Diverticulitis is common, generally presenting in patients of middle age and older, and has a wide variety of presentations. Although most cases of acute diverticulitis resolve spontaneously or with minimal intervention, some patients will require more complex intervention, including surgery.

The complications of diverticulitis include haemorrhage, stricture and obstruction, perforation, abscess formation, and fistulation into adjacent organs such as the bladder or vagina.

Defining diverticular disease

Diverticulosis is the term used to describe multiple diverticula, which are blind-ended out-pouching of mucosa that communicate with the lumen of the large bowel, usually located in the sigmoid and descending colon. Diverticulitis, or diverticular disease, refers to any condition causing symptoms secondary to colonic diverticulae.

Colonic diverticulosis is common in developed countries and can affect up to two-thirds of the elderly population, most of whom will remain asymptomatic. Epidemiological studies have suggested that an individual's risk of developing diverticulosis approaches 50% by the age of 60 years,¹ and 65% in those aged 70 years and older.² It is virtually unheard of in the first two decades of life.

Causes of diverticular disease

The underlying features of colonic diverticulosis are points of weakness within the colonic wall and increased intraluminal pressure. The disease process that leads to muscular hypertrophy appears to be related to lack of dietary fibre.

Low-fibre diets tend to distend the colon to a lesser extent and thereby require a greater luminal pressure to achieve motility. This factor is deemed to be the main reason behind the observation that diverticulosis is more prevalent in those following a Western diet and extremely rare in the developing world. Right-sided diverticulosis, although rare, appears to be the more prevalent pattern in the developing world. The underlying cause for this is not yet clearly identified.³

In fact, two distinct forms of diverticulosis may exist: one discernible by muscle thickening, mainly in the left colon, and associated with perforation and diverticulitis; the other caused by a diffuse connective tissue abnormality, resulting in pancolonic diverticulosis and a propensity for bleeding.^4,5 This possibility may partly account for the anatomical differences described between patients in Europe and the United States and those from Asian and African populations. It appears that this trait is acquired in migrant populations who adopt a "Western" lifestyle and individuals subsequently acquire similar risks as those in developed countries.⁶

The process of diverticulitis is thought to be secondary to the obstruction of diverticulae by faeces or mucus, or mucosal erosion within the diverticulae. The following factors are associated with diverticular disease:

• Low-fibre diet

• Cigarette smoking

• Adult polycystic kidney disease

• Immunosuppressant therapy.

Preventative measures

Few studies have clearly shown the link between lack of fibre in the diet and the development of diverticular disease, and no controlled trials have been carried out.⁷ Certainly, following a high-fibre diet will pose no harm, and most clinicians advise this.

A small number of studies have considered the use of probiotics in the prevention of diverticular disease.⁸ Theoretically, probiotics may stimulate the immune system and prevent chronic inflammation in diverticular disease, but evidence to support their use is lacking. The strains with beneficial properties most frequently belong to the genera Bifidobacterium and Lactobacillus, but other bacterial strains have been used, including certain strains of Escherichia coli and non-bacterial organisms such as Saccharomyces boulardii.

Anticholinergic drugs and calcium channel blockers may cause relaxation of the affected segment of colon; however, there is not enough evidence that the benefits of these pharmacological agents outweigh the potential side-effects.

Mesalazine is proposed to reduce chronic inflammation in the colon, and clinical trials have shown that it has some benefit in relieving symptoms in diverticular disease and may prevent recurrent attacks.⁹ A broader evidence base is required to support the widespread use of mesalazine, but it is a promising prospect for the future.

Clinical features

Presentation is variable, depending on the effects of the inflammation. Commonly, there is lower abdominal pain, typically localised to the left iliac fossa, and often associated with fever and general malaise. Symptoms are generally of gradual onset and the patient may experience altered bowel habit accompanied by rectal bleeding. Sudden-onset abdominal pain may signify perforation.

Less commonly, patients may present with rectal bleeding or signs of a colovesical fistula.

Initial management

In mild or uncomplicated cases it is appropriate to commence oral antibiotics with Gram-negative and anaerobic cover (such as an oral cephalosporin and metronidazole) and monitor the patient closely for improvement.

The requirement for referral to hospital is determined by the degree of abdominal tenderness, physiological parameters, the ability to maintain oral intake, comorbid conditions and failure to respond to oral antibiotics. The decision needs to be taken on an individual patient basis.

Initial conservative measures in hospital involve oxygenation, intravenous fluids and resuscitation.

Bowel rest (restriction to clear oral fluids or nil-by-mouth regimens), analgesia and intravenous antibiotics are the primary treatment. Most clinicians advocate treatment with metronidazole (500 mg intravenously, three times per day) for anaerobic organisms, and an intravenous cephalosporin to cover aerobes such as coliforms and enterococci. Gentamicin is often added in cases of major sepsis but the benefit is not proven. Antibiotic treatment should be continued for 7-10 days.

