Diverticular disease and diverticulitis
Diverticula are small pouches that form in the wall of the colon. They are extremely common — present in a majority of people over sixty in Western countries — and in most they never cause any trouble at all. Having diverticula (diverticulosis) is not a disease. The clinical questions are when they become inflamed, how that inflammation should be treated, and — an area where practice has changed substantially and where outdated advice persists — when surgery is genuinely needed.
How they form
The colonic wall has an inherent weak point. The arteries supplying the mucosa, the vasa recta, penetrate the muscular layer to reach the inner lining, and each penetration leaves a small gap in the muscle. These gaps lie in rows between the mesenteric and antimesenteric taeniae coli.
When pressure inside the colon rises, the mucosa and submucosa are forced outward through these gaps. Because only the inner layers herniate, these are false diverticula — they have no muscle in their wall, which is why they are thin and why they can perforate.
The pressure is generated by segmentation: the colon contracts into closed segments to mix and propel its contents, and a low-fibre diet producing small, firm stools requires higher pressures to move them. The sigmoid colon, with the narrowest lumen and the highest pressures, is the commonest site by a wide margin — in accordance with Laplace's law, where pressure required rises as radius falls.
Age contributes: the colonic wall becomes stiffer, with altered collagen and elastin, and the muscle layer thickens and shortens. Connective tissue disorders such as Ehlers-Danlos and Marfan syndromes cause diverticula at a young age for this reason.
Notably, in Asian populations diverticula are typically right-sided, single and true diverticula — a different entity with a different natural history.
What causes diverticulitis
The traditional explanation — that a piece of food or a faecolith obstructs the neck of a diverticulum, causing it to become infected like an appendix — is now regarded as incomplete. Current understanding places more weight on chronic low-grade inflammation, alterations in the colonic microbiome, and micro-perforation of the thin diverticular wall, with the resulting inflammation contained to a greater or lesser degree by surrounding tissues.
This shift matters practically, because it explains why not all diverticulitis requires antibiotics, and it has dissolved the old advice about avoiding nuts and seeds, which has been shown not to increase risk.
Risk factors for developing diverticulitis include obesity, smoking, physical inactivity, a diet high in red meat and low in fibre, NSAIDs and opioids, and corticosteroids and immunosuppression — the last being important, since immunosuppressed patients present atypically and perforate more readily.
The spectrum of disease
- Diverticulosis — diverticula present, no symptoms. No treatment needed.
- Symptomatic uncomplicated diverticular disease — intermittent left iliac fossa pain, bloating and altered bowel habit without inflammation. Overlaps considerably with irritable bowel syndrome.
- Acute uncomplicated diverticulitis — inflammation confined to the colonic wall and immediately surrounding fat.
- Acute complicated diverticulitis — abscess, perforation with peritonitis, obstruction, or fistula. The Hinchey classification grades this from a confined pericolic abscess (I), through a pelvic abscess (II), to purulent peritonitis (III) and faeculent peritonitis (IV).
- Diverticular bleeding — a separate problem, caused by erosion of the vasa recta at the dome of a diverticulum, producing painless, often substantial, fresh rectal bleeding. It is a common cause of major lower gastrointestinal bleeding, and it stops spontaneously in the great majority.
- Segmental colitis associated with diverticulosis — inflammation of the mucosa between diverticula, resembling inflammatory bowel disease.
Symptoms
Acute diverticulitis:
- left lower abdominal pain, steady rather than colicky, usually building over a day or two — often described as "left-sided appendicitis"
- fever
- change in bowel habit — either constipation or diarrhoea
- nausea; vomiting suggests obstruction or ileus
- urinary frequency or urgency, from an inflamed sigmoid sitting on the bladder
- localised tenderness and guarding; a mass if an abscess has formed
Features indicating complications: generalised abdominal pain with rigidity (perforation); swinging fever and a mass (abscess); pneumaturia, faecaluria or recurrent urinary infections (colovesical fistula); passage of faeces per vaginam (colovaginal fistula); and vomiting with distension (obstruction).
How the diagnosis is made
- CT of the abdomen and pelvis with contrast is the investigation of choice. It confirms the diagnosis, grades severity, identifies abscess, free gas and fistula, and — importantly — excludes other causes. Clinical diagnosis alone is wrong in a significant minority.
- Blood tests — white count and C-reactive protein, which also guide severity.
- Colonoscopy is avoided in the acute phase because of the risk of perforation.
- Colonoscopy after recovery, typically at six to eight weeks, is recommended after complicated diverticulitis or a first episode with atypical features, principally to exclude a colonic cancer masquerading as diverticulitis. Routine colonoscopy after every uncomplicated episode confirmed on CT is no longer considered necessary in all cases.
Treatment
Acute uncomplicated diverticulitis
This is where practice has changed most. Randomised trials have shown that antibiotics are not required in all cases: immunocompetent patients with mild uncomplicated disease, without significant comorbidity, who can eat and drink, do as well with observation, fluids and analgesia alone. Antibiotics remain indicated for immunosuppressed patients, those with significant comorbidity, sepsis, or failure to improve.
Most patients are treated as outpatients with oral intake as tolerated, and improve within a few days.
