Endorectal ultrasound (ERUS) is considered the technique of choice for selecting patients for transanal endoscopic surgery (TEM). The aim of this study was to evaluate the accuracy of ERUS in patients with rectal tumors who later underwent TEM, and to analyze the factors that influence this accuracy. Observational study including prospective data collection of patients with rectal tumors undergoing TEM with curative intent between June 2004 and May 2016. Preoperative staging by EUS (uT) was correlated with the pathology results after TEM (pT). The accuracy of the EUS was evaluated and a series of variables (tumor morphology, height, lesion size, quadrant, definitive pathology, the surgeon assessing the ERUS, and waiting time from the date of the ERUS until surgery) were analyzed as possible predictors of diagnostic accuracy. Six hundred and fifty-one patients underwent TEM, of whom 495 met the inclusion criteria. The overall accuracy of EUS was 78%, sensitivity 83.78%, specificity 20%, PPV 91.3%, and NPV 11%. Forty patients (8.08%) were understaged and 50 (10.9%) were overstaged. In the multivariate analysis, the surgeon's experience emerged as the most important predictor of accuracy (p < 0.001; OR 2.75, 95% CI 1.681-4.512). The EUS was less accurate with larger lesions (p = 0.004; OR 0.219, 95% CI 0.137-0.349) and when the definitive diagnosis was adenocarcinoma (p < 0.001; OR 0.84, 95% CI 0.746-0.946). ERUS accuracy rates are variable and there is a possibility of understaging and overstaging that must be taken into consideration. This accuracy is dependent on the operator's experience as well on lesion size; in addition, it is lower for lesions shown to be cancers in the final pathology report.
Keywords: Accuracy; Endorectal ultrasound; Rectal tumors; Transanal endoscopic surgery.