Solitary Pulmonary Nodule Due to Mycobacterium kansasii

A 46-year-old man with no past history of underlying disease was admitted to our hospital for examination of abnormal chest shadow on chest radiograph. He had no respiratory symptoms on admission. Chest radiograph showed a solitary nodule (35x20 mm) in the left upper lung field. On chest CT, this nodule in the left upper lobe (S1+2) did not demonstrate calcification, the margin was clear but irregular, and there was pleural indentation. The solitary nodule was strongly positive on PET/CT. Therefore, we suspected primary lung cancer. Because we could not establish the diagnosis by bronchoscopic examination, video-assisted thoracoscopic surgery (VATS) was performed. Histological diagnosis of the solitary nodule demonstrated epitheloid granuloma with caseous necrosis. Smear test of the resected tissue was positive for acid-fast bacilli and culture was positive for mycobacteria, which was identified as Mycobacterium kansasii. There are a few case reports of solitary nodule due to M. kansasii.