Abscess
Small abscesses, generally under 3–4cm, usually resolve with antibiotics. Larger ones are treated by percutaneous radiological drainage, which resolves the acute problem in the majority and converts what was once an emergency operation into an elective one, or none at all.
Perforation with peritonitis
Requires emergency surgery. Options:
- Hartmann's procedure — resection of the diseased sigmoid with an end colostomy and closure of the rectal stump. The traditional operation, safe, but a substantial proportion of stomas are never reversed.
- Resection with primary anastomosis, with or without a protecting ileostomy — increasingly preferred in suitable, stable patients, with better rates of eventual stoma reversal.
- Laparoscopic lavage — washout without resection, for purulent peritonitis without a visible perforation. It has a role in selected patients but the trial results have been mixed, and it is used with care.
Elective surgery
This deserves clear statement, because the old rule — resect after two attacks — has been abandoned.
The decision is now individualised, based on the frequency and severity of episodes, the effect on quality of life, the patient's age and fitness, and immune status. The relevant considerations:
- Most patients who have a single episode never have another.
- The risk of a subsequent episode requiring emergency surgery is lower than was once believed; recurrent episodes tend to be no more severe than the first.
- Most perforations occur at the first presentation, so resecting after recurrent mild episodes does not prevent the catastrophe it was intended to prevent.
- Elective resection carries its own real risks, including anastomotic leak and persisting symptoms.
Accepted indications are: complicated disease such as fistula or stricture; recurrent episodes seriously affecting quality of life; immunosuppressed patients, who tolerate an episode badly; and inability to exclude malignancy.
Elective resection is laparoscopic where possible, removing the sigmoid colon and, importantly, joining healthy colon to the upper rectum — not to distal sigmoid — since leaving sigmoid behind is associated with recurrence.
Diverticular bleeding
Resuscitation, then CT angiography to localise the source if bleeding continues. Colonoscopy allows treatment with clips or adrenaline. Transcatheter embolisation is effective where bleeding persists. Surgery is rarely needed, and segmental resection requires the bleeding point to have been localised first.
Recovery and prevention
After an acute episode, symptoms usually settle within a week. A high-fibre diet, adequate fluids, physical activity, weight control and stopping smoking all reduce the risk of recurrence. Nuts, seeds, popcorn and small fruit pips do not need to be avoided — this long-standing advice has been shown to be unfounded, and patients are often relieved to hear it. NSAIDs and opioids are best avoided where possible.
After elective laparoscopic sigmoid resection, hospital stay is typically three to five days with enhanced recovery, and return to normal activity four to six weeks.
When to seek an opinion
Left-sided abdominal pain with fever requires assessment. Severe generalised abdominal pain, rigidity, or feeling very unwell requires emergency attention. So does significant rectal bleeding. Air or faecal material passed in the urine, or recurrent urinary infections in someone with known diverticular disease, should prompt referral, as these indicate a fistula.
Common questions
I was told I have diverticula. Is that serious?
In itself, no. Small pouches in the bowel wall are extremely common with age and most people who have them never have any trouble from them. It is a finding, not a disease, and it does not require treatment or a special diet.
Should I avoid nuts, seeds and popcorn?
No. This advice was given for decades on theoretical grounds and has since been studied properly — people who eat nuts and seeds do not have more attacks, and may have fewer. You can eat them.
Do I need antibiotics every time?
Not necessarily. For a mild attack in someone otherwise well, treatment with fluids, painkillers and observation works as well as antibiotics, and avoids their side effects. Antibiotics are important if you are unwell, have other significant medical problems, take medication that suppresses the immune system, or are not improving.
I have had two attacks. Do I need an operation?
Not automatically, and this represents a real change in thinking. The old rule of operating after two attacks has been abandoned, because most later attacks are no worse than the first and most serious complications happen at the very first episode. Surgery is advised where attacks are frequent and genuinely affecting your life, where there are complications such as a fistula or narrowing, or where your immune system is suppressed.
Will I need a bag?
Usually not. Planned operations for diverticular disease normally involve removing the affected segment and rejoining the bowel in one go. A stoma is much more likely when surgery is done as an emergency for a perforation, and even then it is often temporary.
Can diverticula go away?
No, the pouches themselves are permanent. But most cause no problems, and the aim of treatment is to prevent and manage inflammation rather than to remove the pouches.
I am bleeding heavily but I have no pain. Is that diverticular?
Painless, sudden, fairly heavy fresh rectal bleeding is a characteristic way diverticula bleed, from a small artery at the base of a pouch. It stops on its own in the great majority of cases, but it needs urgent assessment, because the amount of blood can be significant and other causes need excluding.
Can it be cancer instead?
Bowel cancer can occasionally cause a very similar picture on a scan, which is why a colonoscopy is recommended after recovery in certain situations — particularly after a complicated attack or where anything about the presentation is atypical. It is a precaution rather than an expectation.
Related conditions
Other conditions of the colon & rectum covered on this site:
- Colon cancer
- Rectal cancer
- Bowel polyps (colorectal polyps)
- Crohn's disease — the surgical perspective
- Ulcerative colitis — the surgical perspective
- Large bowel obstruction and volvulus
- Appendicitis
- Hereditary bowel cancer syndromes (Lynch syndrome and FAP)
This page provides general information and does not replace an individual medical consultation. Assessment and treatment are decided for each patient after review of their history, examination and investigations.