Figure 1. Case C.

A & B. Lateral and A-P carotid angiograms. Large left frontal AVM at diagnosis, prior to gamma knife treatment (2002). AVM is fed predominantly by left dysplastic ACA with small flow-related aneurysms. The deep drainage is via enlarged left basal vein of Rosenthal to Vein of Galen. There is a coil-excluded basilar tip aneurysm.

C. Pre-surgical angiogram (2010) shows a markedly decreased but still present nidus, now with superficial-only drainage.

D. Intermediate magnification of Hematoxylin and Eosin stain showing vascular structures and intervening parenchyma in AVM. There are intraluminal foamy macrophages and a mixed lymphoplasmacytic inflammatory infiltrate surrounding the vascular structures containing numerous macrophages and neutrophils. The surrounding neuropil demonstrates reactive gliosis. E. High magnification Hematoxylin and Eosin stain of AVM with markedly thickened vessels and intervening parenchymal and perivascular inflammatory infiltrates that include lymphocytes, neutrophils and macrophages.

F. 10x magnification of paraffin tissue section of resection surgical specimen; stained for CD68. Macrophage infiltration is prominent is vessels walls.

G. 20x magnification. Scattered intraluminal positive cells are seen, but the macrophage density is clearly seen in walls of vascular structures and intervening gliotic tissue.

H. 20x magnification. Similar to G, with more extensive macrophage infiltration into vascular wall.

I. Low magnification H/E stain showing localization of scattered Prussian Blue positive staining

J. High magnification H/E stain showing localization of scattered Prussian Blue positive staining (arrows).