Understanding Diverticular Disease

Introduction

What is diverticular disease?

Diverticular disease is a condition, first described in the nineteenth century, that mainly affects the large intestine (colon). Along the wall of the large intestine there are natural points of weakness at sites where blood vessels penetrate; these can form a sac-like protrusion or pouch through the muscle wall known as a ‘diverticulum’. More than one diverticulum is referred to as ‘diverticula’. These diverticula develop over a period of time. Individuals can have any number of diverticula and the extent of colonic involvement is variable, although in most cases the lower left colon is likely to be involved (known as the sigmoid colon).

Terminology

The terms used in diverticular disease can be confusing and need clarification:

• Diverticulosis: the presence of diverticula that are asymptomatic
• Diverticular disease: diverticula that are associated with symptoms
• Diverticulitis: evidence of diverticular inflammation with or without localised symptoms and signs
• Complicated diverticulitis: perforation, abscess, fistula, stricture/obstruction.

How common is diverticular disease?

Approximately 50 per cent of those aged over 50 years will have diverticulosis and 70 per cent will have developed diverticula by the time that they are aged 80.

What is the colon?

The colon or large intestine is a part of the digestive system responsible for the formation of stools. It averages one metre in length. The colon reabsorbs water back into the bloodstream, causing the stools to firm up. It also helps with passage of the stools through waves of contractions called ‘peristalsis’ so that they can be eliminated through your back passage (anus). The end of the large intestine is divided into three parts: the descending colon, sigmoid colon and rectum. The rectum acts as a storage site for stools. Of note, the sigmoid colon is the narrowest part of the bowel and this is the site where the pressure generated is the highest.

Where does diverticular disease occur?

Diverticular disease typically affects the descending and sigmoid colon, which lies on the left side of your stomach. Although diverticula can form in any part of the digestive system, this is rare. In Asian populations, right-sided diverticular disease is more common, probably due to genetic differences.

Who gets diverticular disease?

Diverticular disease is highly prevalent in western countries and rare in the developing world. It is believed that one of the biggest risk factors for diverticular disease is a low-fibre diet, especially insoluble fibre found in fruit and vegetables, which is more common in the west. The lack of dietary fibre reduces the volume of stool in the bowel, which means that the pressure of the bowel contractions is passed on to the bowel wall rather than the bowel contents. This causes pouches to ‘pop out’ at points of natural weakness in the bowel wall where the arterial blood supply passes through gaps in the muscle layers.
The risk of diverticular disease increases with age and is not very common before the age of 40 (less than 10 per cent of all cases), increasing in prevalence to more than 40 per cent in patients aged over 70 years. The condition affects men and women equally; however, it is slightly more common in women over who are aged over 70 years. There also appears to be a genetic contribution, so you are more likely to develop diverticular disease if your family members have it. Patients who are obese are also at increased risk and this is often associated with diverticular disease in younger patients.

Causes of diverticular disease

A low-fibre diet poses a higher risk of diverticular disease; similarly, a diet rich in fatty foods and red meat increases the risk. Certain conditions predispose to the formation of diverticula including disorders of bowel movement (motility) and collagen disorders such as Marfan’s syndrome.