Abdominopelvic Actinomycosis Mimicking Malignant Tumors: Two Case Reports

BACKGROUND: Abdominopelvic actinomycosis is a rare chronic suppurative granulomatous infection that often mimics malignant tumors on imaging, leading to preoperative misdiagnosis and unnecessary radical surgery. This report aims to highlight key clinical and imaging features that can aid in differentiating this entity from malignancy. METHODS: We retrospectively reviewed two cases of abdominopelvic actinomycosis confirmed by surgical pathology. Clinical presentations, laboratory findings, imaging characteristics (ultrasound, MRI, and CT), and pathological results were analyzed. RESULTS: Both patients presented with non-specific symptoms (abdominal dull pain/distension). Imaging revealed ill-defined, irregular heterogeneous masses with moderate-to-high resistance flow on ultrasound (RI 0.63-0.70) and no ascites. One case had a history of cesarean section; the other long-term intrauterine device (IUD) use (20 years). Preoperative imaging suggested malignancy, but postoperative pathology confirmed actinomycosis with inflammatory adhesions, microabscess formation, and reactive lymph nodes. Both patients underwent surgical resection with good outcomes and no recurrence during follow-up. CONCLUSION: Abdominopelvic actinomycosis should be considered in the differential diagnosis of pelvic masses, especially in women with IUD use or abdominal surgery history. Key differentiating features include moderate-to-high resistance flow, absence of ascites, internal cystic changes (microabscesses), and infiltrative changes due to adhesions rather than destructive invasion. In selected diagnostically challenging cases, preoperative core needle biopsy may help avoid unnecessary extensive surgery; however, surgery remains indicated when malignancy is strongly suspected or complications are present.