Endoscopic ultrasonography: imaging and beyond
Authors: T Rosch
Journal: Gut (2003)

ndoscopic ultrasonography (EUS), introduced into gastroenterological diagnostics more than 20 years ago, has undergone extensive evaluation of its diagnostic capability, probably to a larger extent than most other endoscopic and other imaging techniques in gastroenterology.Almost necessarily, as to be expected with an imaging method being assessed with continuing interest for two decades, initial enthusiasm has waned and questions about its influence on management and outcome have been dealt with, yielding mixed results.Other imaging techniques are usually not burdened by such a self critical approach, mostly due to the fact that technical progress has hindered proper evaluation, and techniques are marketed with only little good evidence of their real value.Methodological questions about study quality in gastrointestinal imaging have attracted limited interest, and only rarely are factors looked into, which may be responsible for divergent study results. 1 However, it happened a few years ago that EUS was revitalised, mainly due to the advent of EUS guided fine needle aspiration (FNA), 2 and even more recently, several emerging techniques of EUS guided therapy. 3The following does not aim at giving a full overview on the ever rising body of literature on the accuracy of diagnostic EUS, including FNA.For this purpose textbooks and review articles in various journals 2 4 are recommended.Some current trends and possible future tendencies will be outlined. c TECHNICAL FACTORSEchoendoscopes-with some recent exceptions-are oblique viewing endoscopes which carry a rigid ultrasound transducer at their tip, which either generates a 360°round view perpendicular to the shaft axis or a linear image of variable width parallel to the endoscope axis.Radial scanners have been mechanical scanners but recently electronic scanning-the principle of linear scanners-is being developed for radial scanning also.EUS utilises high ultrasound frequencies (5-20 MHz, 7.5 MHz being the most frequently used ultrasound frequency) which generate a high resolution image in the near field with limited penetration depth, ranging from 1-2 to 5-6 cm, depending of the ultrasound frequency used.EUS is usually done with the patient in the left lateral position, mostly under conscious sedation, and is associated with very low complication rates 5 with very few exceptions. 6Details of the examination technique for the various organs in focusgastrointestinal tract and immediate surroundings, mainly the pancreatobiliary tract-are described elsewhere. 7 8Miniprobes are a further development which mirror the miniaturisation of the technique (they are referred to below).Linear echoendoscopes are necessary for the performance of EUS guided FNA as only with these instruments can the course of the puncture needle be followed.An average of 2-4 passes is necessary to obtain adequate tissue for cytological smears, and the presence of an in-room cytopathologist seems to improve the yield 5 ; some examiners try to obtain small core specimens for histopathological analysis but the relative yield and accuracy of cytological and histological analysis, as well as the best needle diameter (19 or 22 gauge), are still unclear. ENDOSONOGRAPHIC IMAGING: TUMOUR STAGING STILL THE MAIN INDICATION?After primary diagnosis of gastrointestinal malignancies by endoscopy and biopsy, EUS is used secondarily for locoregional tumour staging; this applies to oesophageal, gastric, and rectal cancer as well as to gastric lymphoma 9-11 (figs 1, 2); the value of EUS in suprarectal colonic cancer has not yet been established.The use of EUS is limited to patients in whom surgery is considered, either primarily or after neoadjuvant therapy, as EUS is not believed to be useful in inoperable patients or in those with known unresectable disease or distant metastases.The value of EUS in restaging after such neoadjuvant treatment has been burdened with poor results 12 but more elaborate assessment methods such as two dimensional 13 or even three dimensional volume measurement may fare better.In gastric lymphoma, EUS is clinically useful in selecting patients for Helocobactor pylori eradication treatment, 14 15 and restaging after chemotherapy seems to be more successful than in upper gastrointestinal cancer 16