PURPOSE:Preoperative staging of advanced carcinoma of the rectum by conventional endorectal ultrasonography is often impossible because of the presence of obstruction, which does not allow passage of the endoprobe. In a prospective Study, we investigated the value of three‐dimensional endorectal ultrasonography for staging of obstructing rectal cancer. This technique permits examination of obstructing rectal tumors because scan planes can be chosen deliberately within a scanned volume.METHODS:Overall obstructing tumors not accessible for conventional endoprobes were found in 26 of 94 patients who were subjected to endorectal ultrasonography for staging of rectal cancer. Three‐dimensional volume scanning was performed using a three‐dimensional frontfire transducer or a three‐dimensional bifocal multiplane transducer (7.5/10 MHz). Data of the three‐dimensional scans were stored on a hard disk for subsequent evaluation with a combison 530 processor.RESULTS:Three‐dimensional transrectal endosonography enabled visualization of local tumor spread in all 26 patients. In 18 patients, obstruction was caused by advanced primary rectal carcinoma. Endosonography accurately determined the tumor infiltration depth in three T2 tumors, eight T3 tumors, and three T4 tumors. Overall accuracy for assessment of infiltration depth was 78 percent. Accuracy for assessment of perirectal lymph node involvement was 75 percent. In eight patients, the obstruction was attributable to extramural regrowth of rectal cancer after surgery. Diameter of the lesions ranged between 3 and 6 cm. Although all lesions were clearly depicted by three‐dimensional endosonography, only five lesions (62 percent) were detected by computed tomography.CONCLUSIONS:Three‐dimensional endorectal ultrasonography provides previously unattainable scan planes and enables accurate staging of obstructing rectal tumors. This technique may improve therapy planning in advanced rectal cancer by selecting patients who require preoperative adjuvant therapy.