2019 Volume 61 Issue 5 Pages 1145-1157
This paper describes technical tips for performing endoscopic ultrasonography (EUS) for invasion depth diagnosis of colorectal T1 carcinomas. EUS is a unique diagnostic modality different from colonoscopy that enables observation of images of cancer invasion to the submucosal layer by obtaining cross-sectional images of the lesion. It is recommended that novice endoscopists perform EUS by using a high-frequency ultrasound probe (HFUP), which is inserted through a standard colonoscope. EUS has some disadvantages including not being able to obtain EUS images in about 10% of lesions and occasionally obtaining unsatisfactory images of lesions located in flexures of the colon or on the colonic haustra. The accuracy of invasion depth diagnosis can be improved with intensive scanning of the suspicious invasive portion of the lesion by colonoscopy and scanning while looking at only the EUS monitor and not the endoscopic monitor. In case of polypoid lesions with a height of 6mm or more, it is difficult to obtain good HFUP images of the deepest part of the lesion by deep attenuation. In such cases, additional use of low-frequency probes (12 or 7.5MHz) is helpful for obtaining satisfactory images. We performed a retrospective review of cases in which EUS was performed for invasion depth diagnosis of colonic lesions in our department between 2007 and 2017. The overall accuracy of invasion depth diagnosis for determining the choice of therapy (i.e., endoscopic resection or surgery) was not very high at 77.0% (211/274). The accuracy of invasion depth diagnosis was significantly higher in T1b carcinomas than in Tis･T1a carcinomas [87.3% (125/151) vs. 69.2% (86/123) respectively; p<0.01]. Moreover, the accuracy rate was significantly higher in flat and depressed-type T1b carcinomas than in polypoid-type T1b carcinomas [91.4% (53/58) vs. 83.3% (50/60), respectively; p<0.05]. We think that HFUP will be useful for invasion depth diagnosis of especially flat and depressed-type T1b carcinomas. Because the submucosal invasion distance measured by EUS images has a good correlation with that measured in histological specimens, EUS will become an essential diagnostic modality in oder to expand the indications for endoscopic resection of T1b carcinomas as total excisional biopsy. Therefore, it is strongly recommended that all endoscopists become familiar with EUS procedures.
