[Pulmonary actinomycosis mimicking of mucosa-associated lymphoid tissue lymphoma by frozen section examination: report of a case].

A 59-year-old man was admitted to our hospital for hemoptysis. Chest X-ray films showed a mass shadow in the left lower lobe. Any definitive diagnosis could not be made after examinations including sputum culture and bronchial cytology. Exploratory thoracotomy was performed since malignancy was not excluded. During the operation, mucosa-associated lymphoid tissue (MALT) lymphoma was suspected based on the pathological findings of the frozen section. The permanent section of the resected specimen contained colonies of actinomycetes in the bronchus, and the peripheral region demonstrated marked infiltration of lymphocytes and plasma cells through the interstitium of alveolar walls and peri-bronchovascular sheath, with many lymphoid follicles. This case revealed pulmonary actinomycosis coexisted with lymphocytic interstitial pneumonia (LIP). We concluded that lymphoproliferative disease should be considered another candidate for the differential diagnosis from pulmonary actinomycosis.