Figure 1 (A) Extensive (grade 3) solid microvascular proliferation amid the large vessels of an arteriovenous malformation (H&E). (B) Same area as in fig 3A showing distinct closely packed vascular structures in anti‐1a actin immunostain (SMA‐1). (C) Details taken from boxed area in fig 3A showing solid‐appearing growth of swollen vascular cells with inconspicuous lumina (H&E). (D) Details taken from boxed area showing well‐outlined vascular walls of small vessels in SMA‐1 immunostain. (E) Details taken from boxed area showing the luminal endothelial component of the vascular proliferation in anti‐CD31 immunostain.