Introduction

Tenesmus is an uncomfortable and frustrating symptom where a person feels a constant urge to pass stool, even when their bowels are already empty. This feeling often results from inflammatory bowel disease (IBD) like Crohn's disease or ulcerative colitis, but can also be caused by infections, motility disorders, tumours or haemorrhoids.¹

Imaging methods

To find the cause of tenesmus, doctors first need to identify its cause, whether it is inflammation, infection, or a tumour. Imaging tools like endoscopic imaging, X-ray imaging, computed tomography (CT) scans, magnetic resonance imaging (MRI), ultrasound imaging, and positron emission tomography-CT (PET-CT) scans may help pinpoint the problem and guide the right approach.^2,3

Endoscopic imaging

One of the most prevalent and convenient imaging techniques is endoscopic imaging. It involves inserting a small camera through the rectum to look directly at the inside of the bowel. It helps doctors spot inflammation, infections, or other signs of disease.⁴

X-ray imaging

X-rays are used to diagnose the underlying causes of tenesmus through a procedure called defecography, which involves taking real-time X-ray images of the rectum and pelvic floor during a bowel movement. A barium-based contrast material is inserted into the rectum to make the structures visible, allowing doctors to identify structural abnormalities, pelvic floor dysfunction, or other issues.⁵

Computed tomography (CT) scans

CT scans are a highly accurate tool used to detect deep problems in the body that other types of imaging might miss. They are helpful in the detection of tumours, inflammation, or abscesses in the lower abdomen and rectum. CT scans are noninvasive, making them a more practical and comfortable option than other procedures.⁶

Magnetic resonance imaging (MRI)

MRI shows soft tissues clearly and is often used to look for tumours or problems in the pelvic area. A special type called MRI defecography helps assess bowel movement issues.⁷

Ultrasound imaging

Transrectal ultrasound is one of the most convenient tools that provides high-resolution images of the rectal wall and nearby areas. It specialises in spotting abscesses or muscle problems.⁶

Positron emission tomography-CT (PET-CT) scans

PET-CT combines positron emission tomography (PET) and CT to provide detailed, functional images of the body, detecting metabolic and structural changes to diagnose and monitor various diseases. PET-CT provides detailed and precise images that help distinguish between different types of abnormal masses.⁸

Causes of tenesmus

The imaging tools mentioned above help doctors understand what is causing tenesmus by providing a clearer view of what is happening inside the body. These images guide treatment by revealing signs of conditions like inflammation, infection, or tumour. Common findings include:^1-3

• Inflammation (e.g., ulcerative colitis): swelling and irritation of the bowel lining
• Infection (e.g., colitis, proctitis): caused by bacteria or other harmful germs
• Tumour (e.g., rectal tumours): abnormal growths that may block or irritate the bowel
• Functional disorders (e.g., poor muscle control): problems with how the bowel moves or responds
• Structural issues (e.g., prolapse, fistula): physical damage or abnormal shape in the bowel

Clinical decision-making

Insights from imaging tools play a key role in helping doctors decide the appropriate treatment. The information they provide is essential for creating effective, personalised treatment plans. These plans may include medication, lifestyle changes, or a combination of therapies, all aimed at reducing symptoms and improving the patient’s quality of life.

FAQs

What is the most commonly used imaging technique for diagnosing what is causing tenesmus?

The most commonly used method is endoscopic imaging, which lets doctors see the inside lining of the rectum and colon. CT scans are used for detailed views of the abdomen and pelvis, and MRI defecography helps assess how the rectum and pelvic floor muscles are working. The choice of test depends on what the doctor suspects is causing the problem.

How does CT differ from MRI?

CT scans provide rapid, detailed imaging of the abdomen and pelvis, making them useful for detecting tumours, abscesses, or inflammatory conditions. MRI scans, especially pelvic MRI and MRI defecography, give clearer images of soft tissues. This makes them especially useful for spotting problems like rectal cancer, pelvic floor issues, and other conditions affecting the rectum.

When is a PET-CT scan recommended?

A PET-CT scan is usually done when doctors suspect colorectal or rectal cancer, or when they need to see if the tumour has spread. It works by measuring how active certain cells are, since cancer cells use more energy, which helps tell the difference between harmless and harmful growths.

How do imaging studies help differentiate between inflammatory and neoplastic causes of tenesmus?

Imaging tests like CT and MRI help doctors tell the difference between inflammation, such as in Crohn’s disease or ulcerative colitis, and more serious issues like colorectal cancer. Inflammatory conditions often show signs like swelling or irritation of the bowel wall, while cancer usually appears as an irregular lump, a narrowed section of the bowel, or nearby swollen lymph nodes.

What role does MRI defecography play in diagnosing functional causes of tenesmus?

MRI defecography helps doctors see how the rectum and pelvic floor muscles function during a bowel movement. It is especially useful for identifying functional problems, such as poor muscle coordination, rectal prolapse, or rectocele, that can lead to tenesmus. This scan provides real-time images, making it easier to understand why someone might feel a constant urge to pass stool.

Summary

Tenesmus, or the persistent and urgent need to pass stool or urine despite an empty rectum or bladder, is a symptom of a complex underlying condition, and accurate diagnosis is essential to determine the root cause and provide effective treatment. Imaging techniques and screening help identify the underlying cause, guiding timely and appropriate care. Health professionals, such as radiologists, physicians, and gastroenterologists, use this information to create treatment plans that improve patient comfort by reducing symptoms and supporting long-term health.