Endorectal ultrasound scan (ERUS)

This test might sometimes be done to help plan surgery for rectal cancer. 

Ultrasound scans use sound waves to build up a picture of body tissues. An endorectal ultrasound scan can show the size and position of cancer in the rectum.

For the test, you lie on your left side with your knees bent up. A nurse or doctor gently passes a small, lubricated probe into the back passage. This produces an image of the rectum on a screen.

The scan takes about 10 minutes. You can usually go home as soon as it is over.