Morphological observations in brain arteriovenous malformations after gamma knife radiosurgery.

Morphological studies after Gamma Knife radiosurgery (GKRS) revealed endothelial destruction followed by spindle-shaped cell proliferation in the subendothelial region and in the connective tissue stroma of arteriovenous malformation (AVM) vessels. Histological, immunohistochemical and ultrastructural characteristics of this spindle-shaped cell population in the irradiated AVMs were reminiscent of those described as myofibroblasts in wound healing processes and pathological fibromatoses. These modified fibroblasts have contractile capacity, therefore this might contribute to the vessel occlusion, shrinking process and final volume reduction of AVMs after GKRS. Similar histopathological changes were observed in a cavernous malformation following high-dose irradiation.