Background: Colonic actinomycosis is an uncommon chronic infection associated with granulomatous inflammation resulting multiple abscesses and sinuses. Common modes of presentation include weight loss, malaise, abdominal pain, and abdominal mass, which might mimic neoplasia.

Methods: A 60-year-old female presented with painful lump in right iliac fossa (RIF) for 3 weeks and acute complete bowel obstruction for 3 days. Examination revealed hard, irregular and fixed lump in the RIF. Ultrasonography of abdomen and pelvis showed ileocecal mass while contract enhanced computed tomography (CECT) suggested carcinoma transverse colon with mesenteric metastasis. The patient underwent emergency exploratory laparotomy and right extended hemicolectomy for densely adherent mass incorporating distal ileum, cecum, ascending and proximal transverse colon with adjacent mesenteries. However, histopathological examination revealed colonic actinomycosis. The patient was commenced on intravenous penicillin G followed by oral amoxicillin. Colonic actinomycosis is a rare infection presenting with pain abdomen, change in bowel habit, and rarely, abdominal mass. Preoperative diagnosis is difficult due to lack of pathognomonic clinical, laboratory and radiological findings. Differentiation from other diseases such as appendicitis, diverticulitis, colon carcinoma, Crohn's disease, and ulcerative colitis is challenging. Diagnosis is confirmed histologically by presence of Periodic acid-Schiff (PAS) and Grocott- positive sulphur granules with filaments. Newer molecular diagnoses are under study. Medical therapy is main line of treatment, most effectively with parenteral and oral beta lactams.

Conclusions: Actinomycosis may present with aggressive invasion and infiltration of adjacent organs, mesentery, and abdominal wall mimicking malignancy. Acute presentation with bowel obstruction would mandate surgical intervention.