Histologic features of Polyarteritis nodosa
The pathologic lesion defining classic PAN is a focal and segmental transmural necrotizing vasculitis of medium-sized and small arteries. It less commonly affects arterioles, and involvement of large vessels (aorta) and veins does not occur. The lesions occur in all parts of the body, but less so in the splenic arteries and rarely in the pulmonary arteries. The inflammation is characterized by fibrinoid necrosis and pleomorphic cellular infiltration of the vessel wall, predominantly polymorphonuclear leukocytes with variable numbers of lymphocytes and eosinophils. The normal architecture of the vessel wall, including the elastic laminae, is disrupted. The coexistence of different stages of inflammation, scarring, and normal vessel wall is common. Thrombosis or aneurysmal dilation may occur at the site of the lesion.
