Figure 2

(a) Polyarteritis nodosa. Medium-sized artery in the tunica albuginea with segmental transmural necrotizing inflammation of the vessel wall and thrombotic occlusion of the lumen. (b) Artery affected by polyarteritis nodosa at a later stage with partly destroyed wall and occlusion of the lumen by a fibroblastic proliferation and marked surrounding mononuclear inflammatory infiltrate. Note the beginning fibrinoid necrosis, as usually seen in a still later stage. (c) Detail of the fibroblastic proliferation in the lumen of an occluded artery with formation of new capillar lumina surrounded by an inflammatory infiltrate.