Hemangiopericytoma

     Hemangiopericytoma is a malignant vascular tumor that rarely occurs as a primary intraosseous lesion. The tumor is found most often in the pelvis, proximal femur, vertebrae and humerus but can occur anywhere. Hemangiopericytomas occur most commonly during the fourth and fifth decade but
affect patients age 12 to 90.
     Clinically, hemangiopericytomas may present with pain or a mass. The lesions grow slowly so it may be twenty years before a diagnosis is made.
     Hemangiopericytomas have almost no distinguishing characteristics radiologically. They may be lytic or cause focal sclerosis or they may have a honeycomb or reticular pattern.. They may cause cortical erosion which suggests the presence of a malignancy. CT scan and MRI are not helpful in
suggesting a diagnosis but they can help distinguish between benign and malignant lesions and help define the extent of the tumor. Angiography shows spider-like radial branching vessels.
     On gross examination, hemangiopericytomas may be well circumscribed and appear grayish white. The appearance is much less hemorrhagic than endothelial tumors. The consistency, like the radiology, is variable and may be solid or spongy, friable or granular.
     Hemangiopericytoma is a tumor thought to be derived from pericytes. The tumor cells are basophilic spindle shaped mononuclear cells that look like smooth muscle cells. The nuclei are round to oval and homogeneous. The cells have indistinct cytoplasmic borders. The tumor cells do not arise from endothelial cells even though they surround irregular vascular spaces. The branching vascular channels of varying sizes is often described as a "staghorn" pattern. Silver stain highlights the reticulin sheath that surrounds each cell and confirms that the tumor cells are outside the vascular spaces. The fact that the tumors cells do not stain positive for actin suggests that they may have another cell of origin than pericytes.
     Treatment for primary hemangiopericytoma of bone depends on the grade. Wide surgical resection is performed if possible. The role of chemotherapy and radiation is uncertain at this time, but they may be helpful in high grade or difficult to reach lesions. The higher grade lesions do metastasize to lung. There is a 5 year survival of 75%¹ but the long term prognosis is often fair to poor.

References
^lTang, JSH et al., Hemangiopericytoma of Bone, Cancer, 62:848-859, August 15, 1988.

Nappi, O. et al, Hemangiopericytoma:Histopatholgical Pattern or Clinicopathologic Entity?, Seminars in Diagnostic Pathologv, 12(3):221-232,August, 1993.

Bullough, Peter, Orthopaedic Pathologv (third edition), Times Mirror International Publishers Limited, London, 1997.

Huvos, Andrew, Bone Tumors:Diagnosis. Treatment and Prognosis, W.B.
Saunders, Co., 1991.

Fletcher, Christopher, Diagnostic Histopathologv of Tumors, Churchill Livingstone, 1995.