Colonic Actinomycosis Presenting One Year After Partial Sigmoid Colectomy

Actinomycetes are commensal inhabitants of the oral cavity and gastrointestinal tract that can acquire pathogenicity through invasion of injured mucosa. Appendix and ileocecal regions are the most common sites involved in abdominal actinomycosis. We report a case of unusual site actinomycosis, in the rectosigmoid colon, presenting with abdominal pain and diarrhea after one year of partial sigmoid colectomy. A colonoscopy was done, which showed a 21 mm polypoid partially obstructing mass in the recto-sigmoid colon. Histopathology showed granulation tissue with severe acute inflammation, fibrinopurulent debris with areas of abscess, and branching filamentous organisms with sulfur granules consistent with actinomycosis. Abdominal actinomycosis can infect almost all organs within the abdominal cavity; however, it is more common around the ileocecal region.