Vertebral hemangiomas: common lesions with still many unknown aspects
Histologically VHs are not considered vascular neoplasms, but rather hamartomas or malformation of the microcirculation. Basing on the predominant type of vascular channel they are classified in: capillary, cavernous, arterio-venous and venous malformations. Most of spinal epidural hemangiomas belongs to the cavernous type (1). Numerous terms have been introduced and different classification systems. Unfortunately, none of these has been accepted due to the lack of accepted histological criteria and limited correlation with clinical outcome. Vascular tumours of bone originate from endothelial cells resulting in variable expression of endothelial markers, but none of these markers is useful to discriminate between benign and malignant lesions. Verbeke and Bovée (2) proposed the classification of vascular tumours of bone according to the WHO classification scheme for soft tissue tumours dividing entities into benign, intermediate and malignant category. Hemangioma is the most commonly recognized benign lesion. Epithelioid hemangioma was better defined over the past few years. Based on its locally aggressive behaviour and occurrence of lymph node metastases, its classification within the intermediate category could be considered. Angiosarcoma is the only accepted term for high-grade malignant vascular tumour of bone and epithelioid hemangioendothelioma is the only accepted low-grade malignant vascular tumour of bone. It is still unclear whether other low grade malignant vascular tumours of bone (e.g., hemangioendothelioma) truly exist. Molecular/genetic studies of vascular tumours of bone which might support the proposed classification are very sparse.