[Pulmonary actinomycosis that was difficult to make an accurate diagnosis].

A 35-year-old man was referred to our hospital, because of recurrent pneumonia. His chest X-ray film and computed tomography showed mass-like consolidation with a cavity in the right upper lobe. He underwent a bronchoscopic examination, but no diagnosis was established. Therefore a surgical biopsy was performed, but the pathological findings revealed that it was only an inflammatory change without any malignant component. For a while, antibiotic and the steroid treatment was continued resulting in the aggravation of clinical findings. Finally, an upper lobe excision was performed for the complete excision of the lesion. As a result of pathology, pulmonary actinomycosis was diagnosed.