Diagnostic accuracy of 1,000 endorectal ultrasounds before transanal endoscopic microsurgery for rectal neoplastic lesions

Introduction Endorectal ultrasound (EUS) is an essential tool for local staging of rectal neoplasia; however, its diagnostic accuracy in distinguishing non-invasive from invasive lesions before transanal endoscopic microsurgery (TEM) remains a matter of debate. Methods A retrospective analysis of 1,000 consecutive EUS examinations performed before TEM between 1993 and 2025 was conducted using a prospectively maintained database. EUS levels (0–3) were correlated with the final histopathological outcome. Lesions were categorised as non-invasive (LGD, HGD, Tis) or invasive (pT1–pT3). Diagnostic metrics—sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and accuracy—were calculated overall and across three chronological periods. Separate analyses were performed for post-neoadjuvant (ypT03) and post-endoscopic resection groups. Results Among 883 evaluable EUS studies for the primary analysis (non-invasive vs invasive pT1–pT3), overall sensitivity was 86.4%, specificity 64.9%, PPV 81.5%, NPV 72.7%, and accuracy 78.7%. All indices improved over time, with accuracy rising from 62.9% in early cases to 73.9% in the most recent period. In the post-neoadjuvant group ( n = 47), sensitivity remained high (89.7%), but specificity was low (33.3%), likely due to overstaging related to fibrosis. In the post-endoscopic resection group ( n = 70), the apparent accuracy was 44.3%, suggesting a high rate of false-positive invasion predictions. Conclusions EUS before TEM shows good overall accuracy and excellent reliability for excluding deep invasion, with progressive improvement over the past 3 decades. While overstaging remains a limitation in post-treatment and non-dysplastic lesions, EUS continues to play a pivotal role in selecting candidates for organ-preserving rectal surgery. In post-endoscopic resection scars and post-neoadjuvant rectum, EUS findings should be interpreted cautiously and integrated with MRI/endoscopic morphology.