Although this tumor is also known as a hemangiosarcoma, hemangioendothelial sarcoma, and malignant hemangioendothelioma, these secondary terms should be avoided to prevent confusion with epithelioid hemangioendothelioma, which is a separate entity.
Angiosarcomas of bone are very rare and account for less than 1% of all angiosarcomas in any organ and less than 1% of primary bone tumors. [1, 2] Although patients with these tumors range in age from 12 to 74 years, most patients are in their 30s or older; angiosarcomas are generally rare before then.  Males are more commonly affected than females in a ratio of approximately 2 to 1.
En bloc excision or amputation is the therapy of choice for angiosarcomas.  Curettage is inevitably followed by local recurrence, [4, 5] and metastases are common.  The effects of radiation therapy and chemotherapy have not been adequately assessed. 
Go to Angiosarcoma for complete information on this topic.
Clinical Features and Imaging
Pain is the usual presenting symptom.
Angiosarcomas produce lytic lesions with ill-defined borders and destructive patterns on radiologic studies (see the following image). [2, 3, 6] The femur, tibia, and humerus are about equally affected and account for approximately 50% of angiosarcoma cases.  The vertebrae, pelvic bones, and ribs are less commonly affected sites, but virtually every bone has been reported with these lesions. [2, 2, 5]
The cortex is often eroded with extension into the soft tissues. Although most of these tumors are solitary, multifocal lesions can be seen. Computed tomography (CT) scans can often help in determining intralesional mineralization and the invasive nature of this sarcoma.  Magnetic resonance imaging (MRI) findings are relatively nonspecific, with low signal on T1 and high signal on T2 sequences, as seen in the images below. [1, 3]
Gross, Microscopic, and Immunohistochemical Features
The gross appearance of angiosarcoma is that of soft, dark red tissue that may have a spongy consistency (see the image below).  Solid gray areas may be interspersed with embedded bone fragments if the cortex has been breached.
On histologic sections, the diagnosis of angiosarcoma is made in areas of well-formed, anastomosing vascular channels  lined by enlarged endothelial cells with hyperchromatic or vesicular nuclei (see the first image below).  These endothelial cells have a large nuclear-to-cytoplasmic ratio. Although these features are readily identifiable, most skeletal angiosarcomas have poorly differentiated areas without regular vascular channels and can be very difficult to identify. [2, 4, 3] The tumor cells in these areas may be closely packed, round, ovoid, or spindle cells that resemble undifferentiated sarcoma (see the second image below). 
Immunohistochemistry is often necessary to reach a diagnosis of angiosarcoma, given the anaplasia in most of the tumors. Immunohistochemistry for vimentin, CD31, CD34, and focally for von Willebrand factor are usually positive in these tumors (see the image below). [2, 4, 7]