RESUMO
Inflammatory pseudotumor of the lung is considered to be a rare, benign, neoplastic lesion, consisting mainly of spindle mesenchymal cells, sometimes in such a way that its histological appearance mimics that of a spindle cell sarcoma, fibrous histiocytoma or fibrosarcoma. A case of inflammatory pseudotumor of the lung occurring in a 13-year-old boy is reported with pathologic findings, including its ultrastructure. The patient had had no symptoms and accidentally discovered his condition after a chest X-ray examination at a regular school physical check up. The mass was located in the suprahilar area of the left lung. Exploratory thoracotomy revealed a large mass that was removed, together with the left upper lobe of the lung. Microscopically, the mass was composed of numerous interstitial inflammatory cells, mainly lymphoplasma cells. Ultrastructurally, the spindle-shaped mesenchymal cells were arranged haphazadly and the normal pulmonary structure was nearly totally destroyed. Emphasis is given to complete resection of the tumor for both diagnostic and therapeutic purposes.