Linear endo-ultrasonographic signs of muscularis propria invasion in early rectal cancer

Background and study aim Local resection of early rectal cancer is being increasingly used. With invasion of the muscularis propria layer of the rectal wall, the risk of lymph node metastasis becomes too high to consider this the optimal oncological treatment. Therefore, a diagnosis of muscular invasion is important before attempting local resection; however endoscopic and MRI images have limitations such as overstaging (26–31%). We investigated the potential of linear endoscopic ultrasound (L-EUS) in the diagnosis of muscularis propria invasion. Patients and Methods The study consisted of a development phase, in which linear (L-) EUS features, associated with muscular wall invasion were searched and tested, and a validation phase, during which 30 representative videos were assessed by the author FtB and four experienced endosonographists without experience in rectal L-EUS. Results The development cohort consisted of 91 patients (2019–2023). Six EUS features were found to be significantly associated with muscular wall invasion: tornado sign, blob sign, massive connection, layer split, extramural deposit and, most importantly impaired shiftability between the lesion and muscularis propria layer. During the development phase, these findings demonstrated excellent diagnostic features (sensitivity, 94.4%; specificity, 97.9%; and overstaging, 4%). In the validation phase, the sensitivity, specificity, and overstaging by FtB were 88%, 85%, and 12%, respectively. Among the four inexperienced reviewers, the percentages were 65–71%, 46–54%, and 33–39%. When considering the 27 videos that were considered easy or moderately difficult to assess, only 55% were correctly interpreted by the inexperienced reviewers. Conclusion Linear endoscopic ultrasonography may be a valuable tool for the assessment of ingrowth into the muscularis propria in supposedly early rectal cancer, especially using its dynamic potential to assess fixation to the muscular wall by moving the lesion. However, training was required to achieve satisfactory results.