Actinomyces and Actinobacillus mixed infection with abdominal wall and intrathoracic pseudotumor

Abstract Actinomycosis is a rare pediatric infectious disease. In this paper, we describe a case of a healthy 13-year-old girl with Actinomyces and Actinobacillus mixed infection. She presented with a rapid-growing right abdominal mass 2 weeks prior to hospitalization. Computed tomography (CT) images showed multiple tumorlike lesions over the right upper abdominal wall, right lower lung, and right posterior chest wall. Further, the surgical biopsy of the abdominal mass revealed necrotic tissue with pus discharge. The Gram stain examination of pus showed numerous Gram-positive bacilli. The pus culture yielded not only Gram-negative bacilli (Actinobacillus) at first but also Actinomyces 2 weeks later. Furthermore, the histopathology of surgical tissue showed suppurative granulomatous inflammation with sulfur granule and filamentous bacteria suggestive of actinomycosis. The girl received parenteral ampicillin/sulbactam and ultrasound-guided percutaneous pigtail drainage catheter. Based on the normal findings of the immunological survey, dental examination, and transesophageal echocardiography, the girl was discharged on the 16th day of her hospitalization and prescribed oral amoxicillin/clavulanic acid treatment for 4 months. In this case, actinomycosis presented with multiple site masses mimicking malignancy but eventually turned out to be inflammatory pseudotumors. Besides, the patient also acquired coinfection with Actinobacillus without any preceding risk factors. In such case, tissue biopsy and culture are required for accurate diagnosis and pathogen identification.