Fig. 3

Microscopic and immunohistochemical findings of the resected specimen. a Hematoxylin-eosin staining (low power field). The inside of a well-demarcated nodule consisted of the dilated vascular lumen with vascular endothelial cells and smooth muscle components. The vascular endothelial cells were histological findings of cavernous hemangioma, and no malignant features were observed. Although the smooth muscle proliferated, it did not surround the lumen of the vessel and was considered unlikely to be neoplastic. b–f Immunohistochemical staining (low power field) showed CD31- (b), CD34- (c), and von Willebrand factor (vVF)-positive endothelial cells (d) in the vascular lumen and α-smooth muscle actin-positive cells in the smooth muscle component (e). Elastic van Gieson (EVG) staining (f) showed irregular elastic fibers, and the distribution of elastic fibers was continuous in the surrounding lung tissue and hemangioma tissue, indicating that the smooth muscle cells did not form a neoplastic vessel wall. Based on the above findings, the lesion was considered to be pulmonary cavernous hemangioma complicated by smooth muscle hyperplasia