Imaging diagnostics in proctology – ultrasound, resonance imaging, tomography

Content author: MD. Sara Godyńska, proctologist · Editorial work: Editorial team of Wyspa Medycyny Przyjaznej · Medical review: lek. Sara Godyńska · Date of creation: 07.08.2026 · Date of review: 07.08.2026 · Updated: 07.08.2026

The article is of an educational nature and does not replace a proctological examination or qualifications for imaging tests. Fever with severe pain around the anus, rapidly spreading redness, discharge of pus, urinary retention, heavy bleeding and sudden fecal incontinence require immediate medical attention - without waiting for an imaging examination.

The most important information at a glance

• Diagnostic imaging does not replace proctological examination - it supplements it with what cannot be seen and cannot be felt.
• The three main methods are endoanal ultrasound, pelvic magnetic resonance imaging and computed tomography.
• Endoanal ultrasound is fast, without radiation and very good at assessing sphincters and lesions close to the anal canal.
• Magnetic resonance imaging best shows the course of complex fistulas and their relationship to the sphincter muscles.
• Computed tomography is useful in emergency situations and in the assessment of complications in the abdominal cavity.
• The choice of method depends on the clinical problem, not on which method is "better".
• Imaging tests do not replace endoscopy or histopathological examination - they do not diagnose cancer.
• When a fistula is suspected, a precise assessment of the course of the canal has a direct impact on the choice of the surgical method.
• The assessment of sphincters is particularly important in women after childbirth and before planned surgery in this area.
• Magnetic resonance imaging has contraindications - all implanted devices and metal elements must be informed before the examination.

Find out more about the specialist

Doctor. Sara Godyńska is a proctologist at Wyspa Medycyny Przyjaznej in Gdańsk. He deals with the diagnosis and treatment of diseases of the anal area. Imaging tests are ordered in proctology when they answer a specific clinical question - for example, where the fistula runs or whether the sphincters are intact. A "just in case" test usually brings nothing except cost and expectation.

Meet the doctor. Sara Godyńska

What you can't see in the office

Proctological examination - examining the area, finger examination and anoscopy - allows you to assess the skin around the anus, the tension of the sphincters and the anal canal from the inside. This is a lot and in most cases it is enough to make a diagnosis.

However, there are situations in which the clinical picture says "there is something here" but does not say where or how deep. Classic examples are:

• anal fistula, the external opening of which is visible, but the course of the canal remains unknown,
• an abscess located deeper, beyond the reach of finger examination,
• damage to the sphincter muscles, invisible from the outside,
• a rectal tumor, in which the depth of wall invasion must be assessed,
• defecation disorders, where the problem concerns the mechanics and not the appearance of the area,
• recurrences after previous surgeries when the anatomy is altered by scarring.

In each of these situations, the imaging test answers a specific question - and that is the right way to think about diagnosis. An examination is not ordered "just to see", but to resolve a specific doubtthat will change the course of action.

Three methods in comparison

This comparison shows the most important conclusion: none of these methods is universally better. They answer various questions and complement each other in many situations - for example, in the case of a complex fistula, MRI shows the course of the canal, and endoanal ultrasound precisely assesses the condition of the sphincters before surgery.

Endoanal and transrectal ultrasound

This is an ultrasound examination performed with a special head inserted into the anal canal or rectum. The head emits high-frequency waves and allows for a magnified view of the structure of the anal canal wall - including both sphincter muscles.

What is it used for:

• assessment of the continuity and thickness of sphincter muscles - crucial for fecal and gas incontinence,
• detection of sphincter damage after childbirth, including those that did not cause symptoms immediately after delivery,
• localization of abscesses located close to the anal canal,
• assessment of fistulas straight course and their relationship to the sphincters,
• assessment of the depth of wall infiltration in rectal lesions,
• control after procedures in this area.

Advantages: no radiation, short time, feasibility in outpatient conditions, very good resolution in the immediate vicinity of the anal canal and can be repeated without restrictions.

Limitations: small range - the test will not assess structures located further from the warhead; a clear dependence of the result on the experience of the person performing it; limited usefulness in very painful lesions when insertion of the transducer is difficult.

It is worth expanding on the point about sphincters, because it concerns a situation that is often overlooked. Damage to the sphincters during childbirth may be asymptomatic for years, and problems with holding gases or stools appear only after some time. Endoanal ultrasound allows you to assess whether such damage has occurred - and this changes both the management and planning of possible procedures in this area.

Magnetic resonance imaging of the pelvis

MRI uses a strong magnetic field and radio waves. It does not use ionizing radiation, and its greatest advantage is the excellent differentiation of soft tissues - which is exactly what we deal with in the pelvis.

We write more about the study itself here: magnetic resonance imaging.

What is it used for in proctology:

• assessment of the course of anal fistulas, especially complex, multi-channel and recurrent ones,
• determining the relationship of the fistula canal to the sphincter muscles - information directly influencing the choice of surgical method,
• detection of abscesses and purulent stains located deep in the pelvis,
• assessment of local advancement of rectal tumors,
• diagnosis of changes in the course of inflammatory bowel diseases,
• assessment of the causes of chronic pain in the anal area when other tests do not provide an answer.

