Object: The purpose of this study was to compare histopathological changes with imaging findings in different tumors after gamma knife radiosurgery (GKS).
Methods: Five patients of a series of 220 treated with GKS underwent craniotomy for tumor removal 3 to 12 months after radiosurgery. There were two patients with multiple cerebral metastases, one with vestibular schwannoma, one with malignant glioma, and one with meningioma. A portion of normal brain tissue outside the prescription dose volume was acquired wherever possible to facilitate examination of the effects of radiosurgery. Histopathological and immunohistochemical investigations were performed. In addition to the routine hematoxylin and eosin and Mallory trichrome stains, immunohistochemical reactions were also performed for Factor VIII-associated antigen (FVIII) and CD34 antigen to study vascular endothelial effects of the irradiation. Endothelial cells of vessels in the normal brain tissue covering the tumor, outside of the prescription isodose volume, expressed marked CD34 and FVIII positivity. In the irradiated targeted tumor tissue samples, however, both reactions decreased remarkably.
Conclusions: The results of the present immunohistochemical study provide support to the experimental hypothesis that vascular endothelial cells are the principal targets of single high-dose irradiation. The loss of central contrast enhancement of tumor tissue following radiosurgery might be consequence of the vascular damage.