The biologic behavior of an hemangiopericytoma can be difficult to predict but there are certain pathologic features associated with a malignant course.
The presence of metastases at the time of diagnosis indicates malignant behavior.
Pathologic features associated with rapid growth, recurrence and/or or metastasis for hemangiopericytomas:
(1) size > 5 cm
(2) mitotic rate
(3) foci of necrosis
(4) hypercellularity
(5) foci of hemorrhage
(6) any degree of cellular pleomorphism
Mitotic Rate per 10 High Power Fields
Diagnosis
>= 4
malignant
3
borderline
0 - 2
benign
The 2 most important criteria for distinguishing benign from malignant hemangiopericytomas are:
(1) mitotic rate
(2) foci of necrosis
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