Anal fissure after pelvic radiotherapy

An anal fissure is a split in the skin of the anus. This can be a side effect of pelvic radiotherapy.

What is an anal fissure?

After pelvic radiotherapy, the skin of the anus may become narrower and less stretchy. Sometimes a split develops in the skin of the anus. This is called an anal fissure. It can cause a sharp, intense pain when you pass a stool (poo).

Anal fissure treatment

Your doctor can usually prescribe creams to apply to the area that help it heal. It is important to avoid getting constipated, because this can make a fissure worse. Your doctor may prescribe a laxative to make it easier for you to go to the toilet.

If the fissure does not get better, your doctor may advise treating it with injections of botulinum toxin A (Botox®). These are given into the tissue that lines the anus. Botox® causes the muscle to relax, reducing the pain and increasing the blood flow which helps the fissure to heal.

Some people may need a minor operation to make a small cut in the muscle around the anus. This releases the tension in the muscle and allows the fissure to heal. You usually have this operation under a general anaesthetic, as a day patient.

About our information

  • References

    Below is a sample of the sources used in our pelvic radiotherapy information. If you would like more information about the sources we use, please contact us at

    Andreyev HJN, Muls AC, Norton C, et al. Guidance: The practical management of the gastrointestinal symptoms of pelvic radiation disease. Frontline Gastroenterology, 2015; 6, 53-72.

    Dilalla V, Chaput G, Williams T and Sultanem K. Radiotherapy side effects: integrating a survivorship clinical lens to better serve patients. Current Oncology, 2020; 27, 2, 107-112.

    The Royal College of Radiologists. Radiotherapy dose fractionation. Third edition. 2019. Available from: [accessed March 2021]. 

  • Reviewers

    This information has been written, revised and edited by Macmillan Cancer Support’s Cancer Information Development team. It has been reviewed by expert medical and health professionals and people living with cancer. It has been approved by Chief Medical Editor, Professor Tim Iveson, Consultant Medical Oncologist.

    Our cancer information has been awarded the PIF TICK. Created by the Patient Information Forum, this quality mark shows we meet PIF’s 10 criteria for trustworthy health information.