Identification of submucosal eosinophilia in colonic diverticular disease

Aims: The etiopathogenesis of colonic diverticular disease remains unclear. Resident tissue eosinophils outside the mucosa are considered abnormal. We previously reported tissue eosinophilia in the mucosal base of colonic diverticula. This study aimed to quantify eosinophils and other immune cells, hypothesizing that tissue eosinophilia extends to the submucosa and adipose tissues in colonic diverticular disease. Methods: Hematoxylin and eosin-stained descending colon resections (n = 82, median age 71.5 [23–95], 42 M/40 F) containing diverticula were examined. Eosinophils, neutrophils, and lymphocytes in five high power fields in the submucosa and adipose were counted at the base, neck, and ostia of the diverticulum and compared to non-diverticula descending colon controls (n = 10, median age 68.5 [48–83], 5 M/5 F). The cohort was split into elective (n = 37, median age 72 [37–91], 19 M/18 F) and emergency (n = 45, median age 69 [23–95], 23 M/22 F) surgery cohorts. Results: Compared to controls (median 3.5 [95% CI 1.9–8.9]), eosinophil cell counts were modestly higher in the diverticula submucosal base of the emergency cohort (median 12 [95% CI 7–18], p = 0.01). Compared to controls (median 21 [95% CI 1.3–56]), lymphocyte cell numbers were higher in adipose tissue at the diverticulum base in both elective (median 56 [95% CI 21–55], p = 0.02) and emergency cases (median 66 [95% CI 51–88], p = 0.007). Conclusions: This is the first study to report submucosal elevated eosinophil cell counts at the base of the colonic diverticulum. This study suggests that, along with mucosal eosinophilia, increased submucosal eosinophils and adipose lymphocytosis may play a role in colonic diverticular disease pathophysiology.