ABSTRACT
Computed tomography of a Japanese man in his mid-forties with a complaint of right-side chest pain showed a dome-shaped smooth-surfaced mediastinal mass, which was extirpated. The cut surface was highly hemorrhagic and necrotic and not related to the original pulmonary tissues. Although routine sectioning detected bronchial cartilage, immunohistochemical analyses clearly showed the presence of alveolar type II cells; only the alveolar type II cells located at the periphery of this mass showed positive staining for cytokeratins, thyroid transcription factor 1, surfactant protein A, epithelial membrane antigen and Krebs von den Lungen-6. Thus, these analyses are useful for the detection of pulmonary components, even in severely hemorrhagic and necrotic tissues with marked sequestration. The clinical diagnosis was a rare, adult type of extralobar pulmonary sequestration accompanied by chest pain.