The first two points deserve to be emphasized because they explain why MRI has become a basic examination in the case of fistulas. An anal fistula is a channel that runs between the intestine and the skin - and its key feature is that how it runs in relation to the sphincters. This determines whether the procedure can be performed without risk to fecal continence or whether a sparing technique must be chosen. Operating a fistula without knowing its course is a procedure with a much higher risk of recurrence and complications.

Contraindications and limitations: All implanted devices and metal elements must be informed about before the examination - this applies to pacemakers, cochlear implants, vascular clips, neurostimulators and others. Some modern devices are conditionally approved, but the decision is made by the center performing the test. The examination also requires prolonged immobility in a narrow space, which can be difficult in cases of claustrophobia. When administering a contrast agent, renal function is additionally assessed.

Computed tomography

Computed tomography uses X-rays and allows you to obtain a cross-sectional image of the body in a very short time. In proctology, its application is narrower than MRI, but in certain situations it is the method of choice.

We write more about the study itself here: computed tomography.

What is it for:

• quick assessment in emergency situations - when extensive infection or complications requiring an urgent decision are suspected,
• detection of abscesses located higher, in the abdominal cavity and pelvis,
• assessment of complications of colorectal diseases,
• assessment of the spread of cancer, including examination of the chest and abdominal cavity,
• diagnostics in patients for whom MRI is contraindicated or impossible to perform.

Advantages: very short examination time, wide availability, good assessment of abdominal structures and the possibility of performing it in a patient in a serious condition.

Limitations: ionizing radiation, weaker differentiation of pelvic soft tissues than in MRI - therefore, in the case of fistulas and assessment of sphincters, tomography is inferior to other methods. When administering a contrast agent, it is necessary to assess kidney function and ask for allergic reactions.

The issue of radiation needs to be faced honestly. The dose in a single study is controlled and justified when the study is expected to change management. However, it is not neutral when repeated repeatedly - and this is one of the reasons why non-radiation methods are preferred in young patients who require long-term follow-up.

Which test for which problem

It is worth paying attention to the fifth line. In the case of rectal bleeding, imaging tests are usually not the first step - the source of the bleeding is determined by proctological examination, anoscopy, and, if indicated, endoscopy of the large intestine. MRI or tomography will not answer the question whether a hemorrhoid, fissure or polyp is bleeding.

What imaging cannot replace

This fragment is as important as the description of the capabilities of individual methods - because patients often expect answers from an imaging test that it does not provide.

• It will not replace a proctological examination. Many diagnoses are made in the office, and imaging only clarifies the details.
• It will not replace endoscopy. Assessment of the colon mucosa, collection of biopsies and removal of polyps require colonoscopy.
• Does not diagnose cancer. Imaging shows the lesion and its extent; the diagnosis is made by a pathologist based on microscopic examination.
• Does not evaluate the activity. In case of defecation disorders and fecal incontinence, functional tests are needed to assess the functioning of the sphincters, not only their structure.
• Does not replace an interview. The same image with different symptoms can be interpreted differently.

Hence the rule that organizes all diagnostics in this field: an imaging test is ordered when its result changes the procedure. If the treatment plan is the same regardless of the result, the test only means cost, waiting time and - in the case of CT scan - an unnecessary dose of radiation.

How to prepare for the examination

The rules vary between centers, so detailed recommendations are always provided by the laboratory performing the examination. Below is a general framework that is worth knowing in advance.

The last line is the most underestimated in practice. Previous imaging studies - even from years ago - allow you to compare the image over time and often change the interpretation. It's worth taking them with you, also on CD.

A referral with a specific clinical question is equally important. The description "I am asking for an MRI of the pelvis" gives less information than "suspicion of an anal fistula, assessment of the course of the canal and the relationship to the sphincters" - the radiologist then knows what to look for and how to select the examination sequence.

The most common myths

• "Resonance will detect everything." No. It does not assess the intestinal mucosa or provide a histopathological diagnosis.
• "Tomography is more accurate than MRI." No. In the assessment of pelvic soft tissues, MRI is better; CT scan wins in terms of speed and assessment of the abdominal cavity.
• "When bleeding, imaging first." No. The source of the bleeding is determined by proctological examination and endoscopy.
• "Endoanal ultrasound is the same as regular abdominal ultrasound." No. This is an examination with a special head that assesses the structure of the anal canal and sphincters.
• "If the imaging is normal, I'm fine." Not always. Some problems are functional in nature and are not visible in structural tests.
• "The fistula can be operated on without imaging." It may be possible in the case of a simple course, but in the case of complex and recurrent pathologies, the assessment of the course of the canal is crucial.
• "Resonance is an examination for everyone." No. It has contraindications that must be informed before the examination.
• "The more research, the better." No. The study makes sense when its results change the course of action.

Do you have a referral for a test or don't know if it is needed?

The clinical question, not the diagnosis itself, determines the selection of the test. A proctological consultation allows you to determine whether imaging is necessary in your case and which one will be appropriate.

