Telangiectatic osteosarcoma is a subtype of osteosarcoma; it constitutes 2.5%-12% of all osteosarcoma and has poorer prognosis than those with conventional osteosarcoma and aggressive growth features.

It is believed to originate from transformed osteoblasts that derive from mesenchymal tissue. The majority of the tumor volume (90% or more) consists of large hemorrhagic or necrotic cavities, which can mimic an aneurysmal bone cyst.

The clinical manifestations of telangiectatic osteosarcoma resemble those of conventional osteosarcoma. Patients mostly present with pain, a soft tissue mass, and fracture.

Telangiectatic osteosarcoma is usually osseous in origin and occurs in the medullary cavity in the metaphyseal region of the long bones. The most frequent site is the distal femur (45%).

The radiographic appearance is a lesion with geographic bone destruction, a wide zone of transition, and endosteal scalloping. Expansile bone remodeling is common and the osteoid matrix is subtle because most of the lesion is necrotic.

The distinction between telangiectatic osteosarcoma and aneurysmal bone cyst is usually made with MR imaging. An aneurysmal bone cyst has limited thin peripheral septa (usually 2-3 mm thick), which are often best seen as enhancing structures that lack nodularity on gadolinium-enhanced images. Conversely, in telangiectatic osteosarcoma, the periphery and septa around the hemorrahagic spaces are thickened and often nodular and enhance with gadolinium.