Bowel wall thickening seen by chance on a CT scan

What the report means

The report means part of the colon wall looked thicker than expected. A 2018 review says the normal colon wall should be no more than 3 mm thick when the bowel is filled out. Thickening can come from inflammation, polyps or cancer, but also from benign narrowing or a collapsed piece of bowel. (Chandrapalan 2018)

Words a CT report may use (simplified)
Report wording	What it describes
Colonic wall thickening, mural thickening, bowel wall thickening	The colon wall looks thicker than about 3 mm where the bowel is filled out (Chandrapalan 2018)(Karacin 2020)
Focal, segmental or diffuse	A short spot, a longer stretch, or a large part of the colon (Karacin 2020)
Symmetric or asymmetric	Even all the way round, or thicker on one side (Karacin 2020)
Collapsed or underdistended segment	A part of the bowel that was empty on the scan, which can look thick when it is not (Chandrapalan 2018)(Stermer 2008)

Why an empty bowel can look thick

A 2008 study says colon wall thickening may be wrongly reported as abnormal on CT when the bowel is collapsed or only partly filled. (Stermer 2008) The 2018 review says thickening should be judged only where the bowel is filled out, to avoid false alarms, and that the caecum, the start of the colon, moves more and collapses more easily, so it more often looks thick when it is not. (Chandrapalan 2018)

What studies found at colonoscopy

Review of 9 studies, 1,252 people. About 73% of people with thickening on CT had something abnormal at colonoscopy. When the CT suggested inflammation, it was confirmed in 97%. When the CT report suspected cancer, cancer was confirmed in about 63%. Cancer rates in the studies ranged from 14% to 27%, and many cancers were in people with no bowel symptoms. (Chandrapalan 2018)
Thickening as the only finding. In a 2008 study of 46 people whose CT showed only wall thickening, 65% had a normal colonoscopy and 9% had a neoplastic growth, which the study reports as benign. (Stermer 2008)
Thickening found by chance. In a 2020 study of 122 adults (average age 60), 52% had an abnormal colonoscopy, 19.6% had a neoplastic growth such as an adenoma polyp or cancer, and 6.5% had colon cancer. Thickening that was moderate to severe, short (focal) or uneven (asymmetric) was more often linked to a growth. (Karacin 2020)

These are results from groups in hospital studies, not a forecast for one person. The 2018 review notes the studies were small and often did not describe the thickening. (Chandrapalan 2018)

What comes next

No set guideline. The 2018 review and the 2020 study both say there are no definitive guidelines on when a colonoscopy is needed for this finding. (Chandrapalan 2018)(Karacin 2020) NICE NG12 bases colorectal referral on symptoms and a FIT stool test, not on CT wall thickening. (NICE NG12)
Colonoscopy. The 2018 review says a colonoscopy to confirm the finding is reasonable. (Chandrapalan 2018) The 2008 study says that many people with this finding need a colonoscopy anyway, for example those with a family history of colorectal cancer, a positive stool blood test, or age over 50. (Stermer 2008) See what to expect at a colonoscopy.
If polyps are found. The timing of the next colonoscopy then follows the polyp results. See colonoscopy after polyps.
If pouches are found. See diverticulosis found by chance.

Your doctor decides which follow-up fits your scan, your symptoms and your history.

Who it applies to

Adults told that a CT of the belly or pelvis done for another reason shows thickening of the colon wall. If you have bowel symptoms, the NHS advice below applies whatever the scan showed.

NHS, symptoms of bowel cancer: (NHS)

See a GP if you have any symptoms of bowel cancer, such as changes in your poo, blood in your poo, bleeding from your bottom, tummy pain, a lump in your tummy, bloating, or losing weight without trying.

Ask for an urgent GP appointment or get help from NHS 111 if:

your poo is black or dark red
you have bloody diarrhoea

Call 999 or go to A&E if:

you're bleeding non-stop from your bottom
there's a lot of blood or you see large blood clots when you poo

Routine age-based screening

A CT of the belly is not a colon screening test. Your routine colorectal screening stays on its usual schedule unless your doctor says otherwise. USPSTF recommends screening adults aged 45 to 75. (USPSTF) ACS advises adults at average risk to start at 45. (ACS) The NHS sends a home FIT kit every 2 years to people aged 50 to 74. (NHS screening) See colorectal cancer screening, the screening tests compared, CT colonography and stool test results.

Where they differ:

Colonoscopy for every case. The 2018 review calls a colonoscopy reasonable whenever thickening is seen on CT. (Chandrapalan 2018) The 2008 study says thickening as a single incidental finding should not by itself prompt a colonoscopy. (Stermer 2008) The 2020 study points to moderate to severe, focal or asymmetric thickening as the cases that need one. (Karacin 2020)
How often something is found. Abnormal colonoscopy rates were about 73% in the 2018 review, 52% in the 2020 study and 35% in the 2008 study when thickening was the only finding. (Chandrapalan 2018)(Karacin 2020)(Stermer 2008)
Screening start age. USPSTF and ACS start colorectal screening at 45. (USPSTF)(ACS) The NHS programme starts at 50. (NHS screening)

Your doctor decides what your result means for you.

Questions people ask

What does bowel wall thickening on a CT mean?

It means the wall of the colon (large bowel) looked thicker than expected in one or more places. A 2018 review says the normal colon wall should be no more than 3 mm thick when the bowel is filled out, and that thickening can come from inflammation, polyps, cancer, benign narrowing, or simply a collapsed piece of bowel. (Chandrapalan 2018)

Can the bowel just look thick on the scan?

Yes. Studies say a collapsed or partly filled colon can be reported as thick when it is not, and that the caecum (the start of the colon) collapses more easily. That is why reports and reviews say thickening should be judged where the bowel is filled out. (Chandrapalan 2018) (Stermer 2008)

Will I need a colonoscopy?

Often, but there is no set guideline. A 2018 review found that about 73% of people with wall thickening on CT had something abnormal at colonoscopy and called a colonoscopy reasonable. A smaller 2008 study found that when thickening was the only finding, 65% had a normal colonoscopy. Your doctor decides. (Chandrapalan 2018) (Stermer 2008)

How often is it cancer?

In studies it varies. Cancer was found in 14% to 27% of people in the studies the 2018 review looked at. In a 2020 study of 122 people with thickening found by chance, 6.5% had colon cancer and 19.6% had a neoplastic growth such as an adenoma polyp or cancer. (Chandrapalan 2018) (Karacin 2020)

Does this change my routine colon screening?

Your routine colorectal screening stays on its usual schedule unless your doctor says otherwise. USPSTF and ACS advise screening for average-risk adults from age 45, and the NHS offers a home test every 2 years from 50 to 74. (USPSTF) (ACS) (NHS screening)