Definition/General
Introduction:
Diverticulitis is acute or chronic inflammation of colonic diverticula
Represents complication of diverticulosis
Characterized by mucosal inflammation and wall thickening
May lead to perforation, abscess, or stricture formation.
Origin:
Results from mechanical obstruction of diverticular neck
Leads to bacterial proliferation and inflammation
Shows microperforation of diverticular wall
Associated with increased intraluminal pressure
Western diet and lifestyle factors contribute.
Classification:
Acute diverticulitis: sudden onset inflammation
Chronic diverticulitis: recurrent episodes
Complicated diverticulitis: perforation, abscess, fistula
Uncomplicated diverticulitis: simple inflammation
Hinchey classification for severity.
Epidemiology:
Peak incidence in elderly population (>60 years)
Western countries: left-sided predominance
Asian countries: right-sided predominance
Increasing incidence in developing countries
Low fiber diet major risk factor.
Clinical Features
Presentation:
Left lower quadrant pain (Western pattern)
Right lower quadrant pain (Asian pattern)
Fever and leukocytosis
Change in bowel habits
Nausea and vomiting
Abdominal tenderness.
Symptoms:
Crampy abdominal pain (most common)
Fever (70-80% cases)
Constipation or diarrhea
Urinary symptoms (colovesical fistula)
Rectal bleeding (uncommon in diverticulitis)
Pneumaturia (fistula).
Risk Factors:
Advanced age (>50 years)
Low fiber diet
Obesity
Physical inactivity
Smoking
NSAIDs and steroids
Genetic predisposition.
Screening:
CT scan (diagnostic imaging)
Colonoscopy (after acute episode resolves)
Barium enema (contraindicated in acute phase)
Ultrasound (limited utility)
MRI (special circumstances).
Master Diverticulitis Pathology with RxDx
Access 100+ pathology videos and expert guidance with the RxDx app
Gross Description
Appearance:
Thickened bowel wall
Mucosal edema and hyperemia
Diverticular openings visible
Inflammatory exudate in diverticular sacs
Perforation sites (complicated cases)
Abscess formation.
Characteristics:
Segment shortening and wall thickening
Serosal inflammatory changes
Adhesions to adjacent structures
Fistula tracts (complicated disease)
Stricture formation (chronic cases)
Microperforation common.
Size Location:
Sigmoid colon (Western countries)
Cecum and ascending colon (Asian countries)
Pan-colonic involvement possible
Segmental distribution common
Skip areas may be present.
Multifocality:
Segmental involvement typical
Multiple diverticula in affected segment
Varying stages of inflammation
Recurrent episodes affect same segment
Progressive disease over time.
Microscopic Description
Histological Features:
Acute inflammatory infiltrate
Mucosal ulceration and necrosis
Transmural inflammation
Diverticular perforation
Abscess formation
Fibroblast proliferation (chronic cases).
Cellular Characteristics:
Neutrophilic infiltrate (acute phase)
Lymphocytes and plasma cells (chronic)
Macrophages and foreign body giant cells
Fibroblasts and myofibroblasts
Endothelial proliferation.
Architectural Patterns:
Diverticular sac involvement
Mucosal destruction
Wall thickening (muscular hypertrophy)
Serosal inflammatory reaction
Vascular congestion
Fibrosis (chronic stages).
Grading Criteria:
Mild: limited mucosal inflammation
Moderate: transmural inflammation, no perforation
Severe: perforation, abscess formation
Chronic: fibrosis, wall thickening
Complicated: fistula, stricture.
Immunohistochemistry
Positive Markers:
CD68 (macrophages)
CD3 (T lymphocytes)
CD20 (B lymphocytes)
Smooth muscle actin (myofibroblasts)
CD31 (endothelium).
Negative Markers:
Cytokeratin (lost in ulcerated areas)
Specific infectious agents (unless secondary infection)
Malignancy markers
Autoimmune markers.
Diagnostic Utility:
Excludes infectious etiology
Differentiates from IBD
Assesses inflammatory cell types
Evaluates vascular changes
Usually not required for diagnosis.
Molecular Subtypes:
Acute inflammatory (neutrophil-predominant)
Chronic inflammatory (lymphoplasmacytic)
Fibrotic (myofibroblast-rich)
Vascular (ischemic component).
Molecular/Genetic
Genetic Mutations:
No specific mutations identified
Polygenic predisposition
Connective tissue gene variants
Inflammatory pathway genes
Familial clustering reported.
Molecular Markers:
Inflammatory cytokines (IL-1β, TNF-α, IL-6)
Matrix metalloproteinases
Prostaglandins (COX-2)
Nitric oxide
Reactive oxygen species.
Prognostic Significance:
Age at first episode (younger age worse prognosis)
Complicated vs uncomplicated
Recurrence rate (20-30%)
Response to conservative management
Need for surgical intervention.
Therapeutic Targets:
Antibiotics (broad spectrum)
Anti-inflammatory agents
Bowel rest
High fiber diet (prevention)
Surgical resection (complications).
Differential Diagnosis
Similar Entities:
Appendicitis (right-sided diverticulitis)
Inflammatory bowel disease (Crohn disease)
Ischemic colitis
Infectious colitis
Colorectal carcinoma
Irritable bowel syndrome.
Distinguishing Features:
Diverticulitis: Diverticular involvement, segmental
IBD: Continuous inflammation, younger age
Ischemic: Watershed areas, older age
Infectious: Organisms identified
Carcinoma: Mass lesion, dysplasia.
Diagnostic Challenges:
Distinguishing from IBD (clinical correlation important)
Differentiating from ischemic colitis
Excluding malignancy (stricture cases)
Recognizing complications
CT findings crucial.
Rare Variants:
Right-sided diverticulitis (Asian populations)
Giant diverticulum
Diverticular bleeding (without inflammation)
Smoldering diverticulitis
Recurrent diverticulitis.
Sample Pathology Report
Template Format
Sample Pathology Report
Complete Report: This is an example of how the final pathology report should be structured for this condition.
Specimen Information
[specimen type] from [anatomical location]
Clinical Information
Clinical presentation: [symptoms]. Duration: [acute/chronic]
Gross Features
Wall thickening: [present/absent]. Diverticula: [number and condition]. Perforation: [present/absent]
Inflammatory Features
Acute inflammation: [mild/moderate/severe]. Transmural involvement: [present/absent]. Abscess formation: [present/absent]
Complications
Perforation: [present/absent]. Fistula: [present/absent]. Stricture: [present/absent]
Chronic Changes
Fibrosis: [present/absent]. Muscular hypertrophy: [present/absent]. Wall thickening: [mild/moderate/severe]
Malignancy Assessment
No evidence of dysplasia or malignancy identified
Final Diagnosis
[Acute/Chronic] Diverticulitis, [complicated/uncomplicated]