Sigmoid colon pseudotumor of actinomycosis: a rare case

Actinomycosis is a chronic suppurative infection caused by gram-positive bacteria, Actinomyces, which commonly colonize the oral cavity, urogenital tract and gastrointestinal tract. It causes opportunistic infection where the mucosal barrier is compromised and is often misdiagnosed as malignancy. We report a case of a 58-year-old female with severe abdominal pain and a palpable tender mass in the left lower quadrant. Computed tomography scan with contrast showed thickening of the transverse, descending to sigmoid colon wall and intense contrast enhancement resembling colitis with mesenteritis. At laparotomy, we found an adherent mass involving sigmoid colon with adjacent small bowel and peritoneum. We decided to perform adhesiolysis and Hartmann procedure. The culture result was negative, whereas the biopsy of sigmoid colon revealed characteristic sulfur granules of actinomycosis colony. Intravenous antibiotic combination of ceftazidime and metronidazole was administered for 14 days followed by complete resolution of symptoms. Histopathological and bacteriological examinations are keys to diagnose actinomycosis. Patients require long-term antibiotic therapy, but surgery is often required because preoperative diagnosis is difficult.