Diverticulosis is most often discovered incidentally, meaning it shows up on imaging or during a colonoscopy done for an unrelated reason. Because diverticulosis rarely causes symptoms on its own, there’s no single screening test specifically designed to find it. Instead, the diagnosis typically comes as a secondary finding during routine colorectal cancer screening or when imaging is ordered for abdominal complaints. About 60% of Americans have diverticulosis by age 60, and most never know it until a test reveals the small pouches (diverticula) lining their colon wall.
Colonoscopy: The Most Common Way It’s Found
The majority of diverticulosis diagnoses happen during a routine colonoscopy. In one prospective study of 823 patients undergoing standard colorectal cancer screening, 27.2% were found to have incidental diverticulosis. That’s roughly one in four people walking in for a cancer screening who walk out with a diverticulosis finding on their report.
During a colonoscopy, a gastroenterologist threads a flexible camera through your colon. Diverticula are easy to spot visually: they appear as small openings or pockets in the colon wall, most commonly in the sigmoid colon (the lower left portion). The doctor can note how many there are, where they’re located, and whether the surrounding tissue looks inflamed. If the tissue looks normal and there’s no sign of bleeding or inflammation, the finding is simply documented as diverticulosis, and no further workup is typically needed.
Preparation for a colonoscopy involves a clear liquid diet starting the day before and a bowel-cleansing laxative regimen. The procedure itself is done under sedation and usually takes 30 to 60 minutes. You won’t feel pain during the exam, though some bloating and grogginess afterward are normal.
CT Scans: The Go-To for Symptoms
If you show up with abdominal pain, particularly in the lower left side, a CT scan of the abdomen and pelvis is the primary tool used to figure out what’s going on. CT imaging is highly accurate for evaluating the colon, with a sensitivity and specificity of about 95% to 96% for diverticular disease. It can show the diverticula themselves and, critically, whether any of them are inflamed or causing complications.
This distinction matters because clinical suspicion alone, meaning a doctor’s assessment based on your symptoms and physical exam, is only correct 40% to 65% of the time when diverticulitis is suspected. That’s why the American Gastroenterological Association recommends CT imaging to confirm the diagnosis in anyone without a prior imaging-confirmed case. The scan is especially important for people with severe symptoms, those who aren’t improving with treatment, or anyone with a weakened immune system.
A CT scan for diverticular disease typically uses both oral and intravenous contrast (a dye that helps highlight structures on the images). You’ll likely be asked to fast for a few hours beforehand and drink a contrast solution. The scan itself takes only a few minutes, and you can usually go home the same day.
How Imaging Tells Diverticulosis From Diverticulitis
One of the key reasons imaging matters is that diverticulosis and diverticulitis look very different on a scan. Diverticulosis alone shows small outpouchings along the colon wall with no surrounding changes. Diverticulitis, on the other hand, shows those same pouches plus visible inflammation: thickening of the bowel wall, streaky changes in the surrounding fat (called fat stranding), and sometimes fluid collecting near the colon.
Radiologists look for specific patterns. In diverticulitis, the fat stranding around the colon tends to be “disproportionate,” meaning it’s more severe than you’d expect given the degree of bowel wall thickening. An inflamed diverticulum appears as a rounded outpouching surrounded by inflammation. In more complicated cases, the scan can reveal abscesses, perforations, or narrowing of the colon. These distinctions help determine whether you need antibiotics, hospital admission, or potentially surgery.
Ultrasound as an Alternative
Abdominal ultrasound can also detect diverticular disease, and it has the advantage of being completely radiation-free and available at the bedside. It’s used more frequently in Europe than in the United States. A meta-analysis of 12 studies covering over 2,000 patients found that ultrasound has a sensitivity of 92.5% and specificity of 87.7% for detecting acute diverticulitis. Point-of-care ultrasound performed by the treating physician showed even better numbers: 94.1% sensitivity and 89.8% specificity.
The tradeoff is that ultrasound is more operator-dependent, meaning accuracy varies based on the skill of the person performing it. It also performs less well in patients with a higher body mass index, since excess abdominal tissue can obscure the view. For complicated diverticulitis involving abscesses or perforations, ultrasound’s sensitivity drops to about 58%, making CT the better choice when complications are suspected.
Other Imaging Options
MRI is very sensitive for detecting diverticular disease but less specific than CT, meaning it can sometimes flag inflammation that turns out to be something else. It’s generally not used in the acute setting and is more commonly reserved for patients who can’t receive CT contrast or who need to avoid radiation exposure, such as pregnant individuals.
Plain X-rays (standard abdominal films) cannot diagnose diverticulosis or diverticulitis on their own. They’re useful only for checking for complications like a free perforation, which shows up as air outside the bowel, or a bowel obstruction. If you go to an emergency room with severe abdominal pain, an X-ray might be the first test ordered, but it will almost always be followed by a CT scan if diverticular disease is suspected.
What Happens After Diagnosis
If diverticulosis is found incidentally during a colonoscopy and you have no symptoms, there’s usually nothing further to do. The finding is noted in your medical record, and your doctor may discuss dietary and lifestyle factors that could reduce the risk of developing diverticulitis down the line, such as eating more fiber and staying physically active.
If the diagnosis comes from a CT scan during an episode of suspected diverticulitis, the imaging findings guide the next steps. Uncomplicated cases with mild inflammation often resolve with dietary changes and sometimes antibiotics. Complicated cases involving abscesses or perforations may require drainage procedures or surgery. For patients whose first episode is confirmed by CT, a follow-up colonoscopy is often recommended 6 to 8 weeks after symptoms resolve. This is done to rule out an underlying colorectal cancer, which can occasionally mimic or coexist with diverticular disease on initial imaging.