What is the pathophysiology and appropriate management of diverticulitis in an adult patient?

Pathophysiology of Diverticulitis

Anatomical and Structural Basis

Diverticula form at points of relative weakness in the colonic wall where the vasa recta penetrate the circular muscle layer to supply the mucosa, most commonly occurring along the mesenteric side of the antimesenteric taeniae in parallel rows. 1

• The outpouchings represent herniation of mucosa and submucosa through the muscular layer at these anatomically vulnerable sites 1
• In Western populations, diverticula predominantly affect the sigmoid and descending colon, while right-sided involvement is more common in Asian populations due to dietary and genetic factors 1
• Approximately 50% of individuals over age 60 and more than 60% over age 80 develop colonic diverticula 1

Progression from Diverticulosis to Diverticulitis

The exact mechanism by which diverticulosis progresses to diverticulitis remains incompletely understood, but only 1-4% of patients with diverticulosis will develop acute diverticulitis in their lifetime. 2, 1

• The traditional theory of fecalith obstruction causing microperforation has been challenged by emerging evidence 3
• Current understanding emphasizes a multifactorial process involving chronic low-grade inflammation, alterations in gut microbiota (dysbiosis), and genetic predisposition including variants in the TNFSF15 gene 2, 3
• Mucosal injury at the neck or dome of the diverticulum triggers an inflammatory cascade that can remain localized (uncomplicated) or progress to complications 3

Inflammatory Process and Disease Spectrum

Diverticulitis represents a spectrum from localized inflammation (uncomplicated) to inflammation with abscess formation, perforation, fistula, obstruction, or bleeding (complicated). 4

• Uncomplicated diverticulitis (85-88% of cases) involves inflammation limited to the colonic wall and immediately surrounding pericolic tissue without abscess, perforation, or other complications 2, 5
• Complicated diverticulitis (12-15% of cases) includes abscess formation, phlegmon, free perforation with purulent or feculent peritonitis, fistula formation (most commonly colovesical), stricture, or obstruction 4, 2
• The inflammatory response triggers increased C-reactive protein levels, leukocytosis, and systemic symptoms including fever when the process extends beyond localized inflammation 5

Risk Factors and Pathogenic Contributors

Multiple modifiable and non-modifiable factors increase the risk of both diverticulosis formation and progression to diverticulitis. 2, 1

• Age over 65 years represents the strongest demographic risk factor, with prevalence increasing progressively with advancing age 2
• Genetic factors account for approximately 50% of diverticulitis risk, including connective tissue disorders (Marfan syndrome, Ehlers-Danlos syndrome, polycystic kidney disease) 6, 2
• Medications that increase risk include NSAIDs (which may impair mucosal healing), opioids, and corticosteroids (which increase perforation risk) 6, 2, 1
• Metabolic factors include body mass index ≥30 kg/m², hypertension, and type 2 diabetes 2
• Lifestyle factors include smoking, sedentary behavior, and low dietary fiber intake 1

Clinical Presentation Patterns

Acute diverticulitis typically presents with left lower quadrant pain accompanied by fever, leukocytosis, and elevated inflammatory markers, though presentation varies based on disease severity and patient factors. 2, 5

• Associated symptoms include nausea, vomiting, anorexia, altered bowel habits (constipation or diarrhea), and dysuria when inflammation involves the bladder 5
• Immunocompromised patients may present with milder signs and symptoms despite more severe underlying disease, making clinical assessment unreliable in this population 7
• Physical examination reveals left lower quadrant tenderness, though the absence of peritoneal signs does not exclude complicated disease 5

Complications and Natural History

Contrary to older paradigms, the natural history of diverticulitis is not necessarily progressive, and recurrence rates are lower than historically believed. 1

• Among patients with an index episode, the 10-year recurrence rate is approximately 22%, increasing to 55% after a second episode 4
• The risk of complicated diverticulitis is highest with the first presentation rather than with recurrent episodes 6
• Emergency surgery rates reach 39.3% in immunocompromised patients, with postoperative mortality of 31.6% in this population 7
• Only 15-30% of patients admitted with acute diverticulitis require surgical intervention during that admission 5