summary Hemangioendothelioma, also known as hemangiosarcoma, is a rare, malignant, vascular tumor with endothelial differentiation that is more common in soft tissues than bone. The tumor typically presents in patients between ages 30 and 40 with regional pain. Diagnosis is made with biopsy and histology showing angiocentric growth expanding the vessel wall with surrounding sclerosis. Treatment is usually radiotherapy alone for low-grade lesions. Surgical resection with or without radiation is indicated for high-grade lesions. Epidemiology Demographics occurs most commonly in 4th - 5th decade women affected more than men Anatomic location more commonly in soft-tissue > bone usually occurs in the lower extremity Risk factors exposure to arsenic Etiology Pathophysiology pathoanatomy arise from the lining of blood vessels cellular biology distinct histologically and molecularly from benign hemangioma and high-grade angiosarcoma stratified into two groups based on size of tumor and mitotic activity classic malignant Presentation Symptoms local pain not usually associated with swelling Imaging Radiographs recommended views 2 or 3 views of affected bone findings lytic lesion with no reactive bone areas of cortical destruction and cortical expansion are common CT indication cross-sectional imaging to better define the area of concern findings multifocal eccentric lytic lesions in bone matrix mineralization may be present calcification and periosteal reaction is rare MRI indication cross-sectional imaging to better define the area of concern findings high signal intensity on T2-weighted images edematous bone reaction surrounding the lesion Histology Macroscopic angiocentric growth expanding the vessel wall obliterating the lumen and spreading centrifugally into surrounding tissue induce a sclerotic response Microscopic arranged in single files, cords and small nests typically lack well-formed vascular channels, with only immature, intracytoplasmic lumina Differential Langerhans cell histiocytosis (LCH), angiosarcoma, infection, myeloma, metastasis, and lymphoma the diagnosis of hemangioednthelioma requires histopathologic analysis Treatment Nonoperative radiation therapy alone indications low grade lesion (classic) chemotherapy the role of chemotherapy is not yet clear Operative surgical resection +/- radiotherapy indications high grade lesion (malignant) Prognosis Natural history of disease malignant tumor > 3cm and >3 mitoses/50 HPFs have 5 year survival of 59% classic 100% survival if lack these features Prognostic features 20 - 30% of tumors metastasize visceral involvement is considered the most important criterion in predicting survival