HEMANGIOMAS, LYMPHANGIOMAS, AND REACTIVE VASCULAR PROLIFERATIONS

Abstract

Benign vascular tumors and tumor-like conditions include a wide variety of clinicopathologic entities, among them different types of hemangiomas, vascular malformations, teleangiectasiae, hemangioma-like reactive vascular proliferations, and lymphangiomas. Also included in this discussion is kaposiform hemangioendothelioma, a hemangioma variant without metastatic potential (although one having potential for fatal complications through thrombocytopenia). The discussion of specific tumor entities is preceded by a synopsis of endothelia and angiogenesis given for biologic background information relevant for vascular tumors. The genetic background of inheritable hemangiomas and vascular malformations is becoming known from the hereditary syndromes, but the somatic genetics of hemangiomas is still poorly understood. Borderline (hemangioendotheliomas) and malignant vascular tumors (angiosarcoma) are discussed in Chapter 22. Hemangiopericytoma is considered related to solitary fibrous tumors, and these tumors are discussed together (Chapter 12). Vascular smooth muscle tumors, vascular leiomyoma and leiomyosarcoma, are discussed with other smooth muscle tumors (Chapter 16), and lymphangiomyoma is included among PEComas (Chapter 19). Glomus tumor and angiomyopericytoma have significant vascular components while also containing smooth muscle–related elements (Chapter 23). Biology of Endothelia and Angiogenesis Endothelial cells are mesenchymal cells that not only form a protective epithelial-like inner lining in the lumen of the blood vessels and lymphatics but also have several other vasoregulatory functions. These include regulation of vascular permeability and caliber, transport of metabolites (e.g., cholesterol), and regulation of leukocyte adhesion, trafficking, and hemostasis. External signals from growth factors/cytokines secreted by a variety of cells modulate the differentiation, antigen expression, and functional state of endothelial cells.