Figure 3.

Longitudinal views of plexiform lesions in PPH. (A) Low-power magnification of a pulmonary artery stained for MSA. Distal to the bifurcation of the muscular artery, the two branching vessels are occluded by plexiform lesions (arrows). The thin smooth muscle layers of the bronchiolar and pulmonary arteries are highlighted by the MSA stain (short arrows). (B) Higher-power magnification of the same lesion stained with FVIII-r.ag. In this example, the endothelial cells lining the multiple lumina of the plexiform lesions stain positive for FVIII-r.ag. Dilatation lesions can be seen within and adjacent to the plexiform lesions (arrows).