Case Series of Abdominal Actinomycosis: An Old Diagnostic Conundrum

Abdominal actinomycosis is a rare disease caused by the Actinomyces bacteria. We report a case series of two similar cases with a mismatch between the initial differential diagnosis, the radiological findings, the surgical findings, and the actual histological result. The first case is a 25-year-old woman with a month's history of right-sided abdominal pain. The diagnostic workup including computed tomography (CT) showed possible acute appendicitis, in addition to ascending colon looking abnormal with inflammatory changes and adjacent peritoneal nodules. A diagnostic laparoscopy revealed a normal-looking appendix and a hard mass involving the ascending colon potentially of inflammatory or malignant origin. A laparoscopic right hemicolectomy was performed. Surprisingly, the histology concluded actinomycosis. The second case is a 38-year-old woman with a six-week history of lower abdominal pain and right iliac fossa (RIF) swelling. The diagnostic workup including a CT scan showed a complex mass suggesting complicated appendicitis, pelvic inflammatory disease, or neoplastic process. Furthermore, magnetic resonance imaging (MRI) of the pelvis showed complex bilateral cystic lesions in both iliac fossas with an abscess formation within the subcutaneous fat overlying the lower pelvis. The patient underwent an ultrasound (US)-guided drainage of the subcutaneous pelvic collection and a diagnostic laparoscopy that showed an inflamed mass with dense adhesions to the anterior abdominal wall. Intraoperative biopsies were taken to confirm the diagnosis, which ultimately confirmed severe pelvic actinomycosis. Both patients were discharged home and received extended antibiotic treatment according to microbiology guidelines with good outcomes. Both cases are interesting because there was a mismatch between the initial differential diagnosis, the radiological findings, the intraoperative findings, and the final histology. Reported cases in the literature highlight the diagnostic challenges of abdominal actinomycosis, as it often presents with atypical symptoms and imaging findings sometimes mimic malignancy leading to surgical intervention.