What Are Diverticula?
Diverticula (one is called a diverticulum) are small pockets or pouches that form in the wall of your colon — your large intestine. Picture a tiny bubble pushing outward through a weak spot in the bowel wall. That is a diverticulum. When you have several of them, that is called diverticulosis.
These weak spots tend to appear where small blood vessels pass through the bowel wall. Over many years, if you are eating a low-fibre diet, your stools become small and hard, and your bowel has to work harder — squeezing with more force — to move them along. That repeated pressure slowly pushes the inner lining of the bowel through those weak points, forming the pouches.
Worth knowing: these pouches are sometimes called "false" diverticula because they only contain the inner lining of the bowel, not the full thickness of the wall. That is why, in rare cases, they can get into trouble if pressure builds up inside them.
How Common Is Diverticular Disease?
Diverticular disease is extremely common in Western countries like Australia. It is rare in parts of the world where people eat a naturally high-fibre diet — which tells us a lot about why it happens here.
In Australia:
- Approximately 1 in 10 people over 40 have diverticula
- Around half of all people over 70 are affected
- By age 85, most people have diverticula
- The great majority — about 80% — will never get symptoms from them
- Only about 1 in 5 people with diverticula will ever develop diverticulitis (an inflamed or infected pouch)
So if you have just been diagnosed, the most likely story is that your diverticula will sit quietly in your bowel wall and never cause you a day of trouble. That is not us being falsely optimistic — it is genuinely what the numbers show.
Where Do Diverticula Develop?
In most Australians, diverticula form in the sigmoid colon — the S-shaped section of your large intestine that sits in your lower left abdomen, just above the rectum. It is the narrowest part of the bowel, which means it works the hardest and builds up the most pressure — so it is the most common place for pouches to form.
Pouches can also appear in other parts of the colon — higher up on the left side, across the middle, or on the right side. Right-sided diverticular disease is more common in people of Asian background and tends to occur at a younger age. Diverticula do not form in the rectum, which has a stronger, different type of muscle wall.
Diverticulosis vs Diverticulitis: Key Differences
Diverticulosis
- You have diverticula (pouches) but they are not inflamed or infected
- Most people feel nothing at all — it is often found by chance on a scan or colonoscopy
- Some people notice mild bloating or a change in their usual bowel pattern
- Occasionally a pouch can bleed, causing painless rectal bleeding
- No treatment needed — a high-fibre diet is all that is recommended
- Very common as you get older
Diverticulitis
- One or more of your pouches has become inflamed or infected
- Causes pain in the lower left abdomen, fever, nausea, and sometimes vomiting
- Can be straightforward (uncomplicated) or more serious if an abscess or perforation develops
- Diagnosed with a CT scan
- Treatment ranges from rest and antibiotics at home to hospital admission or, rarely, surgery
- Happens to about 1 in 5 people who have diverticulosis
How Does Diverticulitis Develop?
Doctors are still piecing together exactly why diverticulitis happens, but the most likely explanation is this: a small amount of stool gets stuck inside one of the pouches and hardens. The pressure and irritation cause a tiny break in the pouch wall, which triggers an infection or inflammation at that spot. Your body responds by fighting it — which is what causes the pain, fever, and tenderness you feel.
Diverticulitis comes in two forms:
- Uncomplicated: Inflammation that stays contained — no abscess, no perforation, no spread. This is by far the most common type, and many people manage it at home with antibiotics and a short period of rest.
- Complicated: The infection has spread or caused a secondary problem — such as an abscess (a pocket of pus), a perforation (a small hole in the bowel), a fistula (an abnormal channel connecting the bowel to another organ like the bladder), or a blockage from scarring. This type usually needs hospital treatment and sometimes surgery.
Symptoms and Presentation
Most people find out they have diverticulosis by accident — the pouches show up on a colonoscopy done for bowel cancer screening, or on a CT scan done for something completely unrelated. At that point, you have no symptoms and need nothing beyond some dietary guidance.
When diverticulitis does strike, the typical signs are:
- Pain in the lower left abdomen — usually a constant dull ache, though it can come in waves or be quite severe
- Fever — often mild, but higher if an abscess or perforation has developed
- Nausea and loss of appetite
- Change in bowel habit — constipation is common during an attack, but diarrhoea can also happen
- Urinary symptoms — if the inflamed section of bowel is lying close to the bladder, you might notice stinging when you urinate or need to go more often than usual
Sometimes a diverticulum bleeds without any infection — this is called diverticular bleeding. It feels very different: there is no pain, but you notice bright red or dark maroon blood when you go to the toilet. It can look alarming. The good news is that it stops on its own in most cases, though heavy or ongoing bleeding needs assessment in hospital.
