Preoperative staging of patients with rectal tumors suitable for transanal endoscopic microsurgery (TEM): comparison of endorectal ultrasound and histopathologic findings.

Background: Accurate preoperative staging is the key to correct selection of rectal tumors for local excision. This study aims to assess the accuracy of endorectal ultrasound (ERUS) at our institution.

Methods: Retrospective analysis was carried out of patients treated by transanal endoscopic microsurgery (TEM) from 1996 to 2008. TEM was considered the treatment of choice for uT0-1/N0 lesions located between 2 and 12 cm from the anal verge. It was also proposed in selected uT2-3 patients. Preoperative staging was compared with histopathologic findings.

Results: Eighty-one patients (46 males, mean age 66 years) underwent TEM. Mean distance of the tumor from the anal verge was 6.6 cm (range 2-12 cm). ERUS staged 15 of 27 adenomas (55%) as uT1. Of 54 carcinomas, 5 were pT0 because TEM was performed to remove resection margins of a malign polyp already snared. Five of 19 pTis (26%) were overstaged uT1, while 7 of 17 pT1 (41%) were understaged. Overall, ERUS enabled distinction between early and advanced rectal lesion with 96% sensitivity and 85% specificity, giving accuracy of 94% (65/67). Thirteen patients had advanced lesions (eight pT2 and five pT3). Only in two of them (15%) was depth of invasion underestimated by ERUS (one uT0, one uT1) and thus was subsequent salvage surgery necessary.

Conclusions: ERUS is useful to confirm the diagnosis of adenoma and predict depth of mural invasion in early rectal cancer. Differentiation between T0/is and T1 lesions remains challenging, however this does not usually influence surgical strategy.