[A case of pulmonary actinomycosis marked by diagnostic difficulty].

A 59-year-old man was admitted to our hospital for evaluation of an abnormal lung shadow. Chest X-ray and computed tomographic (CT) films showed a mass shadow in the left lower lobe. The shadow decreased in size after the administration of imipenem/cirastatin and clindamycine. Although a transbronchial lung biopsy failed to confirm the diagnosis, histologic examination of percutaneous aspiration biopsy specimens revealed sulfur granules. Actinomycosis was diagnosed but we did not rule out the possibility of coexistent carcinoma. A left lower lobectomy was performed, and the patient has been well without any complaints or recurrence of actinomycosis for 6 months after surgery. We concluded that pulmonary actinomycosis should be considered another candidate for the differential diagnosis of mass shadows from lung cancer.