What Causes Diverticulitis?
Diverticulitis occurs when colonic diverticula (outpouchings in the colon wall) become inflamed and/or infected, typically developing in patients with pre-existing diverticulosis through a combination of structural weakness, increased intraluminal pressure, and inflammatory processes. 1, 2
Pathophysiologic Mechanism
The fundamental cause is herniation of colonic mucosa and submucosa through defects in the circular muscle layers of the colonic wall, typically at sites where blood vessels penetrate the colon. 3 This structural alteration creates "pockets" that can subsequently become inflamed or infected, progressing from diverticulosis (asymptomatic presence of diverticula) to diverticulitis (active inflammation). 4
- The inflammation develops when diverticula become obstructed or compromised, leading to bacterial overgrowth and inflammatory changes in the colonic wall and surrounding pericolic fat. 1
- Only 1-4% of patients with diverticulosis will develop acute diverticulitis in their lifetime, though approximately 5-10% of those with diverticulosis eventually experience this complication. 1, 2
Major Risk Factors
Non-Modifiable Risk Factors
- Age over 65 years is the strongest demographic risk factor, with prevalence increasing from 10% at age 40 to over 70% in elderly patients. 5, 6
- Genetic factors, particularly variants in the TNFSF15 gene, predispose to diverticular disease. 2
- Connective tissue disorders including polycystic kidney disease, Marfan syndrome, and Ehlers-Danlos syndrome increase risk. 2
Modifiable Risk Factors
- Obesity (BMI ≥30) significantly increases risk through mechanisms involving increased intra-abdominal pressure and chronic inflammation. 2, 7
- Smoking is a well-established modifiable risk factor that should be prioritized for cessation. 8, 3
- Alcoholism (not moderate consumption) increases incident diverticulitis risk. 8
- Medication use: NSAIDs, opioids, and corticosteroids all increase risk of developing diverticulitis. 2, 3
- Low dietary fiber intake has been classically linked to diverticular disease in Western populations, though recent studies have questioned the strength of this association. 5, 3
Comorbid Conditions
- Hypertension and type 2 diabetes are associated with increased risk. 2, 7
- Chronic conditions including cirrhosis, chronic kidney disease, and heart failure may predispose to more severe presentations. 2
Epidemiologic Context
The annual incidence in the United States is approximately 180 per 100,000 persons, resulting in 1.9 million outpatient visits and over 200,000 hospital admissions annually. 1, 2 Notably, the incidence in younger adults (40-49 years) increased by 132% from 1980 through 2007, indicating this is no longer exclusively a disease of the elderly. 1
Clinical Pitfalls
- Inadequate dietary fiber remains the most commonly cited environmental cause in Western populations, though the relationship is more complex than previously understood. 5, 3
- Recent evidence challenges older assumptions about nuts, seeds, and popcorn causing diverticulitis—these restrictions are no longer recommended. 3
- Alterations in colonic microbiota composition are increasingly recognized as contributing factors, though this remains an area of active investigation. 7