Endorectal ultrasonographic staging of rectal carcinoma. Endorectal ultrasonography is a valuable imaging method for examination of the rectum and perirectal tissues. We assessed 50 patients with known rectal carcinoma prospectively by using a 7.0-MHz endorectal transducer to determine the depth of invasion of the rectal wall by tumor and the presence of lymphadenopathy. Tumors were staged by using the Astler-Coller modification of the Dukes staging system, and the results were compared with histologic staging of the surgical specimen. Ultrasonography had an accuracy of 80%, a sensitivity of 92%, and a specificity of 76% for detection of invasion of the perirectal fat. Ultrasonography was sensitive in the detection of perirectal lymphadenopathy but was not specific in distinguishing benign from malignant nodes. 