Proctology and imaging diagnostics at the Island of Friendly Medicine in Gdańsk

At the Island of Friendly Medicine, doctor. Sara Godyńska consults patients with diseases of the anal area. The visit includes an interview, proctological examination and determining whether diagnostic imaging is needed - and if so, which test will answer the clinical question.

We have imaging diagnostics, including magnetic resonance imaging and computed tomography. The current scope of tests, availability of dates, prices and preparation rules should be confirmed during registration.

Find out more about the medicine. Sara Godyńska Magnetic resonance imaging Computed tomography

What to ask the doctor?

• What question is this study supposed to answer?
• Will the result change the treatment method?
• Why this study and not others?
• Will I need a contrast agent?
• How should I prepare?
• Are my implants or devices a contraindication to MRI?
• Should I report kidney or thyroid disease?
• How long does the examination take and will it be unpleasant?
• When will I know the result and who will discuss it with me?
• Is endoscopy also needed?
• Is it worth taking previous tests?
• What next if the result is normal but the symptoms remain?

FAQ - imaging diagnostics in proctology

Why are imaging tests performed in proctology?

To assess what cannot be seen in the office: the course of the fistula, the depth of the abscess, the continuity of the sphincters or the extent of the lesion in the rectal wall. The test is ordered when its result changes the procedure.

Which test is best?

Neither is universally best. Endoanal ultrasound is best for assessing sphincters, MRI, the course of complex fistulas and soft tissues of the pelvis, while tomography is useful in emergency situations and when assessing the abdominal cavity.

What is endoanal ultrasound?

During an ultrasound examination performed with a special transducer inserted into the anal canal. It allows for a magnified assessment of the structure of the canal wall, including both sphincter muscles. Does not use radiation.

Does endoanal ultrasound hurt?

It is usually felt but not painful - it resembles a proctological examination and lasts only a short time. In very painful lesions, insertion of the transducer may be difficult and another examination is considered.

Why is an MRI ordered in the case of a fistula?

Because it is crucial where the fistula tract runs and how it passes through the sphincters. The choice of surgical technique and the risks to fecal continence depend on this. In the case of complex and recurrent fistulas, this information is necessary.

What are the contraindications to MRI?

All implanted devices and metal elements - pacemakers, implants, clips, neurostimulators - must be informed before the examination. Some of them are conditionally admitted, and the decision is made by the center performing the test.

Is tomography harmful?

Uses ionizing radiation, and the dose in a single examination is controlled and justified when the examination changes the management. When multiple inspections are necessary, non-radiation methods are preferred.

Will imaging detect colon cancer?

It can show the change and its extent, but it does not provide recognition. Assessment of the mucosa and collection of biopsies require colonoscopy, and the diagnosis is made by histopathological examination.

Do I need imaging for rectal bleeding?

Usually not in the first place. The source of the bleeding is determined by proctological examination, anoscopy and, if indicated, endoscopy of the large intestine. Imaging tests do not answer the question of what is bleeding.

When are sphincters assessed?

In case of fecal and gas incontinence, after childbirth complicated by perineal damage and before planned procedures in the anal area, when there is a risk to the sphincter apparatus.

How to prepare for the test?

Policies vary between laboratories and they provide detailed recommendations. It is always worth taking a referral, previous results and descriptions, and a list of medications taken.

Who qualifies for testing at WMP?

On the WMP website, MD. Sara Godyńska is described as a proctologist dealing with the diagnosis and treatment of diseases of the anal area. The scope of available tests and dates are confirmed by registration.

Sources

• Island of Friendly Medicine, MD. Sara Godyńska: https://www.wyspamedycynyPrzyjaznej.pl/pl/sara-godynska-proktolog
• Wyspa Medycyny Przyjaznej, proctological consultation: https://www.wyspamedycynyPrzyjaznej.pl/pl/konsultacja-proktologiczna-gdansk
• Wyspa Medycyny Przyjaznej, magnetic resonance imaging: https://www.wyspamedycynyPrzyjaznej.pl/pl/rezonans-magnetyczny
• Island of Friendly Medicine, computed tomography: https://www.wyspamedycynyPrzyjaznej.pl/pl/tomografia-komputerow
• NHS, MRI scan: https://www.nhs.uk/conditions/mri-scan/
• NHS, CT scan: https://www.nhs.uk/conditions/ct-scan/
• NHS, Ultrasound scan: https://www.nhs.uk/conditions/ultrasound-scan/
• NHS, Anal fistula: https://www.nhs.uk/conditions/anal-fistula/
• NHS, Anal abscess: https://www.nhs.uk/conditions/anal-abscess/
• NHS, Bowel incontinence: https://www.nhs.uk/conditions/bowel-incontinence/
• NHS, Bowel cancer: https://www.nhs.uk/conditions/bowel-cancer/
• NICE, Colorectal cancer (NG151): https://www.nice.org.uk/guidance/ng151
• NICE, Suspected cancer: recognition and referral (NG12): https://www.nice.org.uk/guidance/ng12
• American Society of Colon and Rectal Surgeons, Clinical Practice Guidelines: https://fascrs.org/healthcare-providers/education/clinical-practice-guidelines