[Contribution of endorectal ultrasonography in preoperative evaluation for very low rectal cancer]

Abdominoperineal resection is the standard treatment of very low rectal carcinoma. Pretherapeutic evaluation of locoregional extension relies mainly on digital rectal examination. The interest of endorectal ultrasonography to assess lateral and inferior margins is still to be determined.

To assess the ability of endorectal ultrasonography to evaluate the possibility of conservative anal sphincter surgery.

Between April 1996 and June 1998, 34 patients (20 men, 14 women, mean age: 61 years, range: 43-80) have been treated for rectal adenocarcinoma. Endorectal ultrasonography was made with a linear probe (EUP-U33). Before treatment, the mean distance between the lower pole of the tumor and the anal verge was 3.9 cm (range: 2-5), and between the lower pole and the puborectalis sling 2.3 mm (range: 0-7). A uTN classification was made. Preoperative treatment was radiotherapy (40 Gy in 4 patients, 60 Gy in 24 patients), or radiochemotherapy (6 patients). Pre- and post-radiotherapy endorectal ultrasonography results were compared to the patholocical analysis of operative specimen.

Wall infiltration was correctly evaluated in 57% of patients after radiotherapy. In 26/34 cases, a safe plane existed before and after radiotherapy, and correlation of endorectal ultrasonography with histology was 96%. For patients without safe plane, correlation with histology was 75%.

For very low rectal tumors, with an aggressive sphincter conservation approach, endorectal ultrasonography allows to assess sphincter invasion with 96% fiability when safe plane exists.