A case of solitary fibrous tumor of the pleura

Background: Solitary fibrous tumor originating in the pleura is relatively rare. Cytological differential diagnosis of spindle cell tumors is discussed. Case: The patient was a 47-year-old female who was checked for abnormal thickening of the pleura. Because of increasing size of the mass, she was admitted to our hospital. Mesothelioma was suspected by ultrasonography and CT. As malignancy could not be completely denied, the tumor was surgically resected. Intraoperative cytology revealed cohesive spindle cells with scant cytoplasm arranged in fascicular pattern. Nuclear anisokaryosis and irregularity were mild, and chromatin pattern was fine granular. Increased mitotic figures or necrosis were not observed. Histologically, spindle-shaped tumor cells proliferated in a fascicular pattern with abundant collagen. Immunohistochemically, tumor cells were positive for vimentin and CD 34, and partially positive for smooth muscle actin. Conclusion: Low cellularity, arrangement in fascicular pattern, naked tumor cells, mild nuclear atypia, and no mitotic figures were useful cytological findings to exclude other spindle cell tumors arising in the pleura.