Actinomycosis of the Sigmoid Colon Mimicking Malignancy and Presented with Bowel Obstruction

<b><i>Background:</i></b> Actinomycosis is a chronic inflammatory condition caused by <i>Actinomyces israelii</i> or other <i>Actinomycetes</i> species, with primary abdominopelvic involvement being the most important form of the disease, especially when there is splanchnic infiltration. In cases of colonic involvement, the disease is often misdiagnosed as a neoplasm by imaging studies, and surgery is undertaken. <b><i>Case Presentation:</i></b> We report the case of a 48-year-old male living in a rural area in whom a computed tomography (CT) scan showed a large, irregular abdominopelvic mass infiltrating the urinary bladder, the left ureter, and the sigmoid colon with luminal obstruction. He was referred with the presumptive diagnosis of abdominal sarcoma for surgical evaluation and treatment. He underwent a Hartmann's procedure with resection of the sigmoid colon and formation of an end colostomy. Multiple tissue samples were taken from the mass for histopathological examination. The correct diagnosis was made after pathological examination by detection of actinomycetes colonies. Penicillin-based therapy was commenced and continued for six months, when a CT revealed complete resolution of the pre-operative findings without any evidence of a mass. <b><i>Conclusion:</i></b> Although rare, actinomycosis should be considered in the differential diagnosis of colonic neoplastic lesions. Proper long-term antibiotic treatment is necessary for complete eradication of the infection and resolution of tissue alterations.