Fig. 1

Axial contrast-enhanced MRI brain images showing a small delayed radiation necrosis in the area of a metastatic brain tumor treated by SRS (a) at initiation of T-DM1 (15 mm), (b) heterogeneous enhancement (42 mm) at 14 months and (c) rapid progression of nodular lesion (58 mm) at 15 months after initiation of T-DM1. Precontrast CT scan shows heterogeneous high density area in this lesion (d). The lesion is shown as an area of low cerebral blood volume (CBV) by perfusion CT (e). Photomicrographs of the removed lesion on Hematoxylin and Eosin (H-E) (f), CD31 (g) and Elastica van Gieson (EVG) (h) immunohistochemical stains. The scale bar represents 500 μm for panel. Hemorrhage and dilated vessels are shown (f). The area surrounded by white square is focused in f and g. CD31 immunostaining demonstrates endothelial cells surrounding dilated vascular lumina (g). However, they are not accompanied by perivascular structure, which are demonstrated as lacks of both black (corresponding to elastic fiber) and dark brown lines (corresponding to collagen fiber) in EVG stain (h)