Case of solitary pulmonary capillary hemangioma: pathological features based on frozen section analysis.

Solitary pulmonary capillary hemangioma (SPCH) is a rare benign lung tumor that must be distinguished from small and early lung cancers. Here, we report a case of SPCH for which we performed frozen section diagnosis. The patient was a 55-year-old Japanese woman. Five years before the operation, mixed ground-glass opacity was detected by computed tomography in the left posterior basal segment of the lower lobe (S10). Because the interior tumor density of the ground-glass opacity increased slightly, video-assisted thoracic surgery wedge resection was performed. Frozen section diagnosis revealed a benign tumor without proliferation of atypical epithelial cells. The tumor had narrow alveolar lumens, thickened alveolar septa and a clear boundary separating it from normal lung tissue. The proliferated lumens varied in size and were lined with single layers of flat cells. After the operation, immunohistochemical staining of a paraffin section revealed that the thickened alveolar septa resulted from the proliferation of capillary vessels, the flat cells of which were positive for CD31 and CD34 and negative for podoplanin; the tumor was diagnosed as SPCH. Here, we discuss the pathological features of SPCH on frozen sections with reference to this case and review previous related reports.