by Jason Wasserman MD PhD FRCPC
March 30, 2026
Diverticular disease is a common condition in which small pouches called diverticula form in the wall of the colon. It is one of the most frequently diagnosed conditions of the large intestine in adults over fifty, and most people who have it never develop serious problems. The term covers a spectrum of conditions:
- Diverticulosis. Diverticula are present in the colon but are not inflamed or infected. Most people with diverticulosis have no symptoms and only learn about it during a colonoscopy or imaging test performed for another reason.
- Diverticulitis. One or more diverticula become inflamed or infected, causing pain and other symptoms. This is the complication that most often brings people to medical attention.
Most patients with diverticular disease are diagnosed through imaging or colonoscopy, not through a tissue biopsy. A pathology report is generated when tissue is removed — either during a surgical procedure to treat complicated or recurrent diverticulitis, or when biopsies are taken during a colonoscopy to rule out other conditions such as inflammatory bowel disease or cancer. If you have a pathology report for diverticular disease, this article explains what the pathologist found in the tissue and what it means for your care.
What parts of the colon are affected?
Diverticula can form anywhere in the colon, but they develop most often in the sigmoid colon — the S-shaped section at the lower left end of the colon, just above the rectum. They may also appear in the descending colon on the left side of the abdomen. Less commonly, diverticula form in the transverse or ascending colon on the right side.
The sigmoid colon is particularly prone to diverticula because of its narrow diameter and the high pressure generated as stool is compressed and moved through this section. Diverticula develop when the inner lining of the colon is pushed outward through weak spots in the muscular wall, forming small pockets that protrude outward.
What causes diverticular disease?
The exact cause is not completely understood, but several contributing factors have been identified:
- Low-fiber diet. A diet low in fibre leads to harder, smaller stools that are more difficult to move through the colon. This increases the pressure inside the colon, which, over time, may cause the inner lining to push through weak points in the wall.
- Ageing. The risk increases with age as the colon wall gradually weakens. Diverticular disease is uncommon before the age of 40 and becomes increasingly common with each decade thereafter.
- Chronic straining during bowel movements. Repeated straining — often associated with constipation — places extra mechanical pressure on the colon wall and contributes to the formation of diverticula over time.
- Physical inactivity and obesity. These factors are also associated with a higher risk of developing diverticular disease and its complications, though the precise mechanisms are still being studied.
What are the symptoms?
Most people with diverticulosis have no symptoms at all. The pouches are often discovered incidentally during a colonoscopy or a CT scan performed for another reason.
When diverticulosis causes symptoms, they are usually mild and may include cramping or lower left abdominal discomfort, bloating, and changes in bowel habits such as constipation or alternating loose stools. These symptoms can be difficult to distinguish from irritable bowel syndrome.
Diverticulitis produces more noticeable symptoms because the inflammation and infection cause active injury to the colon wall. These typically include:
- Sudden, persistent pain in the lower left abdomen — this is the most characteristic symptom.
- Fever and chills.
- Nausea or vomiting.
- Diarrhea or constipation.
- Loss of appetite.
Rectal bleeding, while uncommon in diverticulitis, can occur with diverticular disease and should always be investigated by a doctor.
How is the diagnosis made?
Diverticular disease is most often diagnosed through a combination of the following:
- Medical history and physical examination. Your doctor will ask about your symptoms and check your abdomen for tenderness, particularly in the lower left quadrant.
- CT scan. A CT scan of the abdomen and pelvis is the most reliable way to confirm diverticulitis and look for complications such as an abscess or perforation.
- Colonoscopy. A flexible camera is used to look directly into the colon. Colonoscopy can identify diverticula and rule out other causes of symptoms — including polyps, inflammatory bowel disease, and cancer. It is usually performed several weeks after a diverticulitis episode has resolved, once any active inflammation has settled.
- Blood tests. An elevated white blood cell count can support a diagnosis of infection or inflammation.
