Most Common Mucosa in Diverticula
Colonic diverticula contain mucosa and submucosa only—they are pseudodiverticula (false diverticula) that lack the muscularis propria layer, consisting of herniated mucosa and submucosa that protrude through weak points in the colonic muscle wall. 1, 2
Structural Composition
- Diverticula are outpouchings composed of mucosa bounded by muscularis mucosae and invested with a thin layer of submucosa, forced through defects in the circular muscle layers of the colonic wall 3
- The herniation occurs specifically at sites where nutrient vessels penetrate the muscularis propria, creating natural weak points in the muscle coat 4, 3
- The tips of these pseudodiverticula end in the colonic subserosa, with no true muscular layer present in the diverticular wall itself 3
Mucosal Characteristics in Uncomplicated Diverticulosis
The mucosa within diverticula exhibits several characteristic changes even in uncomplicated disease:
- Increased lymphoid infiltrate and development of lymphoglandular complexes are common findings 3
- Mucin depletion, mild cryptitis, and architectural distortion frequently occur within the diverticular mucosa 3
- Paneth cell metaplasia and ulceration may be present in the diverticular mucosa 3
Clinical Distinction: True vs. Pseudodiverticula
- True diverticula (containing all layers of the colonic wall including muscularis propria) are rare in the colon 2
- The vast majority of colonic diverticula are pseudodiverticula, which is the defining characteristic that distinguishes them from true diverticula found elsewhere in the gastrointestinal tract 1, 2
Important Caveat: Segmental Colitis Associated with Diverticulosis (SCAD)
- In approximately 1% of cases, the mucosa in diverticular segments may show features indistinguishable from ulcerative colitis or Crohn's disease, termed SCAD 5, 6, 3
- SCAD is defined as chronic inflammatory process confined to the diverticular segment, almost exclusively affecting the sigmoid colon, with normal rectum and proximal colon 5, 6
- This represents a diagnostic pitfall, as the mucosal changes are confined to the area of diverticulosis, and histologic evaluation of the rectum and proximal bowel is essential for differential diagnosis 3