Recent studies have shown that if the targets were properly selected, endoscopic resection of early esophageal cancer results in a 5-year survival rate of 98% and low recurrence rate. According to a meta-analysis, the pooled diagnostic sensitivity and specificity of EUS for T1 stage were 86.1% and 99.4%, respectively.5 Among T1 cancer, mucosal esophageal cancer is subclassified into M1, M2, and M3, which respectively correspond to the cancer invasion of the epithelium, lamina propria, and muscularis mucosa. M1 and M2 cancers are the can-didates for endoscopic resection with no risk of lymph node metastasis. High frequency miniprobe demonstrates well defined nine-layered structure of esophageal wall, which is in good correspondence with histological layers and provides high accuracy in decision making process for the selection of treatment options of early esophageal cancer. Shimoyama et al.6 performed EUS with 12 to 20 MHz miniprobes for T staging and they were able to select correctly all candidates of endoscopic therapy. But there are also other conflicting studies insisting EUS does not appear to be sufficiently accurate in T staging.7 To reach a definite conclusion, further studies with larger numbers of patients using adequate instrument and long term follow-up results would be necessary since most of the reports have small patient populations and used various low- and high-resolution instruments.

EUS provides higher accuracy of gastric cancer staging compared to that of computed tomography (CT). Accuracy of CT in T and N staging of gastric cancer were 76% and 70%, respectively, but those of EUS were 86% and 90%.8 EUS is also a reliable method for evaluation of depth of gastric cancer invasion and can assist in selection of correct indication for endoscopic resection. One study from Korea has shown high accuracy of high-frequency catheter probe EUS in diagnosis of mucosal gastric cancer which was suitable for endoscopic submucosal dissection reporting 97.6% of diagnostic accuracy.9 Main causes of over-staging or under-staging with EUS are ulcer, edema, fibrosis, inflammation, and microinvasion. It is also noted that cancers located in the upper third of the stomach, depressed morphology, and the size of larger than 3 cm show lower diagnostic accuracy on EUS.10 As a result, the diagnostic accuracy of EUS for T staging of early gastric cancer is reported a wide range of 63% to 95% by different investigators with different experience.

For staging superficial rectal tumors, EUS has demonstrated accuracy rates ranging from 69% to 97%. The diagnostic accuracy of EUS T staging depends on many factors, such as operator's experience, tumor stenosis, postbiopsy peritumoral inflammation, hemorrhage, villous, or pedunculated tumors.11 According to a meta-analysis, pooled sensitivity of EUS in diagnosing mucosal rectal cancer was 97.3% and pooled specificity was 96.3%.12 Authors recommended that EUS should be strongly considered for staging of early rectal cancers to select proper indication of endoscopic treatment.

CE-EUS is composed of two main categories; CE power-Doppler EUS (CED-EUS) and CE harmonic EUS (CEH-EUS). After injection of contrast materials, increased intensity of week flow signal can be examined with color or power Doppler. Therefore, by using CED-EUS, differentiation of vascular-rich area and hypovascular area is possible with clarity. After development of harmonic imaging method, it is possible to get images of microcirculation and parenchymal perfusion with CEH-EUS. The use of CE-EUS allows a better visualization and differentiation of hypoenhanced mass suggestive of pancreatic adenocarcinoma and a hyperenhanced lesion which indicates an inflammatory mass.13,14

Tissue elastic imaging represents a technique that allows cal-culation and visualization of the hardness of tissue. Real-time tissue elastography with ultrasonographic approach is combined to EUS. With this technique, the real-time visualization of the calculated strain value can provide information on tissue hardness at the area of interest and the distribution pattern of tissue hardness as well. In addition to EUS image, these information can guide to select the most probable malignant lymph node to approach for EUS-FNA.15,16

EUS-FNA is now indispensable procedure in both diagnosis and treatment of gastrointestinal diseases. Recently forward viewing convex echoendoscope has been developed to overcome the limitations of conventional oblique viewing echoendoscope. Kida et al.17 reported that even though imaging field is narrower, image quality and penetration of forward viewing echoendoscope is nearly the same as those of conventional oblique viewing echoendoscopes. He also reported that it was easier to perform EUS-FNA with forward viewing echoendoscope compared to oblique viewing echoendoscope.17 For therapeutic approach, usage of forward viewing echoendoscope was better with easy pass through gastrointestinal wall.18