Osteosarcoma is the most common primary malignant bone tumor in children and adolescents. When first recognized, telangiectatic osteosarcoma was proposed to be a distinct clinical and pathologic entity.  On the basis of subsequent findings that provided a better understanding of the condition's presentation and prognostic implications, telangiectatic osteosarcoma should be considered a variant of osteosarcoma. It is an uncommon variant, accounting for 0.4-12% of all osteosarcomas. [2, 3, 4, 5, 6]
Telangiectatic osteosarcoma appears as a painful, radiographically lytic mass lesion in the metaphyseal portion of the long bones. It is characterized by dilated, blood-filled vascular spaces lined by malignant osteoblasts. These osteoblasts are separated by fibrous septa, which contain the malignant cells, multinucleated giant cells, and tumor osteoid. 
Because of the rarity of this lesion, the etiologic factors that promote malignant transformation have not been extensively investigated. Telangiectatic osteosarcomas are presumed to originate from transformed osteoblasts or from stem cells that are of mesenchymal derivation.
Results from transmission electron microscopic examination show that in addition to undifferentiated osteoblastlike and fibroblastlike tumor cells, angiosarcomatous elements may be observed in this malignant bone tumor. Endothelial cell–like structures, including pinocytotic vesicles, tight intercellular junctions, fine fibrils, and Weibel-Palade bodies, are seen in the cytoplasm of these cells.  Such observations suggest that telangiectatic osteosarcoma may be derived from multipotential mesenchymal cells, with possible differentiation along various pathways. 
Familial occurrence has been reported at least once.  In all cases of telangiectatic osteosarcoma, familial genetic changes may be responsible, but other causes are more likely. Molecular and cytogenetic studies are necessary to resolve these issues. 
Telangiectatic osteosarcoma occurs in a male-to-female ratio of 2:1. Although disease can be found in patients as young as 3 years and as old as 71 years, it rarely occurs in persons older than 25 years. Most patients present between the ages of 10 and 20 years. 
Historically, local recurrence has been found to be more common than metastasis. [13, 14, 5, 15] With the use of preoperative chemotherapy, however, this observation is probably less accurate than it was. Telangiectatic osteosarcomas have vascular spread and therefore, similar to conventional osteosarcomas, metastasize to the bones and lungs. [13, 14]