Why is the sigmoid colon the most common site for diverticulosis (diverticular disease)?

From the Guidelines

The sigmoid colon is the most common location for false diverticulosis due to its unique anatomical and physiological characteristics. The sigmoid colon experiences the highest intraluminal pressure during bowel movements compared to other parts of the colon, creating more force against the colonic wall 1. This segment has a smaller diameter than other parts of the large intestine, which according to Laplace's law, results in greater wall tension for a given pressure. Additionally, the sigmoid colon has a more complex arrangement of taeniae coli (muscle bands) and a thicker muscular layer, which creates natural weak points where blood vessels penetrate the muscle wall. These weak points become potential sites for diverticular formation.

Some key factors that contribute to the high incidence of false diverticulosis in the sigmoid colon include:

• High intraluminal pressure during bowel movements
• Smaller diameter compared to other parts of the colon
• Complex arrangement of taeniae coli and thicker muscular layer
• Western diets low in fiber, leading to smaller stool volume and higher pressure needed for propulsion through this region
• The sigmoid's position as the final segment before the rectum, bearing the burden of processing increasingly solid stool, requiring stronger contractions that further increase intraluminal pressure. As noted in a recent clinical practice update on medical management of colonic diverticulitis, patients should consume a high-quality diet to reduce the risk of recurrence 1.

The combined effects of these factors lead to herniation of the mucosa and submucosa through the muscular layer, forming the characteristic outpouchings of diverticulosis predominantly in the sigmoid colon. It is essential to consider these factors when managing patients with diverticulitis, as they can impact treatment outcomes and the risk of recurrence 1.

From the Research

Pathogenesis of Diverticulosis

• The exact pathogenesis of diverticular disease of the sigmoid colon is not well established 2
• However, the hypothesis that a low-fibre diet may result in diverticulosis and a high-fibre diet will prevent symptoms or complications of diverticular disease is widely accepted 2
• Pathogenesis is multifactorial and includes low-fibre diet, dysmotility, increased intraluminal pressure and morphological changes 3

Location of Diverticulosis

• Diverticula most commonly occur along the mesenteric side of the antimesenteric taeniae resulting in parallel rows 4
• These spots are thought to be relatively weak as this is the location where vasa recta penetrate the muscle to supply the mucosa 4
• The sigmoid colon is the most common site of colonic diverticulitis in Western countries 4

Risk Factors for Diverticulitis

• Risk factors for diverticular disease include use of NSAIDS, aspirin, steroids, opioids, smoking and sedentary lifestyle 4
• Higher consumption of red meat was associated with a mild increase in the risk of acute diverticulitis 5
• Higher fish intake was associated with a reduced risk of diverticulitis in an age-adjusted model 5

Prevalence of Diverticulosis

• Diverticulosis is one of the most common incidental findings on colonoscopy and the eighth most common outpatient diagnosis in the United States 4
• Over 50% of people over the age of 60 and over 60% of people over age 80 have colonic diverticula 4
• The lifetime risk of developing diverticulitis is estimated at 10–25% 4