[Pulmonary actinomycosis resembling an anterior mediastinal tumor].

A 25-year-old, previously healthy man was referred to us because of fever, left-sided chest pain, and an abnormal mass shadow at the left pulmonary hilum on chest X-ray films. Laboratory tests and fiberoptic bronchoscopy revealed no abnormality. Thoracotomy was done because a mediastinal tumor was suspected. Surgery revealed that the left lingula was atelectatic and that the mass was in the left S4, not in the mediastinum. Pathological examination of tissue from the partially resected lung showed sulfur granules, and a diagnosis of pulmonary actinomycosis was made. At least 80 cases of pulmonary actinomycosis were reported in Japan between 1963 and 1995. Pulmonary actinomycosis is most common among men in the fifth and sixth decades of life, and almost all patients have oral disease. Pulmonary actinomycosis is often difficult to distinguish from lung cancer, because both appear as mass shadows on X-ray films, and almost all cases of pulmonary actinomycosis are diagnosed by thoracotomy.