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Ultrasound of the anus

This scan uses sound waves to look at your anus.  It can show the size and position of your cancer.

It is also called an endoanal ultrasound or an endorectal ultrasound.

What is an ultrasound?

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.

Having an anal ultrasound is uncomfortable but shouldn't hurt. You usually have it 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 anus?

You might have an ultrasound scan to find out where the cancer is in your anus. It can also show the doctor how large your cancer is and how far it has grown. This helps your doctor decide about your treatment.

Preparing for your ultrasound

You might need to empty your bowels before an ultrasound to the anus. If this is the case your nurse will let you know before your appointment.

They might give you an enema to help you to do 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

A sonographer or your doctor carries out the ultrasound. They ask you to remove your lower clothes and underwear and 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.

They gently pushes an ultrasound probe inside your anus. 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 and can go straight home or back to work afterwards. 

Possible risks

Ultrasound scans are a very safe procedure. It doesn’t involve radiation and there are usually no side effects.

Getting your results

You should get your results within 1 or 2 weeks at a follow up appointment.

Waiting for test results can be a worrying time. You can contact your specialist nurse if you’re finding it hard to cope. It can also help to talk to a close friend or relative about how you feel.

For support and information, you can call the Cancer Research UK nurses on freephone 0808 800 4040. The lines are open from 9am to 5pm, Monday to Friday.

Contact the doctor that arranged the test if you haven't heard anything after a couple of weeks.

Last reviewed: 
09 Apr 2019
  • Anal cancer:ESMO-ESSO-ESTRO Clinical Practice Guidelines for diagnosis, treatment and follow-up
    R Glynne-Jones and others
    Annals of Oncology, 2015. Volume 25, Pages iii10-iii20

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