and, most recently, electronic radial instruments, the latest models of which allow 360° imaging. With parallel advances in ultrasound processors the capabilities and potential of EUS continue to grow, with modalities such as tissue harmonics, contrast enhancement agents, and elastography yet to be fully explored.

 Current applications   

Cancer staging remains the workhorse of EUS. While advances in multi-detector CT scanning and MRI may diminish much of the current superiority of EUS for locoregional (T, N) tumour staging, EUS retains a key role in staging cancers of the esophagus, stomach, pancreas and rectum. Outwith the gastrointestinal tract perhaps one of the most clearcut and least controversial roles of EUS is in the mediastinal staging of non-small cell lung cancer and the evaluation of posterior mediastinal masses. EUS is invaluable in the assessment of submucosal lesions, thickened gastric folds, and a variety of benign disorders, including choledocholithiasis, microlithiasis, and chronic pancreatitis. Perhaps, however, the importance of EUS has been cemented by its ability to provide high-quality tissue samples of excellent diagnostic accuracy and relative safety. This is especially true in situations such as small lymph nodes undetected by other means and in lesions inaccessible by other routes. The recent development of core biopsy needles is another exciting step forward, allowing detailed immunohistochemical and molecular studies to be performed on tissue samples. EUS is ideally placed to play a key role in this translational research, combining the power of microarray and proteomic technology with the ability to obtain tissue samples from otherwise often inaccessible targets.

 Therapeutic EUS   

Although EUS is still thought of as relatively new, it has grown into a mature technology, yet the goal of truly therapeutic EUS seems to have been a long time coming. Celiac plexus neurolysis is simple and well established and the place of EUS in drainage of pancreatic pseudocysts is increasingly clear. As for other procedures, case reports and small case series have allowed us a glimpse of the future but large studies of the efficacy and safety of EUS-guided procedures such as tumor ablation, delivery of antitumor agents, biliary drainage, and creation of anastomoses are still awaited. Surely their time will come in the near future?

 Teaching and training EUS  

The learning curve is steep, training is long, demand is finite, and equipment is expensive. It is likely, therefore, that for the foreseeable future EUS will remain largely within the realm of academic or regional centers. Whether or not all gastroenterology trainees should undertake EUS is a difficult question. If only some are to be trained, should it be those with an interest in pancreatico-biliary endoscopy, those with an interest in gastrointestinal cancer, or others? Indeed, should we just train gastroenterology fellows? In some countries EUS is performed routinely by gastrointestinal surgeons or radiologists. What should constitute a training curriculum for EUS is another issue yet to be satisfactorily resolved. What is clear is the ongoing need for high-quality training in EUS, as this procedure is here to stay, will continue to evolve, and is likely to remain an integral part of gastrointestinal endoscopy for many years to come.

The chapters in this volume address EUS instrumentation and technique, the principles of EUS cancer staging, the role of EUS in evaluating submucosal tumors, lung cancer, and mediastinal masses, and, finally, benign and malignant pancreatic or biliary disease. They are written by some of the most respected experts in this field and provide detailed up-to-date and state-of-the art reviews which I hope you find informative and enjoyable.

Copyright © Blackwell Publishing, 2005