Diverticular Colitis

Synonyms

Crescentic fold disease; Diverticular disease-associated chronic colitis; Isolated sigmoiditis; Segmental colitis associated with diverticulosis (SCAD)

Definition

Diverticular colitis can be defined operationally as mucosal inflammation within a colon segment containing diverticula. It primarily affects the sigmoid colon. It is however distinct from diverticulitis, which is inflammation of one or more diverticula and the surrounding connective and muscle tissues. Diverticular colitis is noteworthy for mimicking chronic inflammatory bowel disease (IBD), both endoscopically and histologically.

Clinical Features

• Incidence

  Only a subset of patients with diverticulosis coli also develops diverticular colitis. Estimates vary between less than 1% and 4%. The true incidence and prevalence are probably underestimated as many patients do not develop worrisome symptoms. The most common presenting complaints are cramping left lower quadrant pain or tenesmus, constipation or diarrhea which may be mucous, and rectal bleeding. The classic radiologic exam shows only diverticular disease. The preferred diagnostic technique is endoscopy with biopsies.

• Age, Sex

  Similar to diverticulosis, diverticular colitis is mainly a disease of elderly persons.

• Site

  The inflammation is limited to the diverticular segment of the bowel. Diverticular colitis typically involves the mucosa between the diverticular ostia and only occasionally spreads to the diverticula proper (although without erosions or large numbers of neutrophils). In contrast, diverticulitis always involves the diverticula and their ostia, and may spread to the surrounding mucosa, but only when severe.

• Treatment and Outcome

  Diverticular colitis may be treated conservatively with the same measures as for diverticular disease (e.g., a high-fiber diet and antibiotics when needed). It also responds to treatment with 5-aminosalicylic acid (5-ASA) compounds, with over half of the patients achieving clinical remission. In most cases, the clinical course is benign and self-limited, although some patients may require sigmoid colectomy for bleeding or stricture complications. An increased risk for diverticulitis or colon cancer seems to be remote.

Macroscopy

At endoscopy, the lesions are typically situated in the sigmoid. In addition to diverticula, one sees mucosal erythema, friability, and erosions. This pattern can be very similar to the one observed with ulcerative colitis (UC). Also linear ulcerations in a longitudinal pattern and a cobblestone appearance may be present, causing confusion with Crohn’s disease (CD). Clues to the correct diagnosis are that the inflammation is limited to the diverticular colon segment, and that the rectum is characteristically spared.

Microscopy

The pathogenesis of the mucosal inflammation has been ascribed to abnormal prominence of mucosal folds with chronic or recurrent mucosal prolapse, ischemia, and inflammation. Abnormal exposure to luminal antigens and toxins in a context of altered bowel flora due to stasis has also been implicated. Finally, the mass effect of peridiverticulitis and serosal abscesses may play a role (although it has been observed that diverticular colitis can develop even before the diverticula themselves are well formed).

Biopsies should be taken from the most inflamed-looking mucosa, preferably at some distance from the diverticular ostia. The endoscopist should warn the pathologist that the biopsies are taken from a diverticular colon segment. Preferably, rectal biopsies should be taken for microscopic examination to rule out inactive or previously treated UC. When mucosal biopsies are taken from areas between the diverticular openings, the histological aspect may mimic IBD to perfection. There are two patterns, one with diffuse and the other with patchy mucosal disease, potentially causing confusion with UC or CD, respectively.

In the first form, there is widespread architectural disturbance with crypt branching and shortening, together with the presence of an evenly spread, dense mononuclear cell infiltrate admixed with eosinophils. Basal lymphoid aggregates may be present, as basal plasmocytosis which may be focal or diffuse. With active disease, one may see neutrophils in the lamina propria, cryptitis, multiple crypt abscesses, erosions, and granulation tissue. Paneth cell metaplasia may be present (Figs. 1 and 2). More than 80% of the patients with this pattern respond to medical or surgical treatment, although a few develop classical UC. Such a disease course is unlikely when the rectal mucosa is completely normal, although one should recall that rectal histology may normalize in UC patients treated topically with enemas or suppositories.

Diverticular Colitis, Fig. 1

Low power H&E stain shows colon mucosa with crypt distortion and an overall increased inflammatory infiltrate

Diverticular Colitis, Fig. 2

(Detail of Fig. 1). Basal lymphoid aggregates, dense mixed inflammatory infiltrate with cryptitis. These changes were limited to the mucosa of a diverticular sigmoid and descending colon. The patient has not developed ulcerative colitis over a follow-up period of 4 years

In the second form, mucosal disease is more patchy with an irregularly distributed architectural distortion and a variably dense inflammatory cell infiltrate. Granulomas, both due to crypt rupture or classical epithelioid forms, may be present (Figs. 3 and 4). This may cause confusion with Crohn’s disease, a problem which may be aggravated in colectomy specimens as other hallmarks of CD (such as thin deep ulcers, transmural lymphoid aggregates, serositis and creeping fat, and mural or lymph node granulomas) can then also be observed. The pathologist should be reluctant to offer a diagnosis of CD when these changes are limited to a diverticular sigmoid in an elderly person. In fact, the only strong argument for CD in such cases is the presence of histologically documented classical lesions elsewhere in the gastrointestinal tract.

Diverticular Colitis, Fig. 3

Low power H&E. Colon mucosa. Irregularly distributed crypt distortion and patchy infiltrate

Diverticular Colitis, Fig. 4

(Detail of Fig. 3). Presence of giant cells and an epithelioid granuloma. The changes were limited to a diverticular sigmoid. The patient had no changes suggestive of Crohn’s disease elsewhere at the time of biopsy 3 years ago, and has not developed them since

Immunophenotype, Molecular Features

These techniques are not used for diagnosis or stratification.

Differential Diagnosis

As indicated above, a small subset of patients with diverticular colitis, when followed endoscopically over time, evolves into a picture typical for ulcerative proctosigmoiditis or Crohn’s colitis. Therefore, a patient with presumed diverticular colitis should be re-evaluated clinically and endoscopically when symptoms persist or are progressive.