Primary pulmonary meningioma: A rare case report of aspiration cytological features and immunohistochemical assessment.

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Ectopic meningioma is a generally rare type of benign tumor that very rarely occurs in the lung. Here, we report the cytological findings of a primary pulmonary meningioma with a particular focus on immunohistochemical (IHC) assessment. A healthy 60‐year‐old woman visited our hospital with an asymptomatic nodule in the right lower lung lobe. She had no particular past‐history and no other tumors in the central nervous system or elsewhere according to an imaging examination. Transbronchial fine‐needle aspiration cytology revealed clusters of spindle cells in a whorled formation and psammoma bodies. The tumor cells exhibited spindle‐shaped cytoplasm, small fusiform or round nuclei and numerous intranuclear cytoplasmic inclusions. IHC staining of the cytological specimen revealed that the tumor cells were positive for epithelial membrane antigen, negative for thyroid transcription factor‐1 and p40, and equivocal for claudin‐1. Progesterone receptor immunoreactivity of cytology specimen resulted negative at first by manual method but retrieved positive by an autostainer. Following segmentectomy, the pathological diagnosis was a meningothelial meningioma. The patient has remained well without recurrence for 36 months postoperatively. Because the cytological preparation exhibited characteristic findings of meningioma, a correct diagnosis based on pre‐operative cytological findings with appropriate IHC would be possible. Here, we report the cytological and IHC features of this case and highlight the importance of IHC‐quality assurance.