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Ultrasound scan of the back passage (rectum)

You might have this scan if you have cancer in your back passage (rectal cancer). It uses sound waves to look at the inside of your back passage (rectum).  It can show how big the cancer is, and whereabouts it is in the rectum.

It is also called a Trans Rectal Ultrasound (TRUS) or an Endorectal ultrasound (ERUS).

What is an ultrasound scan?

Ultrasound scans use high frequency sound waves to create a picture of a part of the body.

They can show up changes, including abnormal growths. You might have one to diagnose a cancer or find out if it has spread.

The ultrasound scanner has a microphone that gives off sound waves. The sound waves bounce off the organs inside your body and a microphone picks them up. The microphone links to a computer that turns the sound waves into a picture.

You usually have them in the hospital x-ray department.

A healthcare professional trained in ultrasound (sonographer) usually carries out the ultrasound in the hospital x-ray department.

Why you might have an ultrasound of your back passage?

You might have an ultrasound scan to find out where the cancer is in your rectum. It can also show the doctor how large your cancer is, how far it has grown through the rectal wall, and whether it has spread further. This helps your doctor decide about your treatment.

Preparing for your ultrasound

You need to make sure you  open your bowels beforehand, so your rectum is empty when you go for your appointment.

You might have a small enema, to help with this. An enema is a pouch filled with a small amount of liquid. You put the liquid into your back passage through a nozzle and it helps you empty your bowels.

What happens

The sonographer will ask you to remove your lower clothes and underwear. They will give you a gown to wear and possibly paper shorts, with an opening at the back.

You lie on the couch, on your left side.

The doctor gently pushes an ultrasound probe inside your back passage (rectum). The probe is about the same size as a finger. They use a cold lubricating gel to make this more comfortable. 

They will look at the pictures of the inside of you back passage on a computer screen. The scan should only take a few minutes. 

What happens afterwards

You can eat and drink normally after the test. You can go straight home or back to work afterwards.

Getting your results

You usually get your results within a few weeks of your test. Your specialist will give them to you. Your GP may also receive a copy of the results. 

Waiting for results can be an anxious time. It might be useful to talk to someone close to you.

If you want to talk to someone, you can contact our team of specialist cancer information nurses. Call free on 0808 800 4040, 9am to 5pm, Monday to Friday.

Possible risks

Ultrasound of the back passage (rectum) is a very safe procedure but your nurse will tell you who to contact if you have any problems after your test. Your doctors will make sure the benefits of having an ultrasound outweigh any possible risks.

Last reviewed: 
23 Aug 2018
  • Primary colon cancer: ESMO Clinical Practice Guidelines for diagnosis, adjuvant treatment and follow-up
    R Libianca and others
    Annals of Oncology, 2010. Volume 21, Pages 70-77

  • Rectal cancer: ESMO Clinical Practical Guidelines for diagnosis, treatment and follow up
    R Glynne-Jones and others
    Annals of Oncology, 2017. Volume 28, Pages 422-440

  • Association of Coloproctology of Great Britain & Ireland (ACPGBI): Guidelines for the management of cancer of the colon, rectum and anus (2017) – diagnosis, investigations and screening
    C Cunnigham and others
    Colorectal disease, 2017. Volume 19, Pages 1-97

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