What is diverticulitis?

What is Diverticulitis?

Diverticulitis is inflammation and/or infection of diverticula (outpouchings of the intestinal wall), most commonly occurring in the sigmoid colon, affecting approximately 180 per 100,000 people annually in the United States. 1, 2

Pathophysiology and Definition

Diverticulitis develops when diverticula—structural outpouchings formed by herniation of colonic mucosa and submucosa through defects in the circular muscle layer—become inflamed or infected. 2, 3 These outpouchings typically form at sites where blood vessels penetrate the colonic wall, creating areas of relative weakness. 4

• Only 1-4% of patients with diverticulosis (the presence of diverticula) will develop acute diverticulitis in their lifetime, though some estimates suggest 5-10% may be affected. 1, 2, 4
• The condition represents a painful gastrointestinal disease that can recur unpredictably and lead to chronic symptoms. 5

Epidemiology and Burden

The disease carries substantial healthcare impact:

• Results in more than 1.9 million outpatient visits and 208,000 inpatient admissions annually in the United States. 1
• Financial burden exceeds $5.5-6.3 billion annually. 1, 2
• The incidence in younger adults (40-49 years) increased by 132% from 1980 through 2007, indicating a shifting demographic pattern. 1

Risk Factors

Multiple modifiable and non-modifiable factors contribute to diverticulitis risk:

• Age-related: Prevalence increases dramatically with age, affecting over 50% of people over age 60 and over 60% of those over age 80. 4
• Genetic factors: Variants in the tumor necrosis factor superfamily member 15 (TNFSF15) gene contribute to disease susceptibility. 2
• Lifestyle factors: Obesity (BMI ≥30), smoking, sedentary lifestyle, and use of NSAIDs, opioids, and corticosteroids all increase risk. 2, 4
• Medical conditions: Hypertension, type 2 diabetes, and connective tissue diseases (polycystic kidney disease, Marfan syndrome, Ehlers-Danlos syndrome) are associated with increased risk. 2

Clinical Classification

Diverticulitis is categorized into two main types:

Uncomplicated Diverticulitis (85-88% of cases)

• Involves thickening of the colon wall and peri-colonic inflammatory changes without abscess, perforation, stricture, or fistula formation. 1, 2

Complicated Diverticulitis (12-15% of cases)

• Defined by the presence of localized or generalized perforation, abscess formation, fistula, stricture, or obstruction. 1, 4

Clinical Presentation

The hallmark symptom is acute or subacute left lower quadrant abdominal pain, though presentation varies:

• Fever, changes in bowel habits (constipation or diarrhea), nausea, and vomiting are common accompanying symptoms. 1, 6
• Laboratory findings typically include elevated white blood cell count and/or C-reactive protein (CRP). 1
• Clinical suspicion alone is correct in only 40-65% of cases, making imaging essential for confirmation. 6

A critical caveat: The risk of complicated diverticulitis is highest with the first presentation, not with recurrent episodes as previously believed. 5, 1 This challenges older paradigms that assumed progressive disease with each recurrence.

Diagnostic Approach

CT scan of the abdomen and pelvis with oral and intravenous contrast is the gold standard diagnostic test:

• Sensitivity: 95-99% 1, 6
• Specificity: 99-100% 6, 2
• Typical findings include thickening of the colon wall and increased density of pericolic fat. 1

This high diagnostic accuracy makes CT imaging essential when diverticulitis is suspected, as clinical examination alone is insufficient for reliable diagnosis. 6

Underlying Mechanisms

Recent understanding has evolved beyond simple mechanical obstruction theories:

• Chronic low-grade inflammation, genetic alterations, and gut dysbiosis all contribute to disease pathophysiology. 3
• The exact mechanism by which diverticulosis progresses to diverticulitis remains incompletely understood, though inflammation and infection of the diverticula are central features. 7, 4