Transrectal ultrasonography for the assessment of invasion of rectal carcinoma.

To make objective and accurate assessment of depth of invasion in rectal carcinoma, transrectal ultrasonography was performed on 49 patients with rectal carcinoma. Two types of scanners were available for use; i.e., 5.0 MHz linear array scanner and 3.5 MHz radial scanner. An experimental study using fresh specimen revealed that the middle low echoic layer of the rectal wall corresponded to the muscularis propria. Depth of cancer invasion was assessed as to whether or not invasion had reached the muscularis propria, or whether invasion had gone through the muscularis propria. The result of 5.0 MHz linear array scan was superior to 3.5 MHz radial scan, and was fairly satisfactory. Future studies, using a sonographic probe with higher frequency and better resolution, are expected to produce valuable benefits in deciding indications for local excision of rectal carcinomas.