Pelvic actinomycosis masquerading as sigmoid cancer: an unusual cause of closed-loop small bowel obstruction

Actinomycosis is a rare chronic bacterial infection, with pelvic involvement accounting for ~5% of cases. Surgery may be required if there is intestinal obstruction, abscess formation, severe infection, or if malignancy cannot be excluded. We report a 46-year-old woman with a 12-year history of an intrauterine device, presenting with abdominal pain, vomiting, constipation, lethargy, and malaise. Examination revealed abdominal distension, tenderness, and a left iliac fossa mass. Computed tomography imaging showed a complex, infiltrative pelvic mass involving the sigmoid colon and adjacent structures, including the small bowel, causing a closed-loop small bowel obstruction and raising suspicion of malignancy. She underwent emergency laparotomy with small bowel resection and anastomosis, Hartmann's procedure, and bilateral ureteric stent insertion. Histology confirmed actinomycosis. She recovered well and commenced a 1-year antibiotic course. Pelvic actinomycosis demands a multidisciplinary approach with combined surgical and medical management due to its complex presentation and tendency to mimic other conditions.