A tissue biopsy is not usually taken during the acute phase of diverticulitis. If biopsies are taken, it is generally to rule out other conditions — the diagnosis of diverticular disease itself is usually established by imaging and colonoscopy rather than by pathology.
What does the pathology report describe?
When tissue is examined under a microscope — either from a surgical resection or from biopsies taken at colonoscopy — the pathologist may describe some or all of the following features.
Diverticula
Diverticula appear as small outpouchings or sacs that push through the muscular wall of the colon. In a surgical specimen, the pathologist can see these pouches directly and assess whether they show signs of inflammation. In biopsy specimens taken at colonoscopy, the pathologist may see the opening of a diverticulum or changes in the surrounding tissue.
Diverticulitis
When a diverticulum is inflamed, the pathologist sees immune cells — particularly neutrophils and lymphocytes — clustering around and within the diverticulum and the surrounding tissue. There may be areas of tissue damage and small pockets of infection called microabscesses.
Pericolonic abscess
An abscess is a localised pocket of pus and inflammatory cells. In diverticulitis, an abscess can form in the fat immediately surrounding the colon — this is called a pericolonic abscess. It develops when inflammation from a diverticulum spreads outward through the colon wall into the surrounding tissue. Pericolonic abscesses are a sign of more advanced diverticulitis and may require drainage or surgery in addition to antibiotics.
Perforation
A perforation is a tear or hole that develops in the wall of a diverticulum when inflammation has damaged it severely enough to cause it to rupture. If intestinal contents leak through the perforation into the abdominal cavity, it can cause a serious and potentially life-threatening infection called peritonitis. Perforation is a medical emergency that typically requires urgent surgery.
What happens next?
The next steps depend on the severity of the diverticular disease and whether any complications are present.
Diverticulosis (no inflammation)
Diverticulosis does not require specific medical treatment. The main focus is on reducing the risk of future diverticulitis. Increasing dietary fibre intake, staying well hydrated, exercising regularly, and maintaining a healthy weight are all associated with a lower risk of complications. Your doctor may also advise regular colonoscopy screening if appropriate for your age and overall risk profile.
Uncomplicated diverticulitis
Mild to moderate diverticulitis — without abscess, perforation, or fistula — is usually managed without surgery. Treatment typically includes rest, a liquid or low-fibre diet to allow the colon to recover, and antibiotics. Most people improve within a few days. After the episode resolves, a colonoscopy is usually recommended to confirm the diagnosis and rule out other conditions.
People who have had one episode of diverticulitis have a roughly 20-35% chance of having another. After a second episode, the risk of further recurrences increases. Your doctor will discuss whether any ongoing lifestyle changes or dietary adjustments are recommended to reduce that risk.
Complicated diverticulitis
Diverticulitis with complications — including a significant abscess, perforation, or a connection between the colon and another organ (called a fistula) — usually requires more aggressive treatment. A pericolonic abscess may be treated with antibiotics alone if it is small, or with image-guided drainage if it is larger. Perforation with peritonitis requires emergency surgery.
Some patients who have repeated episodes of diverticulitis, or whose symptoms significantly affect their quality of life, are offered elective surgery to remove the affected segment of the colon. This is called a colectomy or colonic resection, and it is usually curative for the affected section of bowel.
Colorectal cancer screening
Diverticular disease does not increase the risk of colon cancer. However, the symptoms of diverticular disease — including rectal bleeding, changes in bowel habits, and lower abdominal pain — can overlap with symptoms of colon cancer. For this reason, a colonoscopy is often recommended to look carefully at the colon lining and confirm that no other conditions are present.
Questions to ask your doctor
- Do I have diverticulosis, diverticulitis, or both?
- Was inflammation found, and if so, how severe was it?
- Were any complications found — such as an abscess or perforation?
- Do I need antibiotics or other medications?
- When should I have a follow-up colonoscopy?
- Are there changes to my diet or lifestyle that would reduce my risk of future episodes?
- Does the pathology report show anything else that needs follow-up, such as polyps?
- Should I be considered for surgery, and if so, when?
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