Pulmonary sclerosing hemangioma presenting with dense spindle stroma cells: a potential diagnostic pitfall

Pulmonary sclerosing hemangioma (PSH) is an uncommon pulmonary tumor. Histologically, PSH typically consists of two types of cells, surface cuboidal cells and polygonal cells, four architectural patterns including papillary, sclerotic, solid, and hemorrhagic. Herein, we present a case of PSH in a 59-year-old Chinese female. The tumor was predominantly composed of solid area presenting with diffuse spindle cells rather than polygonal cells. Focally, classical papillary and sclerotic area could be seen. Immunohistochemical staining showed that the spindle cells were positive for TTF-1, EMA, Actin(SM) and Vimentin, and negative for cytokeratin, cytokeratin7, cytokeratin5/6, surfactant apoprotein A, surfactant apoprotein B, CD34, CD99, S-100, HMB45, Desmin, Synaptophysin, CD56, ALK and Calretinin. The immunophenotype of the dense spindle cells in this case was similar to that of the polygonal cells, and thus the spindle cells may be the variants of polygonal cells. Based on morphologic features and the immunohistochemical profile, the tumor was diagnosed as a PSH. The significance of spindle cells change is unclear for us. To our knowledge, this is the first reported case of PSH showing dense spindle cells in solid area. This case represents a potential diagnostic pitfall, as it may be misdiagnosed as a mesenchymal tumor such as inflammatory myofibroblastic tumor, synovial sarcoma, solitary fibrous tumor, leiomyoma, or even mesothelioma, especially if the specimen is limited or from fine- needle aspiration.