Pulmonary actinomycosis mimicking lung cancer on positron emission tomography

Pulmonary actinomycosis frequently mimics lung malignancy on radiologic imaging studies. Positron emission tomography-computed tomography (PET-CT) is a useful diagnostic modality for differentiating lung malignancy from benign diseases. However, few studies evaluated PET-CT findings of pulmonary actinomycosis. Therefore, it is unclear whether PET-CT is helpful to distinguish lung malignancy from benign lung disease when pulmonary actinomycosis is clinically suspected. We investigated PET-CT findings in 11 patients with pathologically confirmed pulmonary actinomycosis. The median maximal standardized uptake value (SUV) on PET-CT of pulmonary actinomycosis was increased to 5.5 (interquartile range, 4.2-8.8), which was higher than the threshold value of 2.5 indicating malignancy. Pulmonary actinomycosis without central necrosis demonstrated higher maximal SUV of 7.5 (4.9-12.2) compared to 4.8 (3.2-5.6) of ones with central necrosis. PET-CT might be not helpful in differentiating lung malignancy from benign lesions when pulmonary actinomycosis is clinically suspected.