The family of epithelioid vascular tumors.

Vascular tumors characterized by proliferation of epithelioid (histiocytoid) endothelial cells with abundant eosinophilic hyaline cytoplasm span a broad spectrum of histologic appearances and behaviour. They can occur in a wide variety of sites, such as soft tissues, skin, bone and visceral organs. On the benign end are the epithelioid hemangiomas (angiolymphoid hyperplasia with eosinophilia), which are composed predominantly of well formed vascular channels, and are frequently accompanied by an infiltrate of lymphocytes and eosinophils. In the literature, they have often been confused with Kimura's disease, an idiopathic allergic-inflammatory condition. There have also been controversies as to whether these lesions are neoplastic or reactive. In the middle of the spectrum are the borderline or low grade malignant epithelioid hemangioendotheliomas, characterized by isolated, cords and nests of epithelioid endothelial cells disposed in a hyaline or myxoid matrix; cytoplasmic vacuoles are common. However, the morphologic variations on this theme are very wide rendering recognition of these tumors difficult sometimes. On the malignant end are highly aggressive epithelioid angiosarcomas showing predominantly solid growth and significant nuclear pleomorphism. In addition, there are also cases showing histologic features straddling the borderline areas between the above three defined categories. In this review, the broad morphologic appearances of these epithelioid vascular tumors are discussed and illustrated.