Pitfalls and sources of error in staging rectal cancer with endorectal us.

Endorectal ultrasound (US) is an accurate technique for local staging of rectal cancer. Because the choice of surgery depends on the level of tumor invasion and lymph node involvement, the surgeon relies largely on endorectal US findings when planning treatment. However, staging inaccuracies can occur due to over or underestimation of tumor depth, misinterpretation of lymph node involvement, and operator inexperience. Technical pitfalls in US of the rectal wall include proximity of the lesion to the anal verge, improper balloon inflation, a nonperpendicular imaging plane, shadowing artifacts due to air or stool, reverberation artifacts, refraction artifacts, and a transducer gain setting that is too high. Sources of error in tumor staging with endorectal US include interpretation differences, endosonologist bias, tumor location, tumor stenosis, peritumoral inflammation, postbiopsy and postsurgical changes, post irradiation changes, hemorrhage, and pedunculated or villous tumors. Node size and appearance are not reliable indicators of lymph node involvement. Awareness of these sources of error will improve the technical quality of endorectal US studies and allow more accurate tumor staging.