Diagnosis
If your doctor suspects diverticulitis, the most useful test is a CT scan of your abdomen and pelvis with contrast dye. This gives a very clear picture of exactly what is happening — confirming the diagnosis, showing whether any complications like an abscess or perforation are present, and helping decide on the best treatment.
Blood tests are also taken. These usually show an elevated white cell count and a raised CRP (C-reactive protein) — both are markers of infection and inflammation, and they help your doctors track how well you are responding to treatment.
You will not have a colonoscopy during an acute attack. Putting air into an inflamed, tender bowel would be both uncomfortable and potentially risky. Instead, a colonoscopy is usually arranged six to eight weeks after you have fully recovered from your first episode. The main reason for this is to rule out bowel cancer, which occasionally looks similar to diverticulitis on a CT scan. It is a precautionary step — not a reason to panic.
Risk Factors
The good news here is that most of the factors linked to developing diverticula are things you have some control over. They include:
- Low dietary fibre: The single biggest dietary factor — when your diet is low in fibre, your stools are smaller and harder, and your bowel has to strain harder to move them along. That repeated pressure, over many years, is what forms the pouches.
- Carrying excess weight: Particularly weight around the middle, which increases pressure in the abdomen and affects how the gut works
- Being inactive: A sedentary lifestyle slows down how quickly food moves through your bowel
- High red meat intake: Several large studies have found a link between eating a lot of red meat and a higher risk of diverticulitis specifically
- Smoking: A more modest but consistent risk factor across the research
- Regular use of anti-inflammatory painkillers: Medications like ibuprofen or naproxen (NSAIDs) taken regularly appear to increase the risk of both diverticulitis and diverticular bleeding — if you take these often, it is worth discussing with your GP
- Getting older: Diverticula accumulate over time, and the bowel wall naturally becomes less elastic with age — this is why it is so much more common over 60
Frequently Asked Questions
Unfortunately not — once a pouch has formed, it does not disappear. But that is not as bad as it sounds, because the majority of diverticula never cause any symptoms at all. Eating more fibre and drinking plenty of water will not get rid of the pouches you already have, but they do help prevent new ones from forming and reduce your chance of ever getting diverticulitis.
No — they are related but different. Diverticular disease is the umbrella term for having diverticula at all. Diverticulitis specifically means one or more of those pouches has become inflamed or infected. Most people with diverticular disease have the quiet, symptom-free version (diverticulosis) and will never experience diverticulitis.
There does seem to be a modest genetic component — if a close family member has had it, your risk is slightly higher. But genes are far less important than your diet, lifestyle, and age. This is not like some hereditary bowel cancer syndromes where a single gene mutation causes the condition. Mostly, this is about how the bowel responds to decades of what we eat and how we live.
An abscess is a pocket of pus that forms around an inflamed diverticulum — your body trying to contain the infection. Small abscesses (under about 3–4 cm) often clear with antibiotics alone. Larger ones usually need draining, which is done by a radiologist using a CT scan as a guide to pass a thin drain through the skin into the abscess. This sounds worse than it is — it is done under local anaesthetic and relieves the pain quite quickly. Surgery is only needed in a minority of cases.
Most people with diverticular disease never need surgery. Surgery tends to come into the conversation if you have had a serious complication like a perforation or an abnormal connection between the bowel and another organ (a fistula), if your attacks keep coming back and are affecting your quality of life, or if you are not getting better from an acute episode. Your colorectal surgeon will go through the options with you based on your specific situation — there is no one-size-fits-all answer.
Yes — and you should actively aim for a high-fibre, varied diet. If you were told years ago to avoid nuts, seeds, and popcorn, that advice has been overturned. Current evidence does not support those restrictions. In fact, the best thing you can do for your bowel long-term is eat plenty of vegetables, fruit, legumes, and wholegrains. Your bowel will thank you.
Have questions about your diagnosis?
It is completely understandable to want clear answers after a diagnosis like this. Mr Ba Nguyen is a specialist colorectal surgeon who sees patients with diverticular disease regularly and can walk you through exactly what your situation means and what — if anything — needs to happen next. A GP referral is required. Call (03) 9816 3951 or email admin@northeasternsurgical.com.au.