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.
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