Symplastic hemangioma: report of two cases.

Symplastic hemangioma is characterized by degenerative atypia of vascular smooth muscle and interstitial cells within a pre-existing vascular lesion with minimal endothelial cell atypia. We describe an additional two cases of this distinctive but poorly recognized entity. On histology, both lesions revealed a cirsoid aneurysm-type appearance with thick-walled and variably dilated blood vessels. The vascular endothelial cells showed mild nuclear hyperchromasia with no multilayering or mitoses. The atypical cells, either located within the vascular smooth muscle wall or within the interstitium, were spindle or epithelioid with varying degrees of hyperchromasia, nuclear enlargement, pleomorphism, and multinucleation. Perivascular hemorrhage, vascular thrombosis, and focal papillary endothelial hyperplasia were uniformly present. The variably fibrous to edematous stroma showed hemosiderin deposits and a mononuclear inflammatory infiltrate. Clusters of adipocytes were present within the superficial dermis. Rare atypical mitoses and occasional bizarre lipoblast-like stromal cells were identified in one tumor. Immunohistochemistry showed focal smooth muscle actin positivity in the pleomorphic cells of the vascular walls. CD68 and CD34 stained occasional stromal cells in the interstitial location. Both the cases showed no recurrence. The bizarre cytologic changes are interpreted as degenerative in nature and probably akin to that observed in ancient schwannoma and uterine symplastic leiomyoma.