In some 85% of patients, a first episode of diverticulitis will resolve with conservative measures. The remainder will require some form of intervention, usually surgery or radiological drainage.^10-12

Investigations

If managing only mild symptoms of clinically uncomplicated diverticulitis there may be no indication for imaging. In more severe cases and in patients with potential complications, computed tomography (CT) scanning is the imaging modality of choice in the acute presentation,¹³ having a sensitivity of 97% and specificity of 100%.^14,15

CT scanning indicates the severity of disease and any complications, such as abscess formation, perforation or fistulation, and also plays a valuable role in the percutaneous drainage of collections.

Barium enema is the preferred imaging modality in assessing non-acute diverticular disease, and it is highly specific. It is less useful for acute cases, having a sensitivity of only 82% and a specificity of 81%.¹⁵

Emergency intervention

Diverticulitis requiring surgical intervention usually manifests as generalised peritonitis, sepsis or evidence of perforation and requires a decision on whether to operate from the surgical team. In some cases, when surgery is not immediately necessary, CT-guided drainage of pericolic or pelvic abscesses may be beneficial.

For patients requiring surgical intervention, laparotomy is almost always the first procedure. The stability of the patient, the nature of the disease, degree of intra-abdominal contamination and the expertise of the surgeon will determine which surgical procedure will follow.

Three procedures are in common use in surgical practice:

• Hartmann's procedure

• Exteriorisation and resection with colostomy and mucous fistula (Mikulicz procedure)

• Primary anastomosis (with or without defunctioning ileostomy).

Hartmann's procedure

Hartmann's procedure involves mobilising and resecting the area of diseased bowel. A colostomy is formed from the proximal bowel and the distal rectal stump is cross-stapled or oversewn and may be marked with a nylon stitch or brought out as a mucous fistula.

Mikulicz procedure

Mikulicz procedure involves side-by-side exteriorisation of the perforated segment as a sigmoid colostomy and mucous fistula. This technique is rarely performed as it confers little benefit over sigmoid resection.

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Hartmann's and Mikulicz procedure each carry an operative mortality of approximately 12% (see table 1, above); but they are employed when there is concern over forming an anastomosis in unprepared colon.

Primary anastomosis

If operative conditions are favourable, it may be possible to perform a primary anastomosis following resection of the affected colon. On-table colonic lavage of the proximal and distal bowel is carried out to reduce contamination at the anastomosis site, and colonic continuity is then re-established using a hand-sewn or stapled method. Many surgeons will fashion a proximal defunctioning stoma to protect the distal anastomosis in case of leakage. Primary anastomosis has been shown to achieve the lowest mortality and has the obvious benefit of removing the requirement of a subsequent laparotomy if the procedure is reversed.

A recent systematic review of Hartmann's procedure and primary anastomosis found an operative mortality rate of 19.6% for Hartmann's procedure compared with a mortality of 9.9% and anastomotic leak rate of 13.9% in primary anastomosis.¹⁶ These findings must be interpreted carefully as the data may represent different patient groups.

Laparoscopic methods have many advantages and are becoming more common in colorectal surgery, particularly for elective resection. However, there are as yet no studies comparing open and laparoscopic methods in perforated disease.

Referral for elective surgery

Diverticulitis occurs in 20-30% of patients with diverticulosis.^10,17 For most patients who respond satisfactorily to conservative treatment, any decision about their ongoing management will be based on the likelihood of recurrence and subsequent complications balanced against the morbidity and mortality of elective sigmoid resection.

While the risk of recurrence after resolution of a first attack is 2% per annum,¹⁸ the global risk of recurrence is reported as approximately

20-30%.^10-12 Recurrent attacks are less likely to respond to medical treatment and have a higher mortality rate;^11,12 therefore many bodies agree that elective resection may be indicated after two or more attacks of uncomplicated diverticulitis in a fit patient.^1,17,19

There is a subgroup of patients who require special consideration. Diverticulitis is uncommon in patients younger than 50 years, but when it does occur it seems to be most prevalent in obese young men. Patients in this subgroup who present with diverticulitis at a younger age appear to encounter more complications and are more likely to require surgery.^20,21 This may result from a more aggressive disease process and these patients tend to re-present more frequently after an initial attack of diverticulitis. It may be appropriate for prophylactic sigmoid colectomy to play a greater role in the management of these patients.

The surgeon must tailor his approach to the patient, with a lower threshold in younger patients with severe disease than in elderly patients with co-morbidities, because elective surgery carries significant potential mortality